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The mbuna cichlids of Lake Malawi: A model for rapid speciation and adaptive radiation
Abstract
Mbuna, the dominant fishes on the rocky shores of Lake Malawi, have become a major ‘model system’ for the study of rapid speciation and adaptive radiation. At least 295 putative species are known, of which more than 200 remain undescribed. There is no good evidence for monophyly in the mbuna, rather mitochondrial DNA phylogenies indicate that they are polyphlyetic with respect to benthic feeding cichlids of the genera Aulonocara, Alticorpus and some species of Lethrinops. Male mbuna hold territories for 18 months or more and breed year-round. All species are maternal mouthbrooders, but females do not guard free-swimming young. Mbuna are polygamous (both sexes). There is sexual dimorphism in size, colour and fin length, and many species show within-population colour polymorphism. Mbuna genera are largely differentiated on the basis of head, jaw and tooth morphology, but congeneric species are generally distinguished by male colour. Many morphologically specialized forms have broad diets and often feed on common easily obtainable resources. While it is likely that dietary and habitat niche partitioning contributes to species coexistence, this has never clearly been demonstrated under experimental conditions. Populations on spatially separated habitat patches are often genetically differentiated, probably because most species are specialized for life on rocky shores, and lack a dispersal phase in their life histories. Males seem to disperse more than females, but are able to home several kilometres back to their territories. Some closely related ecologically equivalent allopatric populations are differentiated in male colour. Those tested have been shown to mate at least partially assortatively. Sexual selection acting on male colour seems the most plausible mechanism for initial species divergence. The same colour forms seem to have arisen several times, suggesting frequent parallel evolution. The main conservation threat to mbuna at present seems to be translocation of species within the lake as a result of the aquarium trade. However, deleterious effects on indigenous populations are not documented. In the long run, sedimentation, pollution, introduction of alien species and the development of targeted food fisheries could be more serious threats.
... 'Rock-dwelling' Mbuna. The mbuna group dominate the rocky shores of Lake Malawi, and are used as a model system for the study of rapid speciation and adaptive radiation 25,173,174 . Similar to the shallow-benthics, there are hundreds of species, many of which are undescribed 169,174 . ...
... The mbuna group dominate the rocky shores of Lake Malawi, and are used as a model system for the study of rapid speciation and adaptive radiation 25,173,174 . Similar to the shallow-benthics, there are hundreds of species, many of which are undescribed 169,174 . We aimed to maximise our coverage of the phenotypic diversity in the group by sampling multiple genera, which are largely differentiated on the basis of head, jaw and tooth morphology 174 . ...
... Similar to the shallow-benthics, there are hundreds of species, many of which are undescribed 169,174 . We aimed to maximise our coverage of the phenotypic diversity in the group by sampling multiple genera, which are largely differentiated on the basis of head, jaw and tooth morphology 174 . Our dataset 41 includes 7 species (15 individuals) of mbuna, covering 7 of the 14 described mbuna genera (Table 1). ...
Here we describe a dataset of freely available, readily processed, whole-body μCT-scans of 56 species (116 specimens) of Lake Malawi cichlid fishes that captures a considerable majority of the morphological variation present in this remarkable adaptive radiation. We contextualise the scanned specimens within a discussion of their respective ecomorphological groupings and suggest possible macroevolutionary studies that could be conducted with these data. In addition, we describe a methodology to efficiently μCT-scan (on average) 23 specimens per hour, limiting scanning time and alleviating the financial cost whilst maintaining high resolution. We demonstrate the utility of this method by reconstructing 3D models of multiple bones from multiple specimens within the dataset. We hope this dataset will enable further morphological study of this fascinating system and permit wider-scale comparisons with other cichlid adaptive radiations.
... Along with the weak evidence of the evolutionary divergence in visual systems by ambient light environments in Lake Malawi cichlids, Allender et al. (2003) reported that 81 % of rock-dwelling cichlid species in the littoral habitats in Lake Malawi (hereafter, mbuna cichlids; Genner & Turner 2005) commonly have blue flank in male nuptial coloration. This blue flank nuptial coloration is shared across all of the morphologically classified morphs across mbuna species -"all-blue", "yellow-chest", "orange-dorsal" -except for the "all-yellow" morph. ...
... Many mbuna cichlids mainly feed on algae and plankton in the shallow depth of water of 5 to 20 m (Genner & Turner 2005;Holzberg 1978;Markert & Arnegard 2007;Ribbink et al. 1983). At these depths, the ambient light spectrum that transmits best is the blue light spectrum (approximately 450 -575 nm ;Deutsch 1997;Dalton et al. 2010;Smith et al. 2011). ...
... More dominant males of some species (i.e., Metriaclima zebra, Metriaclima benetos, Metriaclima barlowi) have reflectance spectra that are highly skewed towards UV A c c e p t e d M a n u s c r i p t wavelengths (< 400 nm, Jordan et al. 2004a), and some males can engage in the plastic expression of UV reflective bands (Jordan et al. 2004a;Pauers et al. 2016). Territorial mbuna males vigorously fight for better territory (Genner & Turner 2005;Markert & Arnegard 2007), and dominant mbuna males display their dominance by changing their nuptial colorationi.e. brightening their body coloration or increasing UV contrast in their coloration (Andries & Nelissen 1990;Jordan et al. 2004a;Mellor et al. 2012). ...
Female cichlid fish living in African great lakes are known to have sensory systems that are adapted to ambient light environments. These sensory system adaptations are hypothesized to have influenced the evolution of the diverse male nuptial coloration. In rock-dwelling Lake Malawi mbuna cichlids, however, the extent to which ambient light environments influence female sensory systems and potentially associated male nuptial coloration remains unknown. Yet, the ubiquitous blue flank coloration and UV reflection of male mbuna cichlids suggests the potential impacts of the blue-shifted ambient light environment on these cichlid’s visual perception and male nuptial coloration in the shallow water depth in Lake Malawi. In the present study, we explored whether and how the sensory bias of females influences intersexual communication in the mbuna cichlid, Metriaclima zebra. A series of choice experiments in various light environments showed that M. zebra females (i) have a preference for the blue-shifted light environment, (ii) prefer to interact with males in blue-shifted light environments, (iii) do not show a preference between dominant and subordinate males in full-spectrum, long-wavelength filtered, and short-wavelength filtered light environments, and (iv) show a ‘reversed’ preference for subordinate males in the UV-filtered light environment. These results suggest that the visual perception of M. zebra females may be biased to the ambient light spectra in their natural habitat by local adaptation and that this sensory bias may influence the evolution of blue and UV reflective patterns in male nuptial coloration.
... Many sympatric species and allopatric populations of haplochromine cichlid fish differ strikingly in male colour (Allender et al., 2003) and this is particularly true for the rock-dwelling 'mbuna' cichlids of Lake Malawi (Konings, 2007). Closely related sympatric mbuna species may occupy very similar trophic niches, differ slightly in morphology (Genner & Turner, 2005), show extremely conserved behaviour (Myers, 1960) and differ in colour traits associated with secondary sexual characteristics (Konings, 2007). Furthermore, geographical variants of fish considered the same species may differ slightly in traits such as dorsal fin or throat colour (e.g. ...
... Male mbuna cichlids compete aggressively for territories and those males that are unable to secure a territory are unlikely to breed successfully (Genner & Turner, 2005). Territorial males are generally more aggressive to conspecific intruders, with which they compete for mates as well as other resources such as food and shelter (Genner et al., 1999). ...
... Reduced interspecific aggression need not only apply to males; females too can be territorial ( Genner & Turner, 2005;Dijkstra et al., 2008). Signal traits that are thought to influence aggressive responses may be divergent in females as well as males. ...
The rocky shore habitats of the African Great Lakes support high densities of cichlid fishes, including many closely-related/ecologically similar species. Aggressive behaviours between conspecifics, and perhaps heterospecifics, influences this unusually high level of species coexistence. In dichotomous choice aggression trials, male Maylandia thapsinogen were presented simultaneously with two heterospecific intruders (Maylandia emmiltos and Maylandia zebra). M. thapsinogen were significantly more aggressive towards intruders from an allopatric species (similar orange dorsal fin colour - M. emmiltos), than towards a different allopatric species (blue dorsal fin - M. zebra). Aggression biases disappeared when colour differences were masked using monochromatic lighting. A second experiment compared female aggression biases between M. emmiltos with M. thapsinogen, species similarly coloured to one another, the former possessing a yellow, as opposed to a black throat as the latter does. M. thapsinogen preferentially attacked females of their own species in full but not monochromatic light, while female M. emmiltos showed no significant bias in aggression under any lighting. Responses were not affected by olfactory cues provided by the stimulus fish. These results indicate that divergence in colour might facilitate species co-existence in some cases, but not all, which could be important should populations re-join through lake level drops.
... While Jordan et al. (2010) found a possible influence of territory location on mating outcomes, little work has been conducted looking at aspects of territory quality in the mbuna. It is known that these fishes hold territories in leklike (Moyer & Yogo, 1982;Donaldson, 1990) spawning systems, as unlike true leks, mbuna leks contain resources (Genner & Turner, 2005). True leks, as defined by Bradbury (1981), are spawning grounds where males gather and females come to observe and choose mates, and contain no resources. ...
... This finding paired with the findings above warrant further consideration into the role of territory quality. Given that mbuna leks tend to also hold food resources (Genner & Turner, 2005), might variation in food resources also play a role in female choice? We decided to test whether the presence of food resources in two different sized territories affected female choice and male behaviour using Metriaclima zebra (Stauffer et al., 1997; a ubiquitous mbuna in Lake Malawi). ...
... These results show that certain aspects of territory quality can affect female choice of potential mates. Since mbuna are considered to be a model system for adaptive radiation and speciation (Genner & Turner, 2005) and a prime example of a recent divergence (Kornfeld & Smith, 2000), these results could have implications on how certain lineages of cichlid fishes have evolved. It is likely that aspects of territory quality may facilitate the sympatric speciation of cichlids in addition to the usuallyattributed forces of intersexual and intrasexual selection. ...
The cichlid fishes of Lake Malawi are an excellent model group with which to study adaptive radiation and speciation; due to the vast number of individual species, large variation in feeding adaptations and behaviours, and relatively recent divergence are found. Males of many cichlid species will obtain and defend lek-like territories, where they court potential mates in addition to foraging for food. Aspects of territory quality warrant investigation because of the relationship between reproductive success and territory defence success. In this study, we tested whether the presence of a small or large food resource had any effect on the preference of a gravid female for a potential mate. The results of this experiment suggest that the presence of a large food resource increases the attractiveness of a male to a potential mate. This may suggest that the presence of food alone may not be the most important factor, or there may be a threshold amount over which females are attracted. These results indicate that certain aspects of territory quality such as habitat type or proximity to a food resource may play a role in both intersexual and intrasexual selection mechanisms: perhaps even driving and possibly accelerating the speciation of certain lineages of cichlid fishes.
... Likewise, if speciation is initially characterised by segregation into trophic niches, we may expect an accompanying disparity in lateral line morphology [24]. In Lake Malawi cichlids, trophic resources range from highly motile fish, to cryptic infaunal invertebrates, and sessile algae [25][26][27], and each food is associated with specific lateral line structures in the species that consume them [15,19,28]. This indicates that lateral line system diversity is likely to play a role in the radiation of the cichlids of Lake Malawi. ...
... The typically open-water feeding Rhamphochromis and Diplotaxodon clades, and the demersal feeding "shallow benthic" and "deep benthic" clades, had on average the greatest number of neuromasts in their trunk canals ( Fig. 5f-i). Conversely, mbuna species inhabiting the rocky-shore littoral zone of Lake Malawi, that predominantly feed on epilithic algae and allied resources [26,45] generally have few trunk canal and superficial neuromasts ( Fig. 5f-i). Notably, A. calliptera had a similar number of neuromasts to the mbuna species. ...
Background
The mechanosensory lateral line system is an important sensory modality in fishes, informing multiple behaviours related to survival including finding food and navigating in dark environments. Given its ecological importance, we may expect lateral line morphology to be under disruptive selection early in the ecological speciation process. Here we quantify the lateral line system morphology of two ecomorphs of the cichlid fish Astatotilapia calliptera in crater Lake Masoko that have diverged from common ancestry within the past 1,000 years.
Results
Based on geometric morphometric analyses of CT scans, we show that the zooplanktivorous benthic ecomorph that dominates the deeper waters of the lake has large cranial lateral line canal pores, relative to those of the nearshore invertebrate-feeding littoral ecomorph found in the shallower waters. In contrast, fluorescence imaging revealed no evidence for divergence between ecomorphs in the number of either superficial or canal neuromasts. We illustrate the magnitude of the variation we observe in Lake Masoko A. calliptera in the context of the neighbouring Lake Malawi mega-radiation that comprises over 700 species.
Conclusions
These results provide the first evidence of divergence in this often-overlooked sensory modality in the early stages of ecological speciation, suggesting that it may have a role in the broader adaptive radiation process.
... Given the recurrent evolution of hypertrophied lips across these major East African cichlid lineages, it is plausible that the phenotype has also evolved independently multiple times in Lake Malawi (Hulsey et al. 2018). With roughly 850 species of haplochromine cichlids inhabiting this large African lake ( fig. 2), the opportunity for adaptive traits to arise repeatedly in Malawi is considerable (Danley and Kocher 2001;Genner and Turner 2005;Konings 2007). The vast majority of Lake Malawi endemic cichlids belong to the tribe Haplochromini, but in this lake, have traditionally been placed in two main lineages: the primarily rock-dwelling mbuna (Genner and Turner 2005) and the largely sand-dwelling nonmbuna (Danley and Kocher 2001). ...
... With roughly 850 species of haplochromine cichlids inhabiting this large African lake ( fig. 2), the opportunity for adaptive traits to arise repeatedly in Malawi is considerable (Danley and Kocher 2001;Genner and Turner 2005;Konings 2007). The vast majority of Lake Malawi endemic cichlids belong to the tribe Haplochromini, but in this lake, have traditionally been placed in two main lineages: the primarily rock-dwelling mbuna (Genner and Turner 2005) and the largely sand-dwelling nonmbuna (Danley and Kocher 2001). These major ecomorphological groups have also consistently been recovered as distinct clades in molecular phylogenetic analyses (Meyer et al. 1990(Meyer et al. , 1996Meyer 1993;Hulsey et al. 2017Hulsey et al. , 2018Malinsky et al. 2018). ...
Cichlid fishes have repeatedly evolved an astounding diversity of trophic morphologies. For example, hypertrophied lips have evolved multiple times in both African and Neotropical cichlids and could have even evolved convergently within single species assemblages such as African Lake Malawi cichlids. However, the extremely high diversification rate in Lake Malawi cichlids and extensive potential for hybridization has cast doubt on whether even genome-level phylogenetic reconstructions could delineate if these types of adaptations have evolved once or multiple times. To examine the evolution of this iconic trait using protein-coding and non-coding single nucleotide polymorphisms (SNPs), we analyzed the genomes of 86 Lake Malawi cichlid species, including 33 de novo resequenced genomes. Surprisingly, genome-wide protein-coding SNPs exhibited enough phylogenetic informativeness to reconstruct inter- and intra-specific relationships of hypertrophied lip cichlids, although non-coding SNPs provided better support. However, thinning of non-coding SNPs indicated most discrepancies come from the relative smaller number of protein-coding sites and not from fundamental differences in their phylogenetic informativeness. Both coding and non-coding reconstructions showed that several “sand-dwelling” hypertrophied lip species, sampled intraspecifically, form a clade interspersed with a few other non-hypertrophied lip lineages. We also recovered Abactochromis labrosus within the rock-dwelling “mbuna” lineage, starkly contrasting with the affinities of other hypertrophied lip taxa found in the largely sand-dwelling “non-mbuna” component of this radiation. Comparative analyses coupled with tests for introgression indicate there is not widespread introgression between the hypertrophied lip lineages and taken together suggest this trophic phenotype has likely evolved at least twice independently within Lake Malawi.
... The lakes of Africa harbor the richest diversity of cichlid species, where massive species radiation happened during the last 10 million years. Cichlids exhibit interesting patterns of adaptive radiation and speciation which make them excellent models for studying evolutionary diversification and speciation (Kocher, 2004;Genner and Turner, 2005;Seehausen, 2006;Takeda et al., 2013;Brawand et al., 2014). Cichlids in India comprise species belonging to the genus Etroplus, mainly E. suratensis, E. canarensis and E. maculatus. ...
... The unique diversity in ecology, morphology, and behavior makes Cichlids good model systems for evolutionary biology, evolutionary genetics and phenotype-genotype relationship studies (Barlow, 2000). Allopatric and sympatric speciation have been suggested as mechanisms driving rapid speciation and adaptive radiation of Cichlids in different lakes (Kocher, 2004;Genner and Turner, 2005). Recent molecular genetic studies in many Cichlid species provided evidence for substructuring and speciation due to environmental discontinuities over smaller geographical scales (Seehausen, 2006;Takeda et al., 2013;Brawand et al. 2014). ...
Etroplus suratensis is one of the most important indigenous Cichlids of the Indian subcontinent exhibiting restricted distribution in the estuaries of peninsular India and Sri Lanka. Coastal pollution and climate change contribute to the deterioration of their habitats. Etroplus suratensis is widely distributed along estuaries and brackishwater lakes of India which make them ideal candidates for investigations on adaptation and selection on mitochondrial Oxidative Phosphorylation (OXPHOS) genes. We investigated the selection patterns in the OXPHOS system of E. suratensis by comparing OXPHOS genes of 105 fishes collected from different eco-regions in India. Signals of positive and diversifying selection observed in the mitogenomes were correlated with habitat characteristics. Habitat specific mutational signals observed have adaptive significance as the populations of the study represented humid tropical climatic zones constituting rainforests in the southwest, semi-arid zones in the southeast and humid subtropical zones in the northeast regions of India. Adaptation to these environmentally heterogeneous habitats generates genotypic and phenotypic variants with specific metabolic or bioenergetic requirements. The observed adaptive mitogenome evolution may be the imprints of this geographic variability, genetic drift and selective forces imparted by the distinctive ecoregions which form their habitats.
... In Tanganyikan cichlids, another 566 trophic trait, gill raker length, is sexually dimorphic in uniparental mouthbrooders but not 567 biparental mouthbrooders, providing strong support that sexual dimorphism in reproductive 568 strategies can lead to sexual dimorphism in trophic traits (Ronco et al., 2019). Body size is also 569 sexually dimorphic to varying degrees among Lake Malawi cichlids, with males generally being 570 larger in size (Genner and Turner, 2005). Given the interactive relationship between body size 571 and gut length, sex-specific genetic architectures may have co-evolved to counter maladaptive 572 outcomes in gut length for one or both sexes arising from evolution of sexual dimorphism in 573 body size. ...
Variation in gastrointestinal morphology is associated with dietary specialization across the animal kingdom. Gut length generally correlates with trophic level, and increased gut length in herbivores is a classic example of adaptation to cope with diets with lower nutrient content and a higher proportion of refractory material. However, the genetic basis of gut length variation remains largely unstudied, partly due to the inaccessibility and plasticity of the gut tissue, as well as the lack of dietary diversity within traditional model organisms relative to that observed among species belonging to different trophic levels. Here, we confirm the genetic basis of gut length variation among recently evolved Lake Malawi cichlid fish species with different dietary adaptations. We then produce interspecific, inter-trophic-level hybrids to map evolved differences in intestinal length in an F2 mapping cross between Metriaclima mbenjii, an omnivore with a relatively long gut, and Aulonocara koningsi, a carnivore with a relatively short gut. We identify numerous candidate quantitative trait loci for evolved differences in intestinal length. These quantitative trait loci are predominantly sex-specific, supporting an evolutionary history of sexual conflicts for the gut. We also identify epistatic interactions potentially associated with canalization and the maintenance of cryptic variation in the cichlid adaptive radiation. Overall, our results suggest a complex, polygenic evolution of gut length variation associated with trophic level differences among cichlids, as well as conflicts and interactions that may be involved in evolutionary processes underlying other traits in cichlids.
... Cichlids are one of the most species-rich families of teleosts and have an outstanding diversity of pigment patterns that play a key role in ecological and evolutionary processes. Pigment pattern is one of the most important morphological traits that strongly affected the adaptation and exceptional rate of speciation, such as diversification along signal traits in the adaptive radiation of African cichlids (Genner & Turner, 2005;Salzburger, 2009;Miyagi & Terai, 2013;. ...
Cichlids exhibit an outstanding diversity of pigment patterns among both teleosts and vertebrates in general. The role of endocrine regulatory mechanisms underlying the observed diversity of patterns remains poorly understood. Thyroid hormones are important signaling molecules that regulate a wide range of developmental processes in teleosts. Here, I review evidence for the influence of thyroid signaling on pigment pattern formation in Neotropical cichlids, and the role of hormone-mediated phenotypic plasticity and heterochrony in the evolution of cichlid pattern. The use of hormones as key factors in switching developmental programs in future studies will provide a better understanding of how environmentally-mediated changes in the endocrine regulation of ontogeny contribute to adaptive evolution and the phenotypic divergence of cichlids.
... However, regional isolation has been well known to play an important role in the evolution and preservation of phenotypic variation in cichlids in rivers and lakes (Piálek et al., 2012;Seehausen and Magalhaes, 2010). Structured littoral fish species in lakes have more significant color variation than pelagic or deep-water demersal species (Genner and Turner, 2005;Koblmüller et al., 2008). Studies on cichlid populations in African lakes confirmed that populations of stenotopic species, i.e., species with narrow specialization under certain environmental conditions, are often isolated from each other, even by small habitat barriers (Koblmüller et al., 2011;Sefc et al., 2007;Smith and Kornfield, 2002). ...
Cichlid fishes exhibit rapid adaptive radiations with significant diversification rates in response to ecological variability, i.e., ecological opportunity or geographical isolation. The discovery of a Midas cichlid species in Lake Batur, Indonesia’s largest volcanic lake, first reported in 2013, could represent such adaptations. Midas cichlids can now be found in a range of habitats in Lake Batur and dominate the lake’s fish population by up to 60%. This study aimed to identify the interaction between habitat, water quality, and Midas cichlid in Lake Batur, facilitating morphometric variances in the fish populations. The fish were captured at five locations in Lake Batur using fishing
rods, community nets with mesh sizes of 2–3 inches, experimental gillnets with mesh sizes of 1 inch, and fish scoops in floating net cages during August and November 2022. There were 46 fish samples caught from the five stations, all photographed using a digital camera and later measured using the ZEN 2012 software. The fish measurement employed a truss morphometric method using 21 distinct morphometric body features. Canonical analysis was used to determine the distribution of characteristics, while discriminant analysis was used to examine the closeness of association. The measured water quality parameters included pH, DO, temperature, conductivity, and TDS for in-situ and TSS, TP, TN, and chlorophyll A for ex-situ. The findings revealed morphometric changes among Midas cichlid species in Lake Batur caused by habitat and water quality differences. The distinction can be detected in the
anterior and posterior bodies (C1, B1, C3, C6, C5, B3 and B4). Temperature and aquatic plants, Azolla pinnata, may detect the station and shape of fish in Lake Batur. Body shape cannot be identified by chlorophyll A, TN, DO, and TDS. Future genetic research could answer why fish groups with varied body types coexist in the same location.
... The cichlid fishes are a quintessential example of rapid "explosive" adaptive radiation and phenotypic diversification (Genner & Turner, 2005;Henning & Meyer, 2014;Kocher, 2004;Meyer, 1993;Meyer et al., 1990;Salzburger, 2018). Among cichlid radiations, the most species-rich are the multiple radiations in the Great Lakes of East Africa-Victoria, Malawi, and Tanganyika -where hundreds of species evolved in a remarkably short time span (Kocher, 2004). ...
The cichlid fishes comprise the largest extant vertebrate family and are the quintessential example of rapid "explosive" adaptive radiations and phenotypic diversification. Despite low genetic divergence, East African cichlids harbor a spectacular intra- and interspecific morphological diversity, including the hyper-variable, neural crest (NC)-derived traits such as coloration and craniofacial skeleton. Although the genetic and developmental basis of these phenotypes has been investigated, understanding of when, and specifically how early, in ontogeny species-specific differences emerge, remains limited. Since adult traits often originate during embryonic development, the processes of embryogenesis could serve as a potential source of species-specific variation. Consequently, we designed a staging system by which we compare the features of embryogenesis between three Malawi cichlid species-Astatotilapia calliptera, Tropheops sp. 'mauve' and Rhamphochromis sp. "chilingali"-representing a wide spectrum of variation in pigmentation and craniofacial morphologies. Our results showed fundamental differences in multiple aspects of embryogenesis that could underlie interspecific divergence in adult adaptive traits. First, we identified variation in the somite number and signatures of temporal variation, or heterochrony, in the rates of somite formation. The heterochrony was also evident within and between species throughout ontogeny, up to the juvenile stages. Finally, the identified interspecific differences in the development of pigmentation and craniofacial cartilages, present at the earliest stages of their overt formation, provide compelling evidence that the species-specific trajectories begin divergence during early embryogenesis, potentially during somitogenesis and NC development. Altogether, our results expand our understanding of fundamental cichlid biology and provide new insights into the developmental origins of vertebrate morphological diversity.
... Froese, 1997;Strona, 2014;Thorson et al., 2014). Additional information from 41 further sources was also included (Fricke, 1980(Fricke, , 1986Lobel and Johannes, 1980;Thresher, 1980Thresher, , 1984Wallace and Selman, 1981;Hourigan and Kelley, 1985;Colin and Clavijo, 1988;Brichard, 1989;Colin, 1989;Tricas, 1989;Barlow, 1991;Colin and Bell, 1991;Fowler, 1991;Roberts and Ormond, 1992;Axelrod, 1993;Kuwamura, 1997;Nagoshi and Yanasigawa, 1997;DeMartini, 1998;Gibson, 1998;Righton et al., 1998;Coward and Bromage, 2000;Mylonas and Zohar, 2000;Avise et al., 2002;Zekeria et al., 2002;Murua and Saborido-Rey, 2003;Gibran et al., 2004;Heg et al., 2004;Whiteman and Côté, 2004;Ah-King et al., 2005;Genner and Turner, 2005;Gonzalez-Voyer et al., 2008;Fitzpatrick et al., 2009;Collette, 2010;Takemura et al., 2010;Sogabe and Ahnesjö, 2011;Bellwood and Pratchett, 2013;Pyron et al., 2013;Hughes et al., 2014;Mcbride et al., 2015;Dey et al., 2017). ...
Although several hypotheses have been proposed to explain the emergence of social monogamy, its origin is still intensely debated. Monogamy has many potential drivers, but evolutionary causality among them remains unclear. Using phylogenetic comparative methods within a Bayesian framework we explored the evolution of monogamy in cichlids and in marine reef fishes because, while both groups are characterised by unusually high incidence of social monogamy, they face very different ecological challenges. For each group, we examined four classic hypotheses that explain the evolution of monogamy: female dispersal, male mate guarding, female–female intolerance, and the biparental care hypotheses. We also explored whether the ecological traits of diet and shelter use are evolutionarily coupled with these hypotheses or with monogamy. First, we found that the evolution of monogamy was predicted by male territoriality in cichlids and simultaneous male and female territoriality in marine reef fishes. We suggest that these results provide support for the male mate guarding hypothesis in cichlids and female–female intolerance hypothesis in marine reef fishes. Second, we demonstrate clear evidence against the biparental care hypothesis, as biparental care was a consequence, not a cause, of monogamy in our analyses. Third, as female dispersal drove the loss of monogamy in both cichlids and marine reef fishes, this suggests the female dispersal hypothesis is not driving the evolution of monogamy in either group. These findings in two highly-monogamous fish taxa largely support prior findings from primate and bird comparative studies and provide novel large-scale evidence for a link between mate guarding and the evolution of monogamy.
... Many species of African cichlids are characterized by sexual dichromatism, when males have a bright and well-defined pigment pattern, while females have a duller and less distinctive pattern (Genner and Turner 2005;Brzozowski et al. 2012;Parichy and Liang 2021). Among Neotropical cichlids, there are species with reversed sexual dichromatism (Tobler 2007;Říčan et al. 2016). ...
Neotropical cichlids are a group of fish among which there are species with reversed sexual dichromatism, where females have carotenoid-based coloration that males lack. Carotenoid coloration can vary depending on the environment and the distribution of other types of chromatophores in the pigment pattern. The role of thyroid hormones (THs), one of the main signaling molecules regulating fish ontogeny, in the diversity of carotenoid coloration in Neotropical cichlid females remained poorly understood. In this work, using the species Amatitlania nigrofasciata, the effect of elevated TH level on the development of reversed sexual dichromatism was shown. Increases in TH signaling in experimental fish led to heterochrony in the development of the pigment pattern and phenotypic variability with the appearance of variants of carotenoid pigmentation similar to other Neotropical cichlid species. The extent of carotenoid-based ventral coloration of females depended on TH-induced changes in the melanistic pattern. The results obtained testify in favor of the important role of the TH signaling pathway in the diversification of the carotenoid coloration of Neotropical cichlids and provide new perspectives for studying the role of plasticity in the evolutionary adaptation of cichlid fishes.
... Cichlid fishes are evolutionary model organisms for studying the process of speciation, mostly due to their exceptionally high diversity and ultra-fast rates of phenotypic divergence (Meyer et al. 1990, Kocher 2004, Genner and Turner 2005. Cichlids famously vary in morphological traits, such as body coloration and their trophic morphology, but also in behavioral traits, such as social systems and parental care (Meyer 1993, Seehausen 1997, Stiassny and Meyer 1999, Wisenden et al. 2015. ...
... The heterochrony was also evident within and between species throughout 34 ontogeny, up to the juvenile stages. Finally, the identified interspecific differences in the The cichlid fishes are a quintessential example of rapid "explosive" adaptive radiation and 45 phenotypic diversification (Genner and Turner, 2005; Henning and Meyer, 2014; Kocher,46 2004; Meyer, 1993;Meyer et al., 1990;Salzburger, 2018). Among cichlid radiations, the 47 most species-rich are the multiple radiations in the Great Lakes of East Africa -Victoria, 48 Malawi, and Tanganyika -where hundreds of species evolved in a remarkably short time 49 span (Kocher, 2004). ...
The cichlid fishes comprise the largest extant vertebrate family and are the quintessential example of rapid “explosive” adaptive radiations and phenotypic diversification. Despite low genetic divergence, East African cichlids harbour a spectacular intra- and interspecific morphological diversity, including the hyper-variable, neural crest (NC)-derived traits such as colouration and craniofacial skeleton. Although the genetic and developmental basis of these phenotypes has been investigated, understanding of when, and specifically how early, in ontogeny species-specific differences emerge, remains limited. Since adult traits often originate during embryonic development, the processes of embryogenesis could serve as a potential source of species-specific variation. Consequently, we compared the features of embryogenesis between three Malawi cichlid species – Astatotilapia calliptera, Tropheops sp. ‘mauve’ and Rhamphochromis sp. ‘chilingali’ – representing a wide spectrum of variation in pigmentation and craniofacial morphologies. Our results showed fundamental differences in multiple aspects of embryogenesis that could underlie interspecific divergence in adult adaptive traits. Firstly, we identified variation in the somite number and signatures of temporal variation, or heterochrony, in the rates of somite formation. The heterochrony was also evident within and between species throughout ontogeny, up to the juvenile stages. Finally, the identified interspecific differences in the development of pigmentation and craniofacial cartilages, present at the earliest stages of their overt formation, provide compelling evidence that the species-specific trajectories begin divergence during early embryogenesis, potentially during somitogenesis and NC development. Altogether, our results expand our understanding of fundamental cichlid biology and provide new insights into the developmental origins of vertebrate morphological diversity.
Research highlights
This work details the early development of three divergent Lake Malawi cichlids. A comparative analysis reveals anatomical and timing differences during embryogenesis and indicates divergence of species’ morphologies prior to their overt formation.
... We show that power is unequally distributed in each dominance hierarchy, with a relatively small subset of territorial males affirming their social dominance by chasing nondominant fish and showing symmetrical aggressive displays to each other to establish territorial boundaries. These findings are consistent with the pronounced territoriality typically seen in many haplochromines and other cichlid species (Maan et al., 2004;Genner & Turner, 2005;Salzburger, 2009). We found rapid changes in behavior after social rank transitions; however, to our surprise males that attained social dominance already exhibited dominant-like behaviors prior to social ascent (i.e., territory acquisition). ...
Within social dominance hierarchies, rank has a major impact on health and fitness. Dominance hierarchies are rarely stable as individuals may change rank due to changes in the social environment. Here we describe general group-level social network properties and changes in social ties and behavior during rank transitions in 16 communities of the cichlid Astatotilapia burtoni. Social networks based on chases were dense with dominant males frequently chasing subordinate males and females. This intense territoriality of dominant males was also reflected by a high degree of ‘power’ inequality. Compared to chase-based networks, display-based networks were characterized by a high degree of reciprocity due to display behaviors mostly occurring bidirectionally among a few highly ranked males. Territory ownership is tightly linked to social dominance and territory loss (i.e., social descent) was, as expected, associated with a sharp reduction in aggression level and an increase in chases received. However, although territory acquisition (i.e., social ascent) was an abrupt process, ascending males displayed elevated aggression prior to ascent, in sharp contrast to previous studies carried out in less complex settings. Together, our results provide novel insights into dynamic changes in behavior in cichlid dominance hierarchies.
... For instance, terminal mouths protrude in the same direction as the fish's body thereby enhancing the ability to rapidly close the distance to a prey item in open water (Waltzek & Wainwright, 2003). Conversely, benthicfeeding species that feed from algae-covered rocks or by excavating sandy substrates often have subterminal mouths (Motta, 1984;Genner & Turner 2005). Transitions between feeding benthically or feeding in the water column represent major trophic shifts that have occurred repeatedly in Lake Malawi cichlids (Hulsey et al., 2013). ...
Variation in jaw protrusion is critical to cichlid fish trophic diversification. For instance, jaw protrusion distance can influence suction, attack speed, as well as bite force, and jaw protrusion angle is associated with exploiting prey from different substrates. Interestingly, premaxillary ascending process length has been shown to influence the maximum distance some cichlid fishes protrude their oral jaws, but its relationship to jaw protrusion angle is unclear. Using phylogenetic comparative methods, morphometrics, and field measurements in Malawi cichlid species, we tested the relationship between the length of the premaxillary ascending process and two components of jaw protrusion. In Malawi, the premaxilla's ascending process length ranged from 6.9 to 15.2% with respect to standard length. Maximum jaw protrusion ranged from 1.4 to 9.1% of standard length and jaw protrusion angle varied from 17° to 76°. Although jaw protrusion angle was not associated with premaxillary ascending process length, phylogenetically adjusted correlations between the ascending process and maximum jaw protrusion distance were highly significant. Evolutionary change in the premaxilla is likely critical for determining the maximum distance, but not the angle, of Malawi cichlid jaw protrusion. Examinations of this type of potential phenotypic multi-functionality will continue to illuminate the mechanisms contributing to cichlid fish diversity.
... Specifically, K. eisentrauti consumes the most plant tissue, P. maclareni is the only species that consumes sponge tissue, S. mariae is the only species to consume ants, S. mongo's diet is primarily shrimp, and S. pindu is the only species to consume Trichopteran larvae (Figures 1 and 2). Herbivory is common among African cichlids (Genner & Turner, 2005;Ribbink & Lewis, 1982), and K. eisentrauti was previously qualitatively described as a plant specialist (Trewavas et al., 1972). ...
Trophic niche partitioning is observed in many adaptive radiations and is hypothesised to be a central process underlying species divergence. However, patterns of dietary niche partitioning are inconsistent across radiations and there are few studies of niche partitioning in putative examples of sympatric speciation. Here, we conducted the first quantitative study of dietary niche partitioning using stomach contents and stable isotope analyses in one of the most celebrated examples of sympatric speciation: the cichlid radiation from crater lake Barombi Mbo, Cameroon. We found little evidence for trophic niche partitioning among cichlids, including the nine species coexisting in the narrow littoral zone. Stable isotope analyses supported these conclusions of substantial dietary overlap. Our data, however, did reveal that five of 11 species consume rare dietary items, including freshwater sponge, terrestrial ants, and nocturnal foraging on shrimp. Stomach contents of the spongivore (Pungu maclareni) were 20% freshwater sponge, notable considering that only 0.04% of all fishes consume sponges. Overall, we conclude that cichlid species in lake Barombi Mbo overlap considerably in broad dietary niches – in part due to the large proportion of detritus in the stomach contents of all species – but there is evidence for divergence among species in their diet specializations on unique resources. We speculate that these species may utilise these additional specialised resources during periods of low resource abundance in support of Liem's paradox.
... In less than one million years, approximately 800-1200 species of cichlids have evolved within the lake basin, which is an astoundingly fast rate of evolution (Ivory et al., 2016). These fishes have become extremely important models for evolutionary and ecological research, especially for understanding the role behavior plays in driving the evolution of biological diversity (Genner & Turner, 2005;Kornfield & Smith, 2000;Salzburger et al., 2014). In particular, the rock-dwelling haplochromine cichlids known collectively as the "mbuna" have been very popular study subjects for these behavioral studies, largely due to the bright, species-specific, colors of the males, and their robust behaviors in captivity (Couldridge & Alexander, 2001;Jordan et al., 2003;McElroy & Kornfield, 1990). ...
In sexually reproducing taxa, reproductive isolation is key to speciation. Given the speed with which behavioral reproductive isolation evolves, this form of isolation is of particular importance to rapidly evolving species. Here we examine behavioral reproductive isolation in a sympatric, congeneric pair of rock‐dwelling cichlids from Lake Malaŵi, testing the hypothesis that females should prefer conspecific males. We used a pair of Labeotropheus, L. fuelleborni Ahl and L. trewavasae Fryer, from the Chidunga Rocks in southwestern Lake Malaŵi, to test this hypothesis, with the prediction that females would approach conspecific males more frequently than they would heterospecific males. When given a choice between a male L. fuelleborni and L. trewavasae, we found that females did approach males of their own species more frequently than males of the opposite species, and that differences in length and the number of eggspots on the anal fin between the stimulus males had no effect on a female's choice. These results are consistent with behavioral reproductive isolation between these sympatric species, and add further support to the hypothesis that sexual selection played a key role in the speciation of cichlid fishes from Lake Malaŵi. Sympatric Labeotropheus display assortative mating with strong female preference for conspecific males. LEFT PANEL: (A) Female Labeotropheus fuelleborni (spotted fish) prefer conspecific males (dark blue with red dorsal fin), and (B) female L. trewavasae (grey fish) prefer L. trewavasae males (light blue). (C) Males may court heterospecific females but are typically ignored by these females. RIGHT PANEL: Females respond strongly and preferentially to conspecific males.
... The African Great lakes of Tanganyika, Malawi (Nyasa/Niassa) and Victoria provide essential and high-quality food for millions of people, livelihoods for tens of thousands and a range of other ecosystem services. Adaptive radiation of fish of the Cichlidae family and other fauna has led to exceptional biodiversity (Coulter, 1991 ;Genner and Turner, 2005;Lowe-McConnell, 2009;Sturmbauer, 1998), making the lakes a unique global heritage as well as classic biodiversity "hot spots", subject to both high human impact and conservation importance (Darwall et al., 2011). ...
... Similar changes in different lineages could have increased the probability of parallelisms, leading to the homoplastic pattern of character changes. This has also been observed in sexually dimorphic cichlid fish and sticklebacks, in which body size and colour also evolved in parallel across divergent lineages, implicating sexual selection as one of their major engines of speciation (Boughman et al., 2005;Genner & Turner, 2005). ...
Sexual selection has been shown to drive speciation. In dwarf spiders (erigonines), males possess diverse, sexually selected prosomal structures with nuptial-gift-producing glands. The genus Oedothorax is suitable for investigating the evolution of these features due to high structural variation. We have re-delimited this genus based on a phylogenetic analysis. Ten species are Oedothorax s.s.; five are transferred back to their original generic placement; 25 remain unplaced as ‘Oedothorax’. Four junior synonymies are proposed: Callitrichia simplex to Ca. holmi comb. nov.; Gongylidioides kougianensis to G. insulanus comb. nov.; Ummeliata ziaowutai to U. esyunini comb. nov.; Oe. kathmandu to Mitrager unicolor comb. nov. Oedothorax seminolus is a junior synonym of Soulgas corticarius and the transfer of Oe. alascensis to Halorates is confirmed. The replacement name Ca. hirsuta is proposed for Ca. pilosa. The male of Callitrichia longiducta comb. nov. and the female of ‘Oedothorax’ nazareti are newly described. Thirty-eight Oedothorax species are transferred to other genera. Callitrichia spinosa is transferred to Holmelgonia. Three genera are erected: Cornitibia, Emertongone and Jilinus. Ophrynia and Toschia are synonymized with Callitrichia. Character optimization suggests multiple origins of different prosomal modification types. Convergent evolution in these traits suggests that sexual selection has played an important role in erigonine diversification.
... The adaptive radiations of cichlid fishes offer a great opportunity to investigate the contribution of standing genetic variation to rapid adaptive divergence, due to their exceptionally high diversity in species and the repeated evolution of multiple phenotypes (Meyer, et al. 1990;Meyer 1993;Stiassny and Meyer 1999;Kocher 2004;Genner and Turner 2005;. Within the Great Lakes of the African Rift Valley, cichlids diversified into hundreds of endemic species in several lakes of different sizes and ages. ...
The adaptive radiations of East African cichlid fish in the Great Lakes Victoria, Malawi, and Tanganyika are well known for their diversity and repeatedly evolved phenotypes. Convergent evolution of melanic horizontal stripes has been linked to a single locus harboring the gene agouti-related peptide 2 (agrp2). However, where and when the causal variants underlying this trait evolved and how they drove phenotypic divergence remained unknown. To test the alternative hypotheses of standing genetic variation versus de novo mutations (independently originating in each radiation), we searched for shared signals of genomic divergence at the agrp2 locus. While we discovered similar signatures of differentiation at the locus level, the haplotypes associated with stripe patterns are surprisingly different. In Lake Malawi, the highest associated alleles are located within and close to the 5' untranslated region of agrp2 and likely evolved through recent de novo mutations. In the younger Lake Victoria radiation, stripes are associated with two intronic regions overlapping with a previously reported cis-regulatory interval. The origin of these segregating haplotypes predates the Lake Victoria radiation since they are also found in more basal riverine and Lake Kivu species. This suggest that both segregating haplotypes were present as standing genetic variation at the onset of the Lake Victoria adaptive radiation with their more than 500 species and drove phenotypic divergence within the species flock. In summary, both new (Lake Malawi) or ancient (Lake Victoria) allelic variation at the same locus can fuel rapid and convergent phenotypic evolution.
... Both species belong to the Pseudotropheus zebra species complex, which consists of morphological and behaviourally similar species (Stauffer Jr. et al., 1997;Stauffer Jr. & Hert, 1992). They are polygamous, the males are larger than females, with larger pelvic and dorsal fins, and males exhibit brighter colours (Genner & Turner, 2005). M. callainos occurs in Nkatha Bay, Likoma, Namalenje and Thumbi West Island (Kasembe, 2017), while M. estherae is found in Minos Reef, Chilucha Reef, Metangula, Nkhungu and Masinje (Kasembe, 2017). ...
Cichlids are one of the most diverse and colourful groups of freshwater fishes in the world. Despite much investigation, the factors that promote speciation in these fishes are still uncertain. However, previous studies suggest that sexual selection on male colour is one of the main drivers of speciation among these fishes. Metriaclima estherae is a polymorphic cichlid species from Lake Malawi, and thus provides an ideal model for the investigation of the importance of colour as a species recognition cue. M. callainos is a closely related and morphologically similar species, with male colour pattern very similar to that of M. estherae. We tested female choice by giving females of the two species a choice between conspecific and heterospecific males in the presence and absence of visual (colour) and chemical cues. The results show that females of M. callainos were able to reliably recognize conspecific males, even when colour was eliminated as a cue. However, females of M. estherae did not prefer conspecific males, although they were able to discriminate between red and blue conspecific colour morphs by using chemical cues. These results suggest that species recognition cues may differ even among closely related species of cichlid fish, and that female preferences for male coloration may be weak in certain species.
... Cichlid fishes are evolutionary model organisms for studying the process of speciation, mostly due to their exceptionally high diversity and ultra-fast rates of phenotypic divergence (Meyer et al., 1990;Kocher, 2004;Genner & Turner, 2005;Henning & Meyer, 2014). Cichlids famously vary in morphological traits, such as body coloration and their trophic morphology, but also in behavioral traits, such as social systems and parental care (Meyer, 1993;Seehausen, 1997;Stiassny & Meyer, 1999;Wisenden et al., 2015). ...
Cichlid fishes’ famous diversity in body coloration is accompanied by a highly diverse and complex visual system. Although cichlids possess an unusually high number of seven cone opsin genes, they express only a subset of these during their ontogeny, accounting for their astonishing interspecific variation in visual sensitivities. Much of this diversity is thought to have been shaped by natural selection as cichlids inhabit a variety of habitats with distinct light environments. Also, sexual selection might have contributed to the observed visual diversity, and sexual dimorphism in coloration potentially co‐evolved with sexual dimorphism in opsin expression. We investigated sex‐specific opsin expression of several cichlids from Africa and the Neotropics and collected and integrated datasets on sex‐specific body coloration, species‐specific visual sensitivities, lens transmission and habitat light properties for some of them. We comparatively analyzed this wide range of molecular and ecological data, illustrating how integrative approaches can address specific questions on the factors and mechanisms driving diversification, and the evolution of cichlid vision in particular. We found that both sexes expressed opsins at the same levels ‐ even in sexually dimorphic cichlid species – which argues against coevolution of sexual dichromatism and differences in sex‐specific visual sensitivity. Rather, a combination of environmental light properties and body coloration shaped the diversity in spectral sensitivities among cichlids. We conclude that although cichlids are particularly colorful and diverse and often sexually dimorphic, it would appear that natural rather than sexual selection is a more powerful force driving visual diversity in this hyper‐diverse lineage.
... Human activities linked to urbanization and intensive agriculture can lead to increased eutrophication and water turbidity (Bonsdorff et al., 1997). Water turbidity can strongly interfere with visual signals in freshwater fish (Seehausen et al., 1997(Seehausen et al., , 2008Jarvenpaa & Lindstrom, 2004;Genner & Turner, 2005) because visual signals can be reduced due to a lack of visibility in such habitats. For instance, in Lake Victoria Neochromis cichlids, eutrophication led to a decrease in colour diversity which impacted mate choice and reproductive isolation (Seehausen et al., 1997). ...
Human activities cause rapid eutrophication and increased water turbidity in aquatic ecosystems, but their effects on fish communication and colour signals remain of debate. In particular, melanin-based coloration in fish has been understudied, because it was believed to be less costly to display than carotenoid-based colours. Here, we measured the phenotypic divergence of melanin-based coloration in 17 populations of gudgeon (Gobio occitaniae) along a turbidity gradient. We also tested the short-term plasticity of coloration using a reciprocal transplant experiment. We found strong variability in melanin-based coloration along the turbidity gradient: interpopulation divergence in coloration was higher than predicted by genetic drift, and fish were paler with increasing levels of turbidity. Finally, a reciprocal transplant experiment revealed that fish transplanted into more turbid habitats expressed a paler melanin-based coloration, suggesting that melanin-based coloration was highly plastic in the short term. Overall, our results suggest that eutrophication in human-altered rivers can rapidly alter melanin-based coloration, with potential consequences for fish visual communication and sexual selection.
... R. Soc. B 286: 20182358 than 2 Myr to feed from a diversity of similar ecological substrates [47,48]. Both groups have members that exploit plankton in the open water and that feed from the algal mats that cover rocky outcrops found throughout the Lake [30,49]. ...
Complexity in how mechanistic variation translates into ecological novelty could be critical to organismal diversification. For instance, when multiple distinct morphologies can generate the same mechanical or functional phenotype, this could mitigate trade-offs and/or provide alternative ways to meet the same ecological challenge. To investigate how this type of complexity shapes diversity in a classic adaptive radiation, we tested several evolutionary consequences of the anterior jaw four-bar linkage for Lake Malawi cichlid trophic diversification. Using a novel phylogenetic framework, we demonstrated that different mechanical outputs of the same four jaw elements are evolutionarily associated with both jaw protrusion distance and jaw protrusion angle. However, these two functional aspects of jaw protrusion have evolved independently. Additionally, although four-bar morphology showed little evidence for attraction to optima, there was substantial evidence of adaptive peaks for emergent four-bar linkage mechanics and jaw protrusion abilities among Malawi feeding guilds. Finally, we highlighted a clear case of two cichlid species that have independently evolved to graze algae in less than 2 Myr and have converged on similar jaw protrusion abilities as well as four-bar linkage mechanics, but have evolved these similarities via non-convergent four-bar morphologies. © 2019 The Author(s) Published by the Royal Society. All rights reserved.
... The repeated evolution of hypertrophied lips across both a diversity of teleosts as well as its presence within numerous phylogenetically disparate cichlid lineages suggests that the hypertrophied lip lineages in Lake Malawi could have evolved convergently. With approximately 1000 species of haplochromine cichlids, the opportunity for the repeated origin of adaptive traits within the Malawi radiation is extensive [38][39][40]. Also, Malawi species with hypertrophied lips are currently classified into several different genera based in part on their extensive differences in body pigment patterns [27,[41][42][43][44]. ...
Background
Phylogenies provide critical information about convergence during adaptive radiation. To test whether there have been multiple origins of a distinctive trophic phenotype in one of the most rapidly radiating groups known, we used ultra-conserved elements (UCEs) to examine the evolutionary affinities of Lake Malawi cichlids lineages exhibiting greatly hypertrophied lips.
Results
The hypertrophied lip cichlids Cheilochromis euchilus, Eclectochromis ornatus, Placidochromis “Mbenji fatlip”, and Placidochromis milomo are all nested within the non-mbuna clade of Malawi cichlids based on both concatenated sequence and single nucleotide polymorphism (SNP) inferred phylogenies. Lichnochromis acuticeps that exhibits slightly hypertrophied lips also appears to have evolutionary affinities to this group. However, Chilotilapia rhoadesii that lacks hypertrophied lips was recovered as nested within the species Cheilochromis euchilus. Species tree reconstructions and analyses of introgression provided largely ambiguous patterns of Malawi cichlid evolution.
Conclusions
Contrary to mitochondrial DNA phylogenies, bifurcating trees based on our 1024 UCE loci supported close affinities of Lake Malawi lineages with hypertrophied lips. However, incomplete lineage sorting in Malawi tends to render these inferences more tenuous. Phylogenomic analyses will continue to provide powerful inferences about whether phenotypic novelties arose once or multiple times during adaptive radiation.
Electronic supplementary material
The online version of this article (10.1186/s12862-018-1296-9) contains supplementary material, which is available to authorized users.
... Cichlid fishes are evolutionary model organisms for studying the process of speciation, mostly due to their exceptionally high diversity and fast rate of phenotypic divergence (Kocher 2004;Genner & Turner 2005;. Cichlids famously vary in morphological traits, such as body coloration and their trophic morphology, but also in behavioral traits such as parental care (Seehausen 1997;Wisenden et al. 2015). ...
... Among fishes, cichlids (Teleostei: Cichlidae) are well known for their success at modifying a suction-based craniofacial theme in order to invade a diversity of trophic niches (Stiassny 1981;Winemiller et al. 1995;Muschick et al. 2012). The value of these species as a model group for understanding adaptive radiations is widely appreciated (Genner and Turner 2005;Seehausen 2006;Muschick et al. 2014), with multiple lineages displaying recent and rapid bouts of diversification (Burress and Tan 2017). In the present work, we focus on the morphologically and trophically diverse cichlids of the East African rift lakes, Tanganyika and Malawi. ...
The fish feeding apparatus is among the most diverse functional systems in vertebrates. While morphological and mechanical variation of feeding systems are well studied, we know far less about the diversity of the motions that they produce. We explored patterns of feeding movements in African cichlids from Lakes Malawi and Tanganyika, asking whether the degree of kinesis is associated with dietary habits of species. We used geometric morphometrics to measure feeding kinesis as trajectories of shape change, based on 326 high‐speed videos in 56 species. Cranial morphology was significantly related to feeding movements, both of which were distributed along a dietary axis associated with prey evasiveness. Small‐mouthed cichlids that feed by scraping algae and detritus from rocks had low kinesis strikes, while large‐mouthed species that eat large, evasive prey (fishes and shrimps) generated the greatest kinesis. Despite having higher overall kinesis, comparisons of trajectory shape (linearity) revealed that cichlids that eat mobile prey also displayed more kinematically conserved, or efficient, feeding motions. Our work indicates that prey evasiveness is strongly related to the evolution of cichlid jaw mobility, suggesting that this same relationship may explain the origins and diversity of highly kinetic jaws that characterize the super‐radiation of spiny‐rayed fishes.
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... Adaptive radiation is often invoked to explain the species diversification in the Cichlidae as in the East African cichlid species characterized by ecomorphological and colour variations (e.g. [97][98][99][100]) or in the Neotropical crater lake (e.g. [101][102][103][104]) and riverine [50,[105][106] cichlids. ...
Evaluating biodiversity and understanding the processes involved in diversification are noticeable conservation issues in fishes subject to large, sometimes illegal, ornamental trade purposes. Here, the diversity and evolutionary history of the Neotropical dwarf cichlid genus Apistogramma from several South American countries are investigated. Mitochondrial and nuclear markers are used to infer phylogenetic relationships between 31 genetically identified species. The monophyly of Apistogramma is suggested, and Apistogramma species are distributed into four clades, corresponding to three morphological lineages. Divergence times estimated with the Yule process and an uncorrelated lognormal clock dated the Apistogramma origin to the beginning of the Eocene (≈ 50 Myr) suggesting that diversification might be related to marine incursions. Our molecular dating also suggests that the Quaternary glacial cycles coincide with the phases leading to Apistogramma speciation. These past events did not influence diversification rates in the speciose genus Apistogramma, since diversification appeared low and constant through time. Further characterization of processes involved in recent Apistogramma diversity will be necessary.
... Reef-dwelling lineages might only rarely or never produce species that evolve to colonize other habitats. For instance, the mbuna constitute a putatively monophyletic group of approximately 400 cichlid species that could only inhabit the rocky shores of Lake Malawi (Ribbink et al., 1983;Genner et al., 2004;Genner and Turner, 2005). The habitat complexity that characterizes the rocky shores of Lake Malawi provides rich opportunities for niche partitioning and trophic specialization, and the mbuna do dominate and extensively exploit this habitat (MacArthur and Levins, 1964;Schoener, 1974;Ribbink et al., 1983; but see Martin and Genner, 2009). ...
Adaptive radiations could often occur in discrete stages. For instance, the species flock of ∼1000 species of Lake Malawi cichlid fishes might have only diverged once between rocky and sandy environments during the initial stage of their diversification. All further diversification within the rock-dwelling (mbuna) or sand-dwelling (utaka) cichlids would have occurred during a subsequent second stage of extensive trophic evolution that was followed by a third stage of sexual trait divergence. We provide an improved phylogenetic framework for Malawi cichlids to test this three-stage hypothesis based on newly reconstructed phylogenetic relationships among 32 taxonomically disparate Malawi cichlids species. Using several reconstruction methods and 1037 ultra-conserved element (UCE) markers, we recovered a molecular phylogeny that confidently resolved relationships among most of the Malawi lineages sampled when a bifurcating framework was enforced. These bifurcating reconstructions also indicated that the sand-dwelling species Cyathochromis obliquidens was well-nested within the primarily rock-dwelling radiation known as the mbuna. In contrast to predictions from the three-stage model of vertebrate diversification, the recovered phylogeny reveals an initial colonization of rocky reefs, followed by substantial diversification of rock-dwelling lineages, and then at least one instance of subsequent evolution back into sandy habitats. This repeated evolution into major habitat types provides further evidence that the three-stage model of Malawi cichlid diversification has numerous exceptions.
... Water level fluctuations have repeatedly re-structured the marine littoral as well as the littoral of large ancient lakes, but in many aquatic species, planktonic larval dispersal prevents population isolation (Cheang et al. 2012;Koblm€ uller et al. 2015). Mouth-brooding interferes with larval dispersal in Tropheus and many other stenotopic rock dwellers in Lakes Malawi and Tanganyika, many of which display pronounced allopatric colour pattern variation among eco-morphologically undifferentiated populations (Konings 1998;Genner & Turner 2005;Maan & Sefc 2013). Lake level fluctuations have been proposed as drivers of diversity among lacustrine cichlids by splitting formerly continuous populations (Rossiter 1995) or generating ecological opportunities (Winkelmann et al. 2017). ...
The establishment of hybrid taxa relies on reproductive isolation from the parental forms, typically achieved by ecological differentiation. Here, we present an alternative mechanism, in which shifts in the strength and location of dispersal barriers facilitate diversification by hybridisation. Our case study concerns the highly diverse, stenotopic rock-dwelling cichlids of the African Great Lakes, many of which display geographic colour pattern variation. The littoral habitat of these fish has repeatedly been restructured in the course of ancient lake level fluctuations. Genetic data and an experimental cross support the hybrid origin of a distinct yellow-coloured variant of Tropheus moorii from ancient admixture between two allopatric, red and bluish variants. Deficient assortative mating preferences imply that reproductive isolation continues to be contingent on geographic separation. Linking paleolimnological data with the establishment of the hybrid variant, we sketch a selectively neutral diversification process governed solely by rearrangements of dispersal barriers.
... This stands in contrast to many other classic adaptive radiations like Darwin's Finches or Anolis lizards wherein it is relatively rare to find more than Scientific RepoRts | 7:40306 | DOI: 10.1038/srep40306 ten species together and most of these likely cannot form viable hybrids 53,54 . Additionally, a substantial diversity of the Lake Malawi radiation is made up of the rock-dwelling mbuna, cichlids that can be endemic to the rocky outcrops ringing individual islands 55 . Because water levels in Lake Malawi have changed extensively over time and repeatedly created new island habitats 56 , individual mbuna colonizing these islands might commonly be left with no reproductive option but to hybridize with other species. ...
Hybrid phenotypes are often intermediate between those of parental species. However, hybridization can generate novel phenotypes when traits are complex. For instance, even when the morphologies of individual musculo-skeletal components do not segregate outside the parental range in hybrid offspring, complex functional systems can exhibit emergent phenotypes whose mechanics exceed the parental values. To determine if transgression in mechanics could facilitate divergence during an adaptive radiation, we examined three functional systems in the trophic apparatus of Lake Malawi cichlid fishes. We conducted a simulation study of hybridization between species pairs whose morphology for three functional systems was empirically measured, to determine how the evolutionary divergence of parental species influences the frequency that hybridization could produce mechanics that transgress the parental range. Our simulations suggest that the complex mechanical systems of the cichlid trophic apparatus commonly exhibit greater transgression between more recently diverged cichlid species. Because (1) all three mechanical systems produce hybrids with transgressive mechanics in Lake Malawi cichlids, (2) hybridization is common, and (3) single hybrid crosses often recapitulate a substantial diversity of mechanics, we conclude that mechanical transgressive segregation could play an important role in the rapid accumulation of phenotypic variation in adaptive radiations.
... Suggestions in the 1970s to introduce Limnothrissa spp into Lake Malawi to fill a 'vacant niche' occupied by the insect Chaoborus edulis (Degnbol, 1990) were shown by later detailed investigations to have posed a high risk to the lake food web and fisheries (Irvine et al., 2001;Darwall et al., 2010). At a smaller scale, internal translocations of cichlids within Lake Malawi as a consequence of the ornamental fish trade have been shown to disrupt genetic sorting and integrity of localized endemic populations associated with rocky outcrops (Genner and Turner, 2005). As the world enters uncharted territory with respect to climate shifts, preserving the rich endemic communities of tropical aquatic systems offers possibilities not only for better overall understanding of adaptation of tropical aquatic communities, but a pool of species that can be an ecological buffer to ecosystem disruption. ...
1. Tropical aquatic ecosystems are species rich, with high numbers of endemics. Increasing pressure from human activities, including demands for food and energy, growing human population, and economic aspirations, highlights the need for a more concerted effort towards aquatic conservation.
2. Understanding of tropical aquatic ecosystems has developed largely from a northern temperate perspective that might not be always appropriate. Applying classic models of how water bodies function can hinder effective conservation strategies. This is coupled with very incomplete knowledge of species distributions and their ecology.
3. Better understanding of tropical aquatic ecology to guide conservation needs a research agenda that connects more strongly with the social‐ecological realities of tropical ecosystems.
4. Although approaches to conservation may be contested, a fundamental challenge to protection of aquatic habitats is a lack of capacity at the individual and institutional level. Without this, the development of improved techniques and approaches for tropical aquatic conservation will fail to reverse current trends of degradation. Research outputs on tropical aquatic ecosystems remain dominated by institutions based outside the tropics.
5. Building awareness and practice to conserve the aquatic ecosystems of the tropics can be supported through extending the dialogue across sectors and by connecting tiers of governance. An ecosystem services framework that identifies the benefits that humans derive from ecosystems provides a powerful tool, often linked with estimates of economic value. However, this can neglect important regulating services or distract from more fundamental existence value.
6. The preservation of tropical aquatic diversity will only be achieved if recognized as important at all levels, from local to global. Targeted external support can build awareness and capacity, but conserving aquatic ecosystems requires local commitment. Developing community monitoring that provides straightforward information on ecosystem health presents opportunities to connect citizens with the ecosystems that, ultimately, they depend on. Copyright © 2016 John Wiley & Sons, Ltd.
... Clariidae (e.g., Clarias batrachus) and Anabantidae (e.g., Anabas cobojius). Taken as a whole, the adaptive radiation of cichlids in each African Rift Lake constitutes an example of repeated radiation (Kocher 2004, Genner and Turner 2005, Salzburger et al. 2005, Young et al. 2009, Cooper et al. 2010) when convergences can also occur within a single adaptive radiation (Muschick et al. 2012). Replicate divergences of benthic and limnetic forms of sticklebacks in Holarctic postglacial lakes are additional examples of repeated radiations (Cooper et al. 2010). ...
Damselfishes (Pomacentridae) are highly conspicuous, diurnal inhabitants of mainly reef areas, capturing the attention of many scientists. Their high diversity and many interesting characteristics dealing with their way of life (sound production, breeding biology, sex change, farming and gregarious behavior, settlement, diet, habitat) easily explain this group is continually kept in the limelight and is the subject of numerous studies. This book gathers the data dealing with damselfish morphology, physiology, behavior, ecology and phylogeny. It contains 14 chapters written by renowned scientists.
... Clariidae (e.g., Clarias batrachus) and Anabantidae (e.g., Anabas cobojius). Taken as a whole, the adaptive radiation of cichlids in each African Rift Lake constitutes an example of repeated radiation (Kocher 2004, Genner and Turner 2005, Salzburger et al. 2005, Young et al. 2009, Cooper et al. 2010) when convergences can also occur within a single adaptive radiation (Muschick et al. 2012). Replicate divergences of benthic and limnetic forms of sticklebacks in Holarctic postglacial lakes are additional examples of repeated radiations (Cooper et al. 2010). ...
Ecological morphology is a comparative discipline focused on the connections between morphological and ecological diversity. The ecomorphological approach examines the optimization of functional morphology to specific ecological characters at multiple levels: among individuals within a species, among species and higher taxa, and among guilds and communities. Such examinations of the causative connections between form, function and ecology represent an important and a relevant framework for addressing. In this chapter, we describe the ecomorphological diversity of the Pomacentridae and discuss the adaptive significance of specific aspects of their functional morphology of feeding and swimming. We also report morphological variation among populations of various species within the context of local adaptation and/or plasticity. At the family level, we discuss the reticulated pattern of evolutionary diversification in damselfish ecomorphology as revealed by the use of modern phylogenetic comparative methods. The chapter concludes with some perspectives regarding the study of ecomorphology in the Pomacentridae.
... The mostly rocky shore-dwelling subunit of the flock, known as the mbuna, has itself been inferred to be monophyletic by some workers based on both gestalt (Trewavas 1935;Fryer and Iles 1972:493) and weak evidence from molecular systematics (conflicting studies summarized by Genner and Turner 2005). However, Oliver and Arnegard (2010) showed that none of the anatomical characters proposed by various authors as supporting the monophyly of the mbuna can be substantiated as a synapomorphy. ...
A downward kink one or more scales in length at the posterior end of the upper lateral line, leaving only one scale row instead of two between it and the lower lateral line, has been considered a synapomorphy uniting as a monophyletic group all members of both clades of endemic haplochromine cichlids of Lake Malaŵi. Here, this claim is tested by surveying the character in representatives of all genera of Lake Malaŵi haplochromines (tribe Haplochromini of the subfamily Pseudocrenilabrinae). Presence of the kink is shown to be variable in most genera, and it was not documented at all in two (Abactochromis, Cyrtocara). Specimens with no kink occur in many genera, and kink presence and length frequently vary on the two sides of the body. Thus, it is difficult to justify the kink as a synapomorphy of the species flock. The two clades differ in kink frequency; a kink occurred on at least one side of the body in 79% of bilaterally assessable specimens in the non-mbuna clade, but in only 53% of those in the mbuna clade (p < 0.0001). When a kink is present, its length is more variable in non-mbuna (1 to 8 scales, mode 2) than mbuna (1 to 4 scales, mode 1). Extension of the upper lateral line backward from the upper flank close to or onto the caudal peduncle, where no scale row is as dorsally situated, is identified as one cause of kink existence; additional factors likely await discovery. Contrary to published statements, the kink is expressed in some specimens of Astatotilapia calliptera, a phylogenetically important nonendemic haplochromine found in Lake Malaŵi and elsewhere, which may be the sister of the lake's endemic flock. An apparently identical lateral-line kink occurs sporadically in haplochromines in other lakes and in members of three other pseudocrenilabrine cichlid tribes, further refuting the hypothesis that this character is a synapomorphy of the Lake Malaŵ i species flock. © 2016 Peabody Museum of Natural History, Yale University. All rights reserved.
... Cichlids represent the most species-rich group of Perciformes, and indeed all vertebrates, and comprise more than 3000 living species (Nelson 2006). The African continent has the greatest number of species (more than 1500) and the highest diversity in this family is found in the Great Lakes of East Africa (Victoria, Tanganyika, and Malawi) (Trewavas 1983;Genner and Turner 2005). For instance, approximately 500 species of cichlids that colonized Lake Victoria have evolved from only a few ancestral species in the last 100 000 years (Verheyen et al. 2003). ...
The genomic loci generating both adaptive and maladaptive variation could be surprisingly predictable in deeply homologous vertebrate structures like lips. Variation in highly conserved vertebrate traits such as jaws and teeth in organisms as evolutionarily disparate as teleost fishes and mammals are known to be structured by the same genes. Likewise, hypertrophied lips that have evolved repeatedly in Neotropical and African cichlid fish lineages could share unexpectedly similar genetic bases themselves and even provide surprising insight into the loci underlying human craniofacial anomalies. To isolate the genomic regions underlying adaptive divergence in hypertrophied lips, we first employed genome wide associations (GWA) in several species of African cichlids from Lake Malawi. Then, we tested if these GWA regions were shared through hybridization with another Lake Malawi cichlid lineage that has evolved hypertrophied lips seemingly in parallel. Overall, introgression among hypertrophied lip lineages appeared limited. Among our Malawi GWA regions, one contained the gene kcnj16 that has been implicated in the convergently evolved hypertrophied lips in Central American Midas cichlids that diverged from the Malawi radiation over 50 million years ago. The Malawi hypertrophied lip GWA regions also contained several additional genes that cause human lip-associated birth defects. Cichlid fishes are becoming prominent examples of replicated genomic architecture underlying trait convergence and are increasingly providing insight into human craniofacial anomalies such as cleft lip.
Sexual selection has been shown to drive speciation. In dwarf spiders (erigonines), males possess diverse, sexually selected prosomal structures with nuptial-gift-producing glands. The genus Oedothorax is suitable for investigating the evolution of these features due to high structural variation. We have re-delimited this genus based on a phylogenetic analysis. Ten species are Oedothorax s.s.; five are transferred back to their original generic placement; 25 remain unplaced as ‘Oedothorax’. Four junior synonymies are proposed: Callitrichia simplex to Ca. holmi comb. nov.; Gongylidioides kougianensis to G. insulanus comb. nov.; Ummeliata ziaowutai to U. esyunini comb. nov.; Oe. kathmandu to Mitrager unicolor comb. nov. Oedothorax seminolus is a junior synonym of Soulgas corticarius and the transfer of Oe. alascensis to Halorates is confirmed. The replacement name Ca. hirsuta is proposed for Ca. pilosa. The male of Callitrichia longiducta comb. nov. and the female of ‘Oedothorax’ nazareti are newly described. Thirty-eight Oedothorax species are transferred to other genera. Callitrichia spinosa is transferred to Holmelgonia. Three genera are erected: Cornitibia, Emertongone and Jilinus. Ophrynia and Toschia are synonymized with Callitrichia. Character optimization suggests multiple origins of different prosomal modification types. Convergent evolution in these traits suggests that sexual selection has played an important role in erigonine diversification.
Increasing evidence suggests that there are diverse types of evolutionary radiation, yet there is no widely accepted method to classify them. An article by Matsubayashi and Yamaguchi in the current issue of Population Ecology proposes a new method to define adaptive and non‐adaptive radiation, which may also provide a clue to the classification of evolutionary radiations. In this commentary, I discuss how should we classify evolutionary radiations in order to facilitate our understanding of them.
The adaptive genetic variation in response to heterogeneous habitats of the Indian Ocean was investigated in the Indian oil sardine using ddRAD sequencing to understand the subpopulation structure, stock complexity, mechanisms of resilience, and vulnerability in the face of climate change. Samples were collected from different ecoregions of the Indian ocean and ddRAD sequencing was carried out. Population genetic analyses revealed that samples from the Gulf of Oman significantly diverged from other Indian Ocean samples. SNP allele-environment correlation revealed the presence of candidate loci correlated with the environmental variables like annual sea surface temperature, chlorophyll- a , and dissolved oxygen concentration which might represent genomic regions allegedly diverging as a result of local adaptation. Larval dispersal modelling along the southwest coast of India indicated a high dispersal rate. The two major subpopulations (Gulf of Oman and Indian) need to be managed regionally to ensure the preservation of genetic diversity, which is crucial for climatic resilience.
The complex social behaviour of cichlids has fascinated scientists and hobbyists alike for almost 100 years. In this chapter, we review the breadth and complexity of cichlid behaviour, particularly with respect to social interactions. We present the case that cichlids are one of the best model systems for understanding both the mechanisms and evolution of behaviour. This is due to the fact that cichlids can be observed without being greatly disturbed, both in the aquarium and field and because of the unique opportunity to experimentally manipulate their environment and behaviour. We first give a brief account of the diversity of social systems in the cichlids and the diverse research in this area, from the very early work of authors like Curtis, Noble, and Baerends, to modern studies into the dynamics and structure of social behaviour in these fish. In Sect. 2, we explore the causal factors leading to the evolution of social complexity, discussing the occurrence and evolution of different social systems across ecological and life-history contexts. We investigate the behavioural complexity displayed by cichlids in Sect. 3, including a brief treatment of the different modalities of behavioural interactions. In Sect. 4, we discuss the immense potential for using cichlids as model species in studying social and behavioural evolution, before ending in Sect. 5 with exciting future directions for research employing the latest technical advances in both the laboratory and field.
The Iquitos Paleoarch is decisive for the restricted distribution of many Apistogramma species in the region. Distinguishing it from large parts of the Amazonian basin, only few seasonal rhythmic inundations trigger frequent isolation events and create a setting favourable for diversification and speciation. Iquitos, probably the fastest expanding city in Amazonia, is located within the Iquitos Paleoarch. Here local resource harvesting frequently leads to small-scale deforestation. Simultaneously, the forest plays a decisive role in the aquatic ecology of streams and ponds by regulating the temperature regime and providing dead plant material, resulting in low pH and conductivity levels, properties typical of blackwater. We conducted field measurements of water parameters in selected areas inhabited by Apistogramma atahualpa. Our results show that the temperature regime varies widely in streams and ponds, and temperature increases are especially abrupt at the transition from forested habitats to deforested, open areas. We elaborate how this effect of small-scale deforestation and associated temperature change can impact the breeding biology of A. atahualpa. Due to all Apistogramma species studied so far exhibiting temperature-dependent sex determination (TSD) of offspring, we anticipate changes in population structure following such abrupt alterations in ecological conditions of aquatic habitats. Additional isolation events typical for this region may further impact populations and induce diversification. Our findings highlight the need for more detailed assessments of the impact of deforestation and other ecological alterations on blackwater habitats at small spatial scales, as they can pose a serious threat to many aquatic species.
Background:
The diversification process known as the Lake Tanganyika Radiation has given rise to the most speciose clade of African cichlids. Almost all cichlid species found in the lakes Tanganyika, Malawi and Victoria, comprising a total of 12-16 tribes, belong to this clade. Strikingly, all the species in the latter two lakes are members of the tribe Haplochromini, whose origin remains unclear. The 'out of Tanganyika' hypothesis argues that the Haplochromini emerged simultaneously with other cichlid tribes and lineages in Lake Tanganyika, presumably about 5-6 million years ago (MYA), and that their presence in the lakes Malawi and Victoria and elsewhere in Africa today is due to later migrations. In contrast, the 'melting pot Tanganyika hypothesis' postulates that Haplochromini emerged in Africa prior to the formation of Lake Tanganyika, and that their divergence could have begun about 17 MYA. Haplochromine fossils could potentially resolve this debate, but such fossils are extremely rare.
Results:
Here we present a new fossil haplochromine from the upper Miocene site Waril (9-10 million years) in Central Kenya. Comparative morphology, supported by Micro-CT imaging, reveals that it bears a unique combination of characters relating to dentition, cranial bones, caudal skeleton and meristic traits. Its most prominent feature is the presence of exclusively unicuspid teeth, with canines in the outer tooth row. †Warilochromis unicuspidatus gen. et sp. nov. shares this combination of characters solely with members of the Haplochromini and its lacrimal morphology indicates a possible relation to the riverine genus Pseudocrenilabrus. Due to its fang-like dentition and non-fusiform body, †W. unicuspidatus gen. et sp. nov. might have employed either a sit-and-pursue or sit-and-wait hunting strategy, which has not been reported for any other fossil haplochromine cichlid.
Conclusions:
The age of the fossil (9-10 MYA) is incompatible with the 'out of Tanganyika' hypothesis, which postulates that the divergence of the Haplochromini began only 5-6 MYA. The presence of this fossil in an upper Miocene palaeolake in the Central Kenya Rift, as well as its predatory lifestyle, indicate that Haplochromini were already an important component of freshwater drainages in East Africa at that time.
Fish respond to their “reproductive duty” and their reproductive needs by adopting a large diversity of adaptive behaviors in relation to constraints exerted by environmental conditions. Most spawners abandon their offspring and return to their feeding habitats. The reproductive scenario can be broadly divided into four major phases: an anticipatory phase, a preparatory or pre‐spawning phase, a phase of realization or spawning, and a terminal or postspawning phase. The partners of both sexes, having made the effort to promote themselves and to display their qualities, owe it to themselves to reap the benefits and to carry out couplings which promise beautiful reproductive success as quickly as possible. Reproductive migrations involve movements of spawners of varied magnitude and variable duration according to the species. Most species practice large sexual freedom with frequent changes of partners, which offers the advantage of a large mixing of genes inducing a large genetic diversity that is beneficial to the population.
Cichlid fishes in the rocky littoral zones of Lake Malawi are among the most diverse endemic fish communities of the world. They segregate food resources, but considerable niche overlaps have been reported by numerous studies in this field. If their niches largely overlap, the heterospecific individuals are expected to behave like conspecific individuals. Instead of studying their niche segregation, we investigated the spatial distribution patterns of adult males of nine abundant cichlid species by point process analysis, with due attention to niche partitioning, as measured by stable isotope analysis. Because their feeding habitats are restricted by intra‐ and interspecific interferences over the mating and feeding territories respectively, we hypothesised that the interspecific feeding territories of species with nearly similar niche tended to be distributed uniformly. Although the typical territorial animals are expected to be distributed uniformly, the distribution pattern of intraspecific mating territory was judged to be uniform only for two out of nine species. This result suggests that each species has its specific preference for territorial locations or their locations are restricted by interspecific interactions. The latter explanation was partially supported by the agreed locations of gravity centres between intraspecific mating and interspecific feeding territories. Species pairs with similar isotope ratios tended to show a uniform distribution of interspecific feeding territories. Thus, individual species pairs keep a certain distance from each other by using nearly similar food resources. This result suggests that some cichlid species coexist not only through niche segregation but also through territorial interactions, like conspecific individuals.
Declines in fish yields and shifts in species composition are serious concerns in the African Great lakes of Tanganyika, Malawi (Nyasa/Niassa) and Victoria. Despite management and regulatory structures, all the lakes remain open‐access fisheries, severely depressing yields, economic returns and threatening biodiversity. While the lakes require an ecosystem‐based approach to management, this has not been realised because of a lack of institutional capacities, insufficient political will or simply being overwhelmed by the scale of the endeavour. Sustainable fisheries management can only be achieved through a refocus towards a stronger socio‐ecological approach and re‐evaluating how to realistically improve fish yield and environmental protection. This requires a combination of the following: (1) acceptance of suboptimal fish yields; (2) community‐enforced regulations that restrict access to fisheries and destruction of inshore habitats; (3) enhanced national and local institutional capacities and collaboration among the riparian states; and (4) major awareness and educational efforts that demonstrate the national and international importance of these lakes for food supply and biodiversity in pursuance of the Sustainable Development Goals. Without such actions, the prognosis for long‐term sustainable fisheries is bleak, and international projects and conferences will merely bear witness to further degradation of resources and the livelihoods they support.
A reexamination of the type specimens of the cichlid genera Cynotilapia and Microchromis from Lake Malawi is given, revealing significant differences between them, and confirming the validity of Microchromis. Microchromis zebroides, type species of the genus, is reexamined with additional material. Microchromis aurifrons, a new species is described. It differs from the type species of the genus, with which it lives sympatrically in the lake, by wider melanic pattern on the flanks and absence of such coloration on the brow of adults. The distinction between Cynotilapia and Microchromis and the relationships with the bicuspid-toothed genus Maylandia, of which Microchromis is possibly a plankton-eater specialized offshoot, are debated.
A new genus, Metriaclima, is described for members of the Pseudotropheus zebra complex from Lake Malaŵi. The presence of bicuspid teeth in the anterior portion of the outer row of both the upper and lower jaws distinguishes Metriaclima from many of the previously described genera of rock-dwelling cichlids that inhabit Lake Malaŵi, including Cyathochromis, Cynotilapia, Gephyrochromis, Labidochromis, and Petrotilapia. The absence of two horizontal stripes along its flanks, distinguishes it from Melanochromis. The isognathous jaws of Metriaclima delimits it from Genyochromis, which is characterized by having the lower jaw extend in front of the upper jaw. The mouth of Metriaclima is terminal, while that of Labeotropheus is inferior. Within the genus Pseudotropheus as it is now recognized, species of Metriaclima are unique because they have a moderately sloped ethmo-vomerine block and a swollen rostral tip. Ten previously undescribed species that have a slight variation from the characteristic blue/black barring are described. The new species are recognized primarily by their distinctive adult coloring in conjunction with the discontinuity of morphological differences throughout their range.
Molecular genetic variation was examined within and among species of the rock-dwelling cichlid fishes (mbuna) of Lake Malawi. Phylogenetic relationships among mbuna mitochondrial DNA (mtDNA) haplotypes were estimated by using restriction-fragment-length polymorphisms. The distribution of these lineages among mbuna species is of particular significance for phylogenetic systematic study of this fauna. Some species were found to be polymorphic for divergent haplotypes that substantially predate their isolation from sister taxa. Repeated speciation events among numerous closely related taxa appear to have been so recent that mtDNA lineage sorting among species is incomplete. Thus, the mtDNA gene tree is not congruent with the putative species tree. These results indicate that analysis of mtDNA alone will not be sufficient for resolution of phylogenetic relationships in the mbuna. Clarification of these relationships will require examination of multiple nuclear loci, because many of these new markers are also likely to retain ancestral polymorphisms.
A new species of the cichlid fish genus Pseudotropheus from Lake Malawi, Africa, is described. The new species superficially resembles Pseudotropheus lanisticola and P. livingstonii, but is clearly distinguished by head shape. The behavior pattern of cleaning ectoparasites from other cichlids is unique among all known species of Pseudotropheus.
Courtship sounds made by three sympatric cichlid species, Pseudotropheus zebra, P. callainos and an undescribed species known as P. ‘zebra gold’ were recorded and compared to investigate the potential role of acoustic signals in mate choice. Sounds were emitted during ‘quiver’ and ‘circle’ components of the male courtship display and consisted of rapidly repeated pulse units. Some sound variables differed significantly among species with P. callainos generally being separated from the other two species. This species produced sounds with higher peak frequency (for a given length) and lower number of pulses than P. ‘zebra gold’ and higher pulse durations than P. zebra. In addition, standard length was inversely related to peak frequency in both P. ‘zebra gold’ and P. callainos(this relation was not tested in P. zebra due to the small sample size). These differences might indicate different regimes of intraspecific sexual selection among the three species.
The genotypes of two microsatellite loci were determined for the mouthbrooded progeny of 13 females, representing seven species of both rock- and sand-dwelling Lake Malawi cichlid fishes. Multiple paternity is clearly demonstrated for all but two broods. One brood contained the progeny of at least six males. Heterozygosity of these two microsatellite loci in a sample of 18 male Copadichromis cyclicos was 89% and 83%, respectively. Each locus displayed 16 alleles among the 18 males. The expected average exclusion probability using both loci, given a mother/offspring pair, is 0.968, suggesting that microsatellite variation will be useful for quantifying mate choice in these taxa. The low heterozygosity of a Melanochromis auratus brood is consistent with reduced levels of mtDNA polymorphism previously documented in this species. Thus microsatellite variation may provide insight into the genetic history of these populations.
p>The presented thesis focuses on three members of the Pseudotropheus (Maylandia) complex: shallow-dwelling rock-frequenting cichlids of the mbuna group. These species differ primarily in male breeding coloration. Experiments were conducted on these taxa to address one of the key questions in relation to evolution via sexual selection: what maintains reproductive isolation between closely related sympatric dwelling forms? It was demonstrated that males cannot visually distinguish conspecific females but a study determining parentage using microsatellite loci found that reproductive isolation between the three taxa is nonetheless maintained without exception in the artificial confines of aquaria. This provides indirect evidence for reproductive isolation by direct mate choice and suggests that females may play a more important role in mate recognition than males. An analysis of morphometric data also identified potential male secondarily sexually selected traits. This information is likely to be of use of future studies investigating the cues females may be using to choose spawning partners.
Within-population dispersal, another important parameter on which no data have hitherto been available, was addressed here using microsatellite molecular markers to statistically estimate pairwise relatedness, which was in turn correlated with pairwise geographic distance. The results of this study were highly suggestive of male-biased dispersal. Male-biased dispersal is more conductive to speciation under recently proposed sexual selection models than is female-biased dispersal. Further, knowledge of small-scale dispersal takes the field closer to a comprehensive understanding of the population dynamics of these species.
The three Pseudotropheus species studied show colour polymorphism. Although males are almost all of one morph, two or three morphs are common in females. A field survey recording morph frequencies along with a study of the genetical inheritance of these morphs was undertaken in an attempt to clarify previously unresolved issues concerning the possible adaptive and/or evolutionary significance of these morphs.</p
Annual cycles of breeding activity were found in 10 species of rock‐frequenting cichlid fishes endemic to Lake Malawi. Nine species of closely‐related Mbuna bred throughout the year but all showed peaks of reproductive activity at times when food was most abundant. Most had a bimodal pattern of reproduction with a major peak in August to October, when plankton blooms were common, and another in February to March, when epilithic algae were plentiful. The smallest Mbuna species studied, Melanochromis joanjohnsonae, had a unimodal pattern, with high levels of reproductive activity extending for six to seven months of the year. Cyrtocara taeniolata, the only non‐Mbuna studied, had a highly synchronized unimodal pattern of reproduction. This species produced the smallest eggs, had the highest relative fecundity and was the only species that employed parental care of free‐swimming young. 1986 The Zoological Society of London
The evolution of cichlid fishes in Lake Malawi was studied using a small structural character, fine scale morphology. Because features of the scales are presumed to be selectively neutral and to be independent of a species' niche, similarities in scale structure may give an unbiased view of the relationships among extant species. The scale morphology of 20 endemic cichlid genera was examined. Several structures with possible value for taxonomic and evolutionary studies were identified, including six types of scale shape and three types of interradial denticle. A further character of use was the spiny area in the exposed part of the scale, which varied from non-existent to over 140° wide. Phylogenetic relationships revealed from scale characteristics were compared with those obtained from other methods which also utilize selectively neutral characters [mitochondrial DNA (mtDNA) and enzyme structure]. The degree of relatedness of taxa was then investigated in relation to the niche occupied. When the studied species were grouped in a dendrogram according to the similarity of their scales, grouping did not reflect the similarity of niches. Furthermore, electrophoretic and mtDNA studies of this species flock suggest that, although niche is a conservative character, fundamentally new niches have been invaded several times during the evolution of the studied species. The single basin structure of Lake Malawi offers no clear geographical barriers to facilitate allopatric speciation, but lake sediments indicate this seemingly homogeneous environment to have been historically heterogeneous. Geological sediment cores contain evidence of mass mortalities of fishes, and opportunities for niche switches may have resulted from released competition following local fish kills. The relaxation of competition following such events would have provided opportunities for niche switches, which may have driven some of the speciation in this group.
Synthesis of geological, historical, archaeological and geographical information is used to reconstruct detailed chronologies of the fluctuations of Lakes Malawi and Chilwa during the past two centuries and to produce less detailed, longer-term chronologies of these lakes. Fluctuations are compared with famine and drought records during historical times and rainfall data during modern times in order to understand their links with local and large-scale climatic conditions. This analysis underscores complexities in interpreting the historical and geological records of the lakes in terms of climate. It also points out the need to interpret the African lake record collectively, rather than focusing on individual lakes.
During the past 15 years, knowledge of intraspecific variation in haplochromine cichlids from Lake Victoria has greatly increased due to field and laboratory studies on ontogeny, phenotypic plasticity, polymorphism and sexual dimorphism. This paper reviews our current knowledge of intraspecific variation and evaluates its implications for species distinction. Continuous and prolonged ecological studies over the past two decades revealed that the number of haplochromine species in Lake Victoria is far higher than had been estimated prior to this research. As these species can be morphologically highly similar, overlooking intraspecific variation may obscure interspecific differences or even lead to erroneous conclusions on conspecificity.
This chapter explains the molecular systematics of a rapidly evolving species flock highlighting the mbuna cichlid fauna of Lake Malawi, an ecologically diverse assemblage of approximately 300 species. With the advent of molecular investigation and mitochondrial DNA (mtDNA) analysis in evolutionary studies, it was hoped that basic problems of cichlid phylogenetics would be resolved. Two major mtDNA lineages (α and β), differing by 1.5% sequence divergence, were identified within the mbuna. Some alternate molecular approaches need to be considered as mtDNA cannot provide sufficient information to resolve relationships within the mbuna. Variation at microsatellite loci is more promising. Such loci can exhibit extremely large numbers of alleles, differing in the number of a simple nucleotide repeat unit present. This chapter also includes tabular representation of morphological and ecological characteristics of three mbuna genera along with hypothetical and actual relationships between the three. It provides evidence that hypervariable microsatellite loci that contain phylogenetic information is potentially capable of resolving relationships within the mbuna.
The diagnosis of the genus Labidochromis is revised to include species with bicuspid outer teeth. Sixteen species, of which 13 are new, are described and illustrated and the validity of five others is discussed. The interrelationships between members of the genus and the relationship of the genus to other genera are discussed. No clearly defined sister group to the genus has been found either within or outside the Lake Malawi cichlid species flock. A key based on the coloration of known species is included.
Describes species richness of fishes in rivers and lakes of Africa with emphasis on Cichlidae. An explanation of the patterns which emerge is sought by exploring the speciation processes which may have contributed to the species diversity. The chapter explores processes and rates over large temporal scales. By examining the spatial distribution of fish assemblages and by comparing cichlids of large rivers and lakes, as well as those of tiny sinkholes and springs, it becomes possible to propose an hypothesis which may explain why the continent is so rich in species, why rivers have fewer species than lakes and why cichlid communities of sinkholes and spring have not differentiated as much as they might have, given the time-frame of their existence. Support from empirical evidence, however, is weak or non-existent, reflecting the fact that <50% of African freshwater fishes are described and that very little is known of the biology of the vast majority of species. -from Author
Mitochondrial DNA haplotype diversity and frequency distribution were examined within and among four narrowly endemic species and one cosmopolitan species of the rock-dwelling cichlid fish species flock (mbuna) of Lake Malawi in East Africa. The endemics, restricted to very small islands, appear to have originated less than 20,000 yr ago. Relative and absolute levels of genetic diversity were used to examine the possibility that these endemics arose through founder events, as has been suggested for the Hawaiian drosophiloids, to which the East African cichlids have been compared. Three principal results emerged from this study. First, the undescribed species Pseudotropheus zebra 'black dorsal' was found to be depauperate of mtDNA haplotype diversity relative to sister taxa, suggesting a severe population bottleneck during, or subsequent to, its recent origin. Second, significant differences in haplotype frequency existed among all five closely related species examined here. Geologic evidence and distributional limits indicate that this divergence in haplotype frequency occurred rapidly, consistent with population bottlenecks. Paradoxically, in three of four species examined there was no apparent reduction in genetic diversity, and two had haplotype diversity values that were high relative to other freshwater fishes. Third, it was found that replicate collections of single species at different sites within the same general locations, without obvious barriers to gene flow, also exhibited significant differences in haplotype frequency. Such apparent fine-scale genetic structuring, whether spatial or temporal, has substantial implications for estimates of effective population size and modeling of speciation processes.
Until a few years ago, Lake Victoria possessed a large species flock of haplochromine cichlids (250+ species). There is strong evidence that zooplanktivorous species from the Mwanza Gulf, which showed a large overlap in gross morphological characteristics, were ecologically segregated to a great extent. Species which segregated relatively little horizontally, did so vertically, and/or by different diet. The 2 species with the largest diet overlap segregated vertically. Species pairs segregated along at least one of the traditional niche axes: space, food and time. Vertical distributions of fish and food at a 14 m deep station correlated well by night. -from Authors
Mitochondrial DNA (mtDNA) restriction fragment length polymorphisms were assayed among 40 species of Lake Malawi haplochromines (Cichlidae) including representatives of ecologically divergent genera. Six distinctive mtDNA lineages were distinguished, two of which were major clades, represented by a large number of species. The other four lineages were each represented by a single species with a divergent mtDNA haplotype. One of the two major clades was composed of the shallow-water, rock-dwelling mbuna species, whereas the other included a diverse array of sand-dwelling and pelagic species. A number of taxa, found to be firmly embedded within the mbuna clade, are quite distinct in morphology and generally inhabit deeper, sediment-rich areas rather than the rocky habitats typical of other mbuna. The mbuna group is generally thought to be a monophyletic assemblage, but these results suggest that it is actually paraphyletic. In contrast to the high morphological diversity among Malawi haplochromine species, mtDNA sequence divergence was found to be remarkably low. This finding underscores the unprecedented rapidity of speciation and evolutionary plasticity in this fish species flock.
A number of facts and speculations relating to evolutionary phenomena within the basin of Lake Nyasa are put forward. It is shown that, in spite of its great size, Lake Nyasa does not provide either a great diversity of habitats or of different foods for the fishes that exhibit the most striking speciation of all the groups in the lake. Thus neither the existence of many habitats nor of a wide choice of foods can be called upon as means whereby this speciation could have been accomplished. The great size of the lake, enabling isolation by distance to become effective, is believed to have played an important part in permitting the evolution of numerous species. Various aspects of predation, supplementing evidence previously put forward, suggest that, contrary to the view of Worthington, the presence of numerous predators has facilitated and not impeded speciation. Although the cichlid fishes fill numerous niches, adaptive radiation has been restricted in that groups of related species, or even genera, frequently co-exist in the same habitat and often utilize similar foods. Examples of this type of radiation are given and comparison is made with the adaptive radiation more usually found elsewhere in the animal kingdom. Some new considerations, in addition to those already put forward by previous students of the lake, indicate that lake-level fluctuations have had a bearing on the speciation of the fishes. The evolution of plankton-feeding among the fishes of Lake Nyasa seems to have been invariably accompanied by the adoption of the shoaling habit. Examples of this, including an incipient case, are given. The suggestion is put forward that the shoaling habit is an example of "ecological neoteny." The fishes showing the most remarkable speciation in the lake are those of the family Cichlidae which, with only two known exceptions, neither endemic, are mouth-brooders. The habit of mouthbrooding is believed to have been important in the evolution of the many endemic species, and in permitting their co-existence in dense multispecific populations. Preliminary data suggest a distinct correlation between the size of the eggs produced, the number of young brooded by the female, and the habitat frequented by any given species of cichlid fish. Those species living in the most densely populated habitats produce few large eggs and rear small broods of young to a relatively large size, while species in less densely populated habitats produce larger numbers of relatively smaller young from smaller eggs. Relatively stable conditions prevailing over a long period of time have apparently provided an incentive to specialization to the fishes of Lake Nyasa such as is absent in most lakes which, geologically speaking, have but a short life span. This specialization had the inevitable consequence of restricting individual species to very definite habitats, thus rendering isolation of populations by even small barriers of unsuitable terrain an easy matter. Such conditions have been conducive to allopatric speciation.
Interspecific hybridization among haplochromine cichlids of the East African Great Lakes has been proposed as a mechanism for the evolution of new taxa in these highly speciose faunas; however, no obviously hybrid individuals have been collected, nor is it clear whether one could recognize hybrids if they did occur. Here we report on the morphology of experimentally produced F1 hybrids between Pseudotropheus zebra and Labeotropheus fuelleborni, two common Lake Malawi rock-dwelling haplochromine taxa (mbuna) that differ substantially in trophic morphology. We qualitatively describe the morphology of hybrids, and quantitatively analyze 13 descriptors of oral morphology using both univariate and multivariate procedures. Hybrids, although morphologically distinct, more closely resemble P. zebra than L. fuelleborni. Three individual oral jaw characters are intermediate in, and thus diagnostic of, hybrids; however, hybrids display unique patterns of expression for five characters. Discriminant function and canonical variates analysis clearly separate all three groups. The position of hybrids along canonical variate II suggests that hybrids are neither intermediate nor mosaic but rather display a novel multivariate phenotype. Our results suggest that (1) interspecific hybridization between these taxa does not occur under current conditions in Lake Malawi, (2) the genetic control of mbuna trophic morphology may involve a significant dominance component, and (3) hybrids (when produced) may lie along an ecomorphological trajectory distinct from that separating parents. As a consequence, we propose that phenotypic shifts in cichlid populations may be discontinuous and involve limited regulatory genetic change and that hybridization (if of historical importance) could result in the production of novel phenotypes with unique evolutionary potentials.
The fish communities of the rocky littoral zone of Lake Malawi contain a large number of ecologically similar cichlid species. It has been suggested that dietary niche segregation may play a role in the coexistence of these species, but previous studies have yielded ambiguous results. Stable isotope analysis was used to determine whether five sympatric species are segregated by diet. Significant differences were found between the mean isotopic signatures of the study species, but there was considerable interspecific overlap between three species from the same subgenus that were anatomically almost indistinguishable. The implication that this was due to substantial dietary similarity was supported by stomach content analysis. We propose that ecological segregation may not always be necessary to allow coexistence of Lake Malawi cichlids.
This chapter focuses on the cichlid fauna of Lake Tanganyika, the least studied of the African Great Lakes. It places particular emphasis on the faunas of the rocky shore habitats, and explores the great species diversity that may have arisen. The chapter describes the evolutionary scenarios within the lake and the biology of these fishes. Several of the more parsimonious explanations as to how the extant species diversity is maintained are considered, and examples of resource partitioning among coexisting species along a variety of resources axes, the most likely mechanism of coexistence, are given. It also illustrates several examples of the diversity of feeding and breeding habits seen both within groups and within species. Moreover, the cichlids of Lake Tanganyika offer splendid, perhaps unique, opportunities for studies of ecology, behavior and evolution, yet there is a paucity of quantitative information concerning the ecology and evolution of its species flocks, such that our present level of knowledge is insufficient on which to form comprehensive theories regarding factors structuring these communities.
Fatty acid composition in the muscle of eight endemic haplochromine cichlids and one tilapiine cichlid from Lake Malawi was studied by gas-liquid chromatography. The species studied represent a wide variety of niches: Algae combing, shell crushing, feeding on littoral and semipelagic zooplankton, detecting invertebrates hidden in the sediment using expanded lateral line canals, and fish predation in littoral and bathypelagic zones. The sampling was done during the early rainy season. The analysis of fatty acid composition suggests that despite the reported plasticity in feeding the niches of the species studied are established and stable. The proportion of eicosapentaenoic acid (20:5n-3) in relation to arachidonic acid (20:4n-6) illustrated the position of these species in the foodweb: equal proportions in algae feeders and clear 20:4n-6 dominance in species feeding on benthic prey. Although the number of replicates was small, discriminant analysis with 31 fatty acids separated the specimens into dense centers according to species. These results encourage the use of chemometric methods for studying ecological relationships among freshwater fauna and ongoing evolutionary processes.
A new species of the cichlid genus Pseudotropheus Regan (Teleostei: Cichlidae), from Lake Malawi is described. The new species is a member of the Pseudotropheus williamsi complex from Mbenji Island. Pseudotropheus williamsi is the type species of the genus Pseudotropheus, which is a polyphyletic grouping of several species of rock-dwelling cichlids from Lake Malawi. In addition to the P. williamsi complex, Pseudotropheus contains species belonging to the P. tropheops, P. elongatus, and Pseudotropheus aggressive complexes, as well as a group of miscellaneous forms such as Pseudotropheus fainzilberi. We predict that Pseudotropheus eventually will be restricted taxonomically to include only members of the P. williamsi complex, but because of the lack of phylogenetic data on many of the miscellaneous forms (e.g., P. fainzilberi) we are currently unable to diagnose Pseudotropheus as monophyletic.
Several papers have suggested that the Freshwater Cichlid Crenicara punctulata is capable of protogynous sex change. These studies provide behavioral data and descriptive details of external morphology but lack information about gonadal histology, which is essential for definitive evidence of sequential hermaphroditism. Therefore, this study was designed to determine whether C. punctulata is a sequential hermaphrodite. The present study included a behavioral experiment, an isolation/transformation experiment, as well as a detailed analysis of gonadal structure. The behavioral experiment established social hierarchies in four groups of juvenile female C. punctulata. The hypothesis that the dominant female in each group would be the only individual to develop male secondary sexual characteristics in that group was verified. The isolation experiment tested the hypothesis that female C. punctulata would change sex without the presence of conspecifics. After social isolation, females that were previously dominant among a group of females in a male harem developed male secondary sexual characteristics. Histological analysis revealed that these individuals possessed testes, whereas all dominant females examined possessed mature ovaries. The results from behavioral, isolation, and histological portions of this project strongly suggest that C. punctulata is a protogynous sequential hermaphrodite, at least in captivity.
Dominance relations in pairs of animals differ from those (between the same fishes) in groups of conspecifics. In groups M. auratus establishes and maintains a linear dominance hierarchy, of which the communicative structure is described. Number of aggressive interactions between 2 group members is determined by the rank number of the actor and the reactor. Most interactions occur between rank neighbours. 'Group factors' are looked for by analysing the clustering of all possible chase-interactions. Four categories of such clusterings are discussed: a preceding aggressive interaction can have an influence on high-ranked animals, the effect of such an influence is directed towards low-ranked animals. The stable hierarchy can be changed by successive circle fights. The highest-ranked group members always intervene in circle fights in order to stabilize the hierarchy, for their own benefit. This is another 'group factor'. An alpha animal has to spend all its energy in obtaining and maintaining its rank status. When it loses this position, it drops down the hierarchy. -from Author
Biogenic silica profiles in varved sediments from northern Lake Malawi (Nyasa), East Africa, span the past 700 yr and reflect past primary productivity in the overlying waters. On a centennial scale this has been influenced by lake level and a consequent shift in the location of high diatom productivity within the lake basin. Primary production was higher during the Little Ice Age, an arid period from about A.D. 1570 to 1850, when lake level was about 120 m lower than during the previous three centuries or the past 150 yr.
Three sympatrically occurring members of a cichlid fish species complex from Lake Malawi have previously been reported to show assortative mating in the field. Offspring from three experimental tanks each housing both sexes of all three members of this complex were screened at one to four microsatellite loci to determine paternity. Reproductive isolation was found to persist without exception under laboratory conditions, providing strong evidence for behavioural barriers to mating. Direct mate choice is suggested as the process preventing interbreeding. The results are interpreted with reference to the rapid and explosive evolution of the cichlid group.
Increased potential versatility in form and function of the feeding apparatus of cichlid fishes has led to a prodigious proliferation in the number of possible functional solutions to an increasing variety of biological problems. Optimal utilization of every conceivable trophic resource in lacustrine environments by just one fish family, the Cichlidae, has been achieved by eruptive evolutionary radiation within the characteristically cichlid body plan producing mechanisms which partition the diverse food resources with extraordinary efficiency therefore minimizing resource sharing. There is a direct relationship between the effectiveness of trophic resource exploitation and the functional integration of the cichlid body plan in which a minimum number of adaptive compromises are necessary to evolve optimal anatomical solutions by rapidly realizable changes
Anatomical data presented here reveal that cichlids possess a specific kind of mosaic in which the basic percoid jaw apparatus permits unparalleled optimal adaptations by simple morphogenetic changes while unique and dramatically diverse patterns of muscular coordination involving degrees of synchrony and extensive modulating capabilities of antagonistic muscle groups have been discovered electromyographically. At the same time the highly integrated pharyngeal jaw apparatus is sufficiently specialized providing complete freedom for the jaws to evolve into refined collecting devices.
The exceptional evolutionary success of lacustrine cichlids demonstrates how rare and very specific kinds of biologically versatile morphological mosaics represent the best preadaptations for the ancestors of major new taxa. Given identical ecological conditions and temporal factors, a group of organisms possessing such rare mosaics, in which optimal biological versatility is realizable by simple evolutionary mechanisms, will dominate newly formed environments to the detriment of taxa not so endowed.
The body colouration extending into ultraviolet wavelengths in three species of Lake Malaŵi rock‐dwelling cichlids, Metriaclima zebra, Metriaclima benetos and Metriaclima barlowi was quantified. All three species were ultraviolet reflective with interspecific differences in reflectivity. In addition, individuals were able to behaviourally mediate their reflectivity.
Females of the Lake Malawi cichlid Pseudotropheus lombardoi preferred males with one eggspot, the natural number, on their anal fin compared to males with two eggspots which had been artificially manipulated in number. Furthermore by manipulating the size of the eggspot. it was found that females preferred males with one large eggspot to males with one small eggspot. These results indicate that female preferences are responsible for the single eggspot in P. lombardoi and that this may be linked to species recognition as females of closely related species appear to exhibit different preferences for male eggspots.
The ability of three sympatric species ofPetrotolapia, from Monkey Bay, Lake Malawi, to penetrate deep water was tested using pressure chambers. The three species were found to differ in terms of the maximum pressure (= depth) to which each was able to equilibrate. Mean maximum equilibration pressures were for the form designated MOL 39.0 m, for MBB 35.5 m and for the form MOC 30.4 m. The rate of compensation to pressure changes was slower in MBB (2.59 m day-1) than in other two forms (MOL = 3.97 m day-1, MOC = 3.98 day-1). Natural depth distribution of all three forms, in particular MBB and MOC, is not determined by limits imposed by swin bladder physiology.
Synopsis Seven species of rock-frequenting cichlids, endemic to Lake Malawi, formed feeding-schools. Petrotilapia genalutea was the nuclear species comprising 92% of the school members (n = 2690 individuals from 50 schools). Fifty-eight per cent
of all schools encountered consisted only of P. genalutea. School size ranged from 10 to 300 members (x = 81 ± 74 SD, median = 62). Schooling behaviour was facultative. Ninety-seven
per cent of the feeding sites used by the schools occurred within the territories of highly aggressive, territorial species.
These sites support considerably greater standing crops of algae, the food of the schooling species, than undefended sites.
Individuals of schooling species were unable to gain access to the aggresively defended areas unless they joined schools.