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Ecological correlates of species differences in the Lake Tanganyika crab radiation
Abstract
The endemic crabs of Lake Tanganyika include a phenotypically diverse clade that exhibits recent divergence and low phylogenetic
species resolution. There are indications that ecological niche segregation has played a prominent role in the divergence
of this clade. We used habitat surveys, gut content analyses and stable isotope analyses to test the extent to which morphological
species are ecologically different. Our data show some interspecific segregation in depth, substrate type and mean stable
isotope signatures. At the same time, a considerable level of ecological niche overlap is evident among species of Platythelphusa that coexist in rocky littoral habitats. We consider these results in the framework of adaptive radiation theory, and we
discuss general ramifications for the maintenance of species diversity in Lake Tanganyika.
... Studies on the evolution of ancient lake organisms have continuously resulted in important insights into general patterns of speciation and radiation (e.g., Streelman andDanley 2003, Kocher 2004), including new insights from modern, integrative methods (e.g., Glor 2010, Naumenko et al. 2017. Like classic examples of adaptive radiations in fishes and mollusks, ancient lake species flocks of crustaceans are characterized by morphological and ecological adaptations: comprehensively studied examples of endemic adaptive radiations are decapods (shrimps and crabs) from the ancient lakes of Sulawesi (Malili lakes, Lake Poso; von Rintelen et al. 2012), decapods (mainly crabs, partly shrimps) from Lake Tanganyika (Marijnissen et al. 2008), and amphipods from Lake Baikal (Macdonald et al. 2005, Naumenko et al. 2017. ...
... Only the shrimp species flock in Lake Poso and the species flock of crabs in Lake Tanganyika colonized their respective lake only once: molecular studies revealed a common ancestry (monophyletic clade) of all shrimp species of the genus Caridina in Lake Poso (von Rintelen et al. 2012) and of the crab species of the genus Platythelphusa in Lake Tanganyika (Marijnissen et al. 2008). No molecular phylogeny is available yet for shrimps from Lake Tanganyika to test the number of lake invasions, but similar to Lake Baikal's amphipods, different endemic genera (Atyidae: Limnocaridina, Caridella, and Atyella) occur in the lake (Fryer 2006), and thus, more than one lake invasion is rather likely. ...
... In other words, they meet at least one of Schluter's ecological criteria as well, the phenotype-environment correlation. This kind of correlation has been well studied for the substratum preferences and subsequent adaptation of feeding appendages of the Sulawesian lake decapod radiations of shrimps (Atyidae; Fig. 11.5C) and crabs (Gecarcinidae) (von Rintelen et al. 2012) and the trophic morphology, habitat specificity, diet composition, and stable isotope analyses for the Lake Tanganyika crabs (Platythelphusidae) (Fig. 11.5D; Marijnissen et al. 2008). ...
Crustacea in standing waters are a diverse taxonomic assemblage with representatives in all available habitats from the benthic zone to the pelagial in larger water bodies. While most higher taxa are widespread and occasionally cosmopolitan, this is only partially true at the genus and species level. The crustacean fauna of geologically young lakes, or ponds, is characterized by widespread species that are not even necessarily restricted to lentic habitats. These species generally have good to excellent dispersal capabilities, especially those dwelling in ephemeral habitats. Small groups such as branchiopods and copepods dominate under these conditions among obligate still-water dwellers. In contrast, endemism and occasional striking adaptations are the hallmarks of crustacean species flocks, especially in the radiations of amphipods, decapods, and ostracods in the fewer than 10 ancient lakes worldwide. These radiations have arisen in situ through the diversification of unspecialized ancestors. All comparatively well-studied radiations for which molecular phylogenetic, taxonomic, and ecological data are available show particular adaptations of trophic morphology correlated to specific habitats. Prime examples are the species flocks of amphipods in Lake Baikal and of atyid shrimps in Lake Tanganyika and in two Indonesian lakes. These groups have most likely evolved through adaptive radiation. A major challenge for research on crustaceans in ancient lakes, and in standing waters generally outside Europe and North America, is the lack of basic data from species diversity to genetics for many, if not most, taxa. Getting a grip on species diversity, distributions, ecology, and, at a different level, genomics will be a research priority for coming decades.
... Studies on the evolution of ancient lake organisms have continuously resulted in important insights into general patterns of speciation and radiation (e.g., Streelman andDanley 2003, Kocher 2004), including new insights from modern, integrative methods (e.g., Glor 2010, Naumenko et al. 2017. Like classic examples of adaptive radiations in fishes and mollusks, ancient lake species flocks of crustaceans are characterized by morphological and ecological adaptations: comprehensively studied examples of endemic adaptive radiations are decapods (shrimps and crabs) from the ancient lakes of Sulawesi (Malili lakes, Lake Poso; von Rintelen et al. 2012), decapods (mainly crabs, partly shrimps) from Lake Tanganyika (Marijnissen et al. 2008), and amphipods from Lake Baikal (Macdonald et al. 2005, Naumenko et al. 2017. ...
... Only the shrimp species flock in Lake Poso and the species flock of crabs in Lake Tanganyika colonized their respective lake only once: molecular studies revealed a common ancestry (monophyletic clade) of all shrimp species of the genus Caridina in Lake Poso (von Rintelen et al. 2012) and of the crab species of the genus Platythelphusa in Lake Tanganyika (Marijnissen et al. 2008). No molecular phylogeny is available yet for shrimps from Lake Tanganyika to test the number of lake invasions, but similar to Lake Baikal's amphipods, different endemic genera (Atyidae: Limnocaridina, Caridella, and Atyella) occur in the lake (Fryer 2006), and thus, more than one lake invasion is rather likely. ...
... In other words, they meet at least one of Schluter's ecological criteria as well, the phenotype-environment correlation. This kind of correlation has been well studied for the substratum preferences and subsequent adaptation of feeding appendages of the Sulawesian lake decapod radiations of shrimps (Atyidae; Fig. 11.5C) and crabs (Gecarcinidae) (von Rintelen et al. 2012) and the trophic morphology, habitat specificity, diet composition, and stable isotope analyses for the Lake Tanganyika crabs (Platythelphusidae) (Fig. 11.5D; Marijnissen et al. 2008). ...
... Most studies focusing on the trophic ecology of species inhabiting East African Great Lakes to date have considered cichlids (Verheyen et al., 2003;Seehausen, 2006;Genner et al., 2007a, b;Day et al., 2008), whereas other taxa, including most invertebrates, remain largely unexplored (but see Berthold (1990) for divergence of trophic characters in the gastropod genus Lanistes from Lake Malawi). This is even more surprising given that species like freshwater crabs of the genus Platythelphusa (Potamonautidae; see ) have undergone an amazing radiation in Lake Tanganyika (Marijnissen et al., 2006;Reed & Cumberlidge, 2006), and, based on chelae morphology, trophic niche diversification was postulated as a driving force behind this diversification (West & Cohen, 1996;Marijnissen et al., 2008Marijnissen et al., , 2009). At the same time, shell morphology of snails from Lake Tanganyika is strikingly sophisticated-with thalassoid forms carrying rims, ridges, and spines (Huberndick, 1952;Glaubrecht, 2008)-which was hypothesized to reflect a co-evolutionary arms race with molluscivorous crabs (West & Cohen, 1994, 1996von Rintelen et al., 2004). ...
... For Lake Malawi, only one freshwater crab species of the family Potamonautidae is recorded: Potamonautes lirrangensis Rathbun, 1904(Rathbun, 1904Reed & Cumberlidge, 2006) or 'Malawi blue crab' (Dobson, 2004), a rather widespread species that also occurs in Lake Tanganyika. Freshwater crabs play a key role in linking various trophic levels within tropical aquatic ecosystems (Somers & Nel, 1998;Yeo et al., 2008;), but comparatively little information is available on their role in the food webs of the East African Lakes-the sole exception being the Platythelphusa species from Lake Tanganyika (Dobson, 2004;Marijnissen et al., 2008Marijnissen et al., , 2009. In Lake Malawi, the conchological diversity of mollusks in general is comparatively low (Michel, 1994;Van Damme & Gautier, 2012) and ornamented, thalassoid forms of Gastropoda are entirely missing. ...
... Freshwater crabs take a central position in aquatic food webs and are known to include a large spectrum of food items into their diet, such as algae, terrestrial plant matter, fine detritus, carrion and various invertebrates (Williams, 1961;Ng, 1988;Hill & O'Keeffe, 1992;Barbaresi & Gherardi, 1997;Scalici & Gibertini, 2007;Marijnissen et al., 2008Marijnissen et al., , 2009. Many species have an amphibious or semi-terrestrial mode of life, thus linking terrestrial and aquatic energy flows (Gherardi et al., 1988(Gherardi et al., , 1989). ...
Freshwater crabs play an important role for the diversification of shell morphologies in freshwater gastropods. For example, the radiation of the freshwater crab genus Platythelphusa in Lake Tanganyika is thought to have driven shell diversification of the lake’s snail fauna, promoting the evolution of thalassoid shells. No comparable thalassoid snails are known from Lake Malawi. Accordingly, it was hypothesized that the lake’s only freshwater crab, Potamonautes lirrangensis, is not a snail predator. We tested this hypothesis using feeding experiments with specimens caught in the southern part of Lake Malawi. Individual crabs were held in experimental containers offshore and were presented with various food items overnight, after which ingestion frequency was recorded. Potamonautes lirrangensis can be characterized as a scavenger that is opportunistically carnivorous. A preference for fish and snail flesh could be observed, indicating a bias toward carnivory. We observed occasional cracking of the shell in different snail species, with frequent ingestion of artificially crushed specimens, suggesting that crabs do attempt to feed on snails. However, the investigated Lake Malawi gastropods appear to be partly protected against crab predation through thick-walled and low spired shells (especially Lanistes and Bellamya), obviating the evolution of thalassoid shells carrying rims, ridges, or spines
... Most studies focusing on the trophic ecology of species inhabiting East African Great Lakes to date have considered cichlids (Verheyen et al., 2003;Seehausen, 2006;Genner et al., 2007a, b;Day et al., 2008), whereas other taxa, including most invertebrates, remain largely unexplored (but see Berthold (1990) for divergence of trophic characters in the gastropod genus Lanistes from Lake Malawi). This is even more surprising given that species like freshwater crabs of the genus Platythelphusa (Potamonautidae; see ) have undergone an amazing radiation in Lake Tanganyika (Marijnissen et al., 2006;Reed & Cumberlidge, 2006), and, based on chelae morphology, trophic niche diversification was postulated as a driving force behind this diversification (West & Cohen, 1996;Marijnissen et al., 2008Marijnissen et al., , 2009). At the same time, shell morphology of snails from Lake Tanganyika is strikingly sophisticated-with thalassoid forms carrying rims, ridges, and spines (Huberndick, 1952;Glaubrecht, 2008)-which was hypothesized to reflect a co-evolutionary arms race with molluscivorous crabs (West & Cohen, 1994, 1996von Rintelen et al., 2004). ...
... For Lake Malawi, only one freshwater crab species of the family Potamonautidae is recorded: Potamonautes lirrangensis Rathbun, 1904(Rathbun, 1904Reed & Cumberlidge, 2006) or 'Malawi blue crab' (Dobson, 2004), a rather widespread species that also occurs in Lake Tanganyika. Freshwater crabs play a key role in linking various trophic levels within tropical aquatic ecosystems (Somers & Nel, 1998;Yeo et al., 2008;), but comparatively little information is available on their role in the food webs of the East African Lakes-the sole exception being the Platythelphusa species from Lake Tanganyika (Dobson, 2004;Marijnissen et al., 2008Marijnissen et al., , 2009. In Lake Malawi, the conchological diversity of mollusks in general is comparatively low (Michel, 1994;Van Damme & Gautier, 2012) and ornamented, thalassoid forms of Gastropoda are entirely missing. ...
... Freshwater crabs take a central position in aquatic food webs and are known to include a large spectrum of food items into their diet, such as algae, terrestrial plant matter, fine detritus, carrion and various invertebrates (Williams, 1961;Ng, 1988;Hill & O'Keeffe, 1992;Barbaresi & Gherardi, 1997;Scalici & Gibertini, 2007;Marijnissen et al., 2008Marijnissen et al., , 2009. Many species have an amphibious or semi-terrestrial mode of life, thus linking terrestrial and aquatic energy flows (Gherardi et al., 1988(Gherardi et al., , 1989). ...
Freshwater crabs play an important role for the diversification of shell morphologies in freshwater gastropods. For example, the radiation of the freshwater crab genus Platythelphusa in Lake Tanganyika is thought to have driven shell diversification of the lake’s snail fauna, promoting the evolution of thalassoid shells. No comparable thalassoid snails are known from Lake Malawi. Accordingly, it was hypothesized that the lake’s only freshwater crab, Potamonautes lirrangensis, is not a snail predator. We tested this hypothesis using feeding experiments with specimens caught in the southern part of Lake Malawi. Individual crabs were held in experimental containers offshore and were presented with various food items overnight, after which ingestion frequency was recorded. Potamonautes lirrangensis can be characterized as a scavenger that is opportunistically carnivorous. A preference for fish and snail flesh could be observed, indicating a bias toward carnivory. We observed occasional cracking of the shell in different snail species, with frequent ingestion of artificially crushed specimens, suggesting that crabs do attempt to feed on snails. However, the investigated Lake Malawi gastropods appear to be partly protected against crab predation through thick-walled and low-spired shells (especially Lanistes and Bellamya), obviating the evolution of thalassoid shells carrying rims, ridges, or spines.
... Convincing arguments that abiotic changes did have a severe impact on Lake Tanganyika's fauna have recently been found by molecular phylogenetic research, e.g., on molluscivorous plathytelphusid crabs, limnochromine cichlids, Synodontis catfish and mastacembelid eels. The studies indicate that the radiations in these groups are geologically recent events (late Pliocene-early Pleistocene; Cumberlidge et al., 1999;Marijnissen et al., 2006Marijnissen et al., , 2008Duftner et al., 2005;Day and Wilkinson, 2006;Brown et al., 2010). Since speaking in geological terms, the specialized molluscivorous crabs evolved only recently, the onset of the radiation in the thalassoid Lavigeria and others, considered to result from an armsrace between crabs and their prey (West et al., 1992), must also date from late Pliocene or early Pleistocene times at the earliest. ...
... The quite impressive Holocene radiation of Lavigeria in Lake Rukwa (Fig. 3), when this lake was joined with Lake Tanganyika via the Karema Gap (Cox, 1939;Cohen et al., 2010) may indicate that the evolutionary divergence process in Lavigeria is still an ongoing process. On-going divergence is also suggested for the plathytelphusid crabs (Marijnissen et al., 2008). ...
In terminal Pliocene–early Pleistocene times, part of the Malawi Basin was occupied by paleo-lake Chiwondo. Molluscan biostratigraphy situates this freshwater lake either in the East African wet phase between 2.7–2.4 Ma or that of 2.0–1.8 Ma. In-lake divergent evolution remained restricted to a few molluscan taxa and was very modest. The lacustrine Chiwondo fauna went extinct at the beginning of the Pleistocene. The modern Lake Malawi malacofauna is depauperate and descends from ubiquistic southeast African taxa and some Malawi basin endemics that invaded the present lake after the Late Pleistocene mega-droughts. The Pleistocene aridity crises caused dramatic changes, affecting the malacofauna of all East African lakes. All lacustrine endemic faunas that had evolved in the Pliocene rift lakes, such as paleo-lake Chiwondo, became extinct. In Lake Tanganyika, the freshwater ecosystem did not crash as in other lakes, but the environmental changes were sufficiently important to trigger a vast radiation. All African endemic lacustrine molluscan clades that are the result of in-lake divergence are hence geologically young, including the vast Lavigeria clade in Lake Tanganyika (ca. 43 species).
... Cichlids and gastropods aside, these radiations are on a much smaller scale (10-15 species) and at a lower taxonomic rank. Until recently (West & Michel, 2000;Wilson et al., 2004;Day & Wilkinson, 2006;Koblemü ller et al., 2006;Marijnissen et al., 2006Marijnissen et al., , 2008 the evolutionary significance of such faunas has been overlooked; yet, they provide important comparative systems that may help us to better understand processes responsible for clade diversification and generalities across diverse taxa. ...
... lamprologine cichlids, Day et al., 2007) and Platythelphusa crab radiations (Marijnissen et al., 2006), they are instead largely cryptic, and display no sexual dimorphism. Ecological niche segregation has been demonstrated to play an important role in the divergence of crabs (Marijnissen et al., 2008) and cichlids (e.g. Hori, 1991), but has not yet been investigated in Synodontis. ...
Synodontis catfish are a species-rich, tropical pan-African genus that predominately occur in fluviatile environments, but which also form a small radiation within Lake Tanganyika (LT). Here we estimate Synodontis relationships, based on mitochondrial and nuclear DNA, greatly expanding previous sampling. Data were analysed using different methods of phylogenetic inference: Bayesian (also testing compositional heterogeneity), likelihood and parsimony, in order to investigate biogeographic history and the extent of intralacustrine speciation within this group. Bayesian-relaxed clock analyses were used to estimate timings of radiations. Our analyses reveal a single origin of the LT flock with the inclusion of the nonendemic S. victoriae, and that these taxa evolved relatively recently (5.5 Ma), considerably later than the formation of LT (9-12 Ma). Two internal endemic clades diversified at a similar time (2-2.5 Ma), corresponding to a period of climate change, when lake levels dropped. We find evidence for a further species flock, composed of riverine southern African taxa, the diversification of which is very rapid, 0.8 Ma (95% HPD: 0.4-1.5) and infer a similar scenario for the diversification of this flock to southern African serrachromine cichlids in that they radiated in the now extinct lake Makgadikgadi. We also reveal that the biogeographic history of Synodontis catfish is more complex than previously thought, with nonmonophyletic geographic species groupings.
... The shell morphology and structure, in general, play an important role to reduce the predation pressure, as observed for P. acuta against the malacophagous leech (Wilken and Appleton 1991). Further, the thick shells and spikes resist the predation from shell-crushers (Marijnissen et al. 2008) and the presence of operculum resist the invasion of shell-invader predators (Kelly and Cory 1987). In the Indian context, the shell-invader predators in freshwater habitats, mainly composed of leeches and hemipteran bugs Raut 2002a, 2002b), often fail to make successful attack on the native operculate snails (Aditya and Raut 2005). ...
The carnivorous snail Clea (Anentome) helena (von dem Busch, 1847) (Gastropoda: Nassariidae), commonly called as the “assassin snail” is sold worldwide including India for aesthetics and the ability to kill pest snails in aquaria. Assuming invasion as a fair possibility, the predation potential of C. helena on seven native freshwater snails was assessed. The exotic predator consumed all the native snail species provided in the experiment and prey consumption varied with the prey species identity, the prey density and the prey size class. Future colonization and establishment of C. helena in Indian freshwater ecosystems may reduce the abundance of the native gastropod snails, in absence of suitable intervention.
... An ecological niche of a species is an abstract mapping of population parameters onto multidimensional environmental space, the axes of which are abiotic and biotic factors that influence birth and death rates (Holt 2009). Speciation of freshwater crabs can be linked with niche segregation and diversification (Marijnissen et al. 2008), but the present changing environments and habitat loss can also contribute to niche shifts (Cumberlidge et al. 2009). ...
Isolapotamon mindanaoense (Rathbun 1904) and Sundathelphusa miguelito Mendoza and Sy 2017 have narrow biogeographical distribution and are both regarded as endemic to Mindanao island. They are common and publicly consumed freshwater or semi-terrestrial crabs inhabiting vicinities near the waterfalls of Lake Sebu Municipality, South Cotabato in Mindanao, but both species are scarcely investigated. This study aimed to examine the body size, microhabitat and the feeding ecology of these freshwater crab species. Sex and carapace width and length of individuals were determined from specimens collected by hand at three waterfall sampling sites. Feeding and feeding niche overlap were respectively analyzed using the index of relative importance (IRI) of prey items from individual crab stomachs and the Schoener's R o index. Food items ingested include fish fragments, insect body parts, fragments of aquatic vascular plants, freshwater algae, sand grains and amorphous materials, and these items were similar between species. However, the larger I. mindanaoense appeared to ingest more fish fragments and other animal prey items compared to S. miguelito which ingested more amorphous materials that are derived from benthic plants. However, the R o value of 93% was high, suggesting very similar diet. The two species further partition niches, with S. miguelito being smaller in size and inhabiting sand and gravel substrate, while the larger I. mindanaoense inhabit areas with big boulders. Hence, the crabs can be categorized as omnivorous and detrivorous, and exhibit feeding and habitat niche partitioning that alleviate possible resource competition between the two species.
... The best known example certainly is the amphipod radiation in Lake Baikal (Macdonald et al. 2005). Among the few cases of ancient lake radiations in decapod crustaceans are the endemic species flocks of freshwater crabs and shrimps in Lake Tanganyika (Fryer 2006;Marijnissen et al. 2008) and of crabs and shrimps in the two ancient lake systems of the Indonesian island Sulawesi, the former Celebes (Schubart & Ng 2008;von Rintelen & Cai 2009). ...
Freshwater shrimps of the genus Caridina are the most speciose group within the family Atyidae. This diversity can be witnessed in two ancient lake systems of the Indonesian island Sulawesi, where 21 currently described species, reflect the largest radiations of freshwater shrimps known worldwide. Both lake systems provide similar environmental conditions with locally heterogeneous habitats: Lake Poso is a single lake with less pronounced geographic structure than the Malili lake system with five lakes forming part of the same drainage system. The spatial subdivision in the Malili lakes and the higher number of species compared to Lake Poso (15 vs. 6) renders this system special interest for the study of geographic differentiation. Using mitochondrial DNA data, the phylogeographic patterns of the majority of the lacustrine species in the radiations are assessed. Both lake systems have been sampled comprehensively over several years, i.e. 137 localities altogether. A molecular phylogeny based on two standard genes (16S and COI) was reconstructed. A mismatch between molecules and morphology hints towards cases of introgression or incomplete lineage sorting in some species. To analyse geographic differentiation , geographic data for each species was mapped onto the phylogeny. In addition, haplotype networks were constructed to assess intralacustrine geographic patterns. In general, the molecular phylogeny revealed that all species, with one exception, are endemic to the ancient lakes, always showing local endemism within one system or even single lakes. Species from the Malili lakes revealed more geographic differentiation than species from the solitary Lake Poso. In several species from the Malili lakes, geographically separated populations form distinct subclades, suggesting limited gene flow between these populations. In other cases, allopatrically occurring populations within species were found in separate clades that were not even sister groups to each other in the overall phylogeny. This suggests not only the existence of cryptic species but also of unrecorded endemism.
... An in situ rapid radiation of Platythelphusa in Lake Tanganyika is supported by the short internal branches and the low statistical support among species. There is some evidence to suggest that Platythelpusa species are ecologically differentiated in habitat and diet, allowing them to occur sympatrically (Marijnissen et al., 2008). A second invasion of Lake Tanganyika is represented by a single species of Potamonautes All Liberonautes species are restricted to West Africa; the westernmost limit being Senegal and the eastern limit Ghana (Cumberlidge, 1999;Cumberlidge & Huguet, 2003). ...
Evolutionary‐based measures of biodiversity play an increasingly important role in theoretical conservation biology, complementing more traditional methods such as patterns of species richness and endemicity. To date, very few studies have used evolutionary data to assess patterns of biodiversity in the Afrotropical region, particularly for freshwater invertebrate taxa. In the present study, the monophyletic Afrotropical freshwater crab family Potamonautidae was used to investigate how phylogenetic data can be combined with other metrics to help develop conservation plans for regional and species‐based conservation efforts. The Afrotropical freshwater crabs make an exceptional group to demonstrate the utility of a phylogeny‐based approach to conservation, as there have recently been a number of phylogenetic studies on this family, the IUCN Red List conservation status is available for almost every species, and accurate distributional range data are available for all species. The conservation priority of this fauna is assessed in relation to the Afrotropical freshwater ecoregions using three traditional measures of biodiversity and two phylogenetic diversity metrics. The results of Evolutionarily Distinct Globally Endangered and Heightened Evolutionary Distinctiveness and Globally Endangered analyses identify both the freshwater crab species and the areas of high conservation priority in the Afrotropical region.
... This is surprising, because African freshwater crabs likely face ample ecological opportunities for adaptive diversification in ancient lakes because they can occupy a range of trophic niches such as shredding (Hill & O'Keeffe, 1992;Dobson et al., 2002;Masese et al., 2014) and predation (West & Cohen, 1994;Weigand et al., 2014). In Lake Tanganyika, primary freshwater crabs of the family Potamonautidae have formed a small endemic species flock comprising nine phylogenetically closely related, but morphologically and ecologically differentiated Platythelphusa species (Cumberlidge et al. 1999;Marijnissen et al., 2004Marijnissen et al., , 2006Marijnissen et al., , 2008Marijnissen et al., , 2009). Nevertheless, their species diversity lags far behind the c. 250 cichlid species in this lake (Turner et al., 2001). ...
Lake Malawi is famous for the rapid speciation of cichlid fishes, but the potential diversification of its invertebrate fauna is poorly studied. Using two mitochondrial DNA sequence markers (partial ND1 and Cyt b genes), we investigated the population genetic structure of the only known species of freshwater crab inhabiting Lake Malawi (Potamonautes lirrangensis (Rathbun, 1904)). We detected little overall genetic differentiation among different sampling sites (pairwise ΦST-values = 0.00–0.13). Genetic differentiation between sampling sites was better explained by linear distances than by shoreline distances, suggesting that ‘sweepstake dispersal’ between western and eastern shores occurs. Moreover, several population genetic parameters (Tajima’s D, Fu’s FS, Fay and Wu’s H and mismatch distribution analysis) suggest a recent population expansion, and Bayesian skyline plot analysis confirmed a sudden increase of the effective population size between 70 and 30 ka. Genetic diversity decreased towards the southern, shallower part of the lake, suggesting a more recent colonization of the southern shores. This finding is in line with hypotheses on Lake Malawi’s paleogeography suggesting that the lake largely desiccated during Pleistocene East African megadroughts and re-expanded southwards only recently after ~ 70 ka.
... 15 The quite impressive Holocene radiation of Lavigeria in Lake Rukwa, when this lake was joined with Lake Tanganyika (Cox, 1939;Cohen et al., 2010) may indicate that the evolutionary divergence process in Lavigeria is still an ongoing process. On-going divergence is also suggested for the plathytelphusid crabs (Marijnissen et al., 2008). ...
In Terminal Pliocene-Early Pleistocene times, part of the Malawi Basin
was occupied by palaeo-lake Chiwondo. Molluscan biostratigraphy situates
this freshwater lake either in the East African wet phase between
2.7-2.4 Ma or that of 2.0-1.8 Ma. In-lake divergent evolution remained
restricted to a few molluscan taxa and was very modest. The lacustrine
Chiwondo fauna went extinct at the beginning of the Pleistocene. The
Modern Lake Malawi malacofauna is poor and descends from ubiquistic
South-East African taxa and some Malawi Basin endemics that invaded the
present lake after the Late Pleistocene mega-droughts. The Pleistocene
aridity crises caused dramatic changes, affecting the malacofauna of all
East African lakes. All lacustrine endemic faunas that had evolved in
the Pliocene rift lakes, such as palaeo-lake Chiwondo, became extinct.
In Lake Tanganyika, the freshwater ecosystem did not crash as in other
lakes, but the environmental changes were sufficiently important to
trigger a vast radiation. All African endemic lacustrine molluscan
clades that are the result of in-lake divergence are hence geologically
young, including the vast Lavigeria clade in Lake Tanganyika (ca. 43
species).
... P. reticulata and P. maculata in Singapore inhabit peat swamp and lowland forest streams, respectively; Ng, 1990), or occupy otherwise different ecological niches (e.g. the sympatric species in the ancient lakes of Sulawesi, see Schubart et al., 2008). Thus, ecological speciation might be an important driver of local diversification, as shown for potamonautid freshwater crabs in Lake Tanganyika (Marijnissen et al., 2008). Unfortunately, detailed ecological data for many sympatric species (e.g. on Bali and in south Sumatra) are still lacking. ...
AIM: We investigate the biogeographical history of the species-rich Sundaic freshwater crab genus Parathelphusa (family Gecarcinucidae). In particular, we ask to what extent eustatic sea-level fluctuations influenced diversification and species distribution. We test the prediction that sea-level fluctuations in the course of the Pleistocene glaciations increased speciation rates.
Location: Malay Peninsula, Greater Sunda Islands (Borneo, Java, Sumatra, Sulawesi), Bali and the Philippines (Palawan, Mindoro).
METHODS: Phylogenetic inference calculations were based on partial mitochondrial cytochrome c oxide subunit I (COX1), 16S ribosomal RNA and nuclear histone subunit 3 (H3) genes using maximum likelihood, maximum parsimony and Bayesian approaches. Divergence time estimation was performed with BEAST based on external substitution rates. Biogeographical analyses were conducted with a parametric likelihood method (LAGRANGE) and a bayesian method (BAYESTRAITS). Lineage diversification was studied with a lineage-through-time plot, and a maximum likelihood approach as implemented in the R package LASER.
RESULTS: We propose a Late Miocene age for the most recent common ancestor of Parathelphusa, with an ancestral range covering Borneo and the adjacent part of Sundaland. The evolution of six lineages pre-dates the Pliocene, five of them occurring on Borneo. Subsequent dispersal during the Miocene and Pliocene extended the range of Parathelphusa to the Philippines, Sulawesi, the Malay Peninsula and Sumatra, and, during the Late Pliocene and Pleistocene, to Java. Pleistocene divergence occurred between species from the Malay Peninsula and Sumatra, Java and Sumatra, and Java and Borneo.
MAIN CONCLUSIONS: Although low sea levels during the Pleistocene in all probability facilitated the dispersal of freshwater crabs among the Greater Sunda islands (excluding Sulawesi, which is not part of the Sunda Shelf), there is no complete Pleistocene geographical admixture of species, and pre-Pleistocene biogeographical patterns were retained. Furthermore, Pleistocene vicariance did not lead to an increased diversification rate in Parathelphusa. Instead, single colonization events out of Borneo during the Neogene, followed by species radiation (e.g., on Palawan and Sulawesi), contributed substantially to species diversity in Parathelphusa. This involved the crossing of marine barriers such as the Wallace Line.
... Today, such trees are available for most iconic adaptive radiations as well as a range of lesser-known examples. Adaptive radiations occurring in Lake Tanganyika, one of Africa's large Rift Lakes, are emblematic of this progress, with phylogenies now available not only for this lake's famous cichlid fauna [reviewed by Koblmüller et al. (2008)] but also for its lesser-known gastropods (Strong & Glaubrecht 2008), catfish (Day et al. 2009), crabs (Marijnissen et al. 2008), and prawns (Fryer 2006). ...
Adaptive radiation is a response to natural selection and ecological opportunity involving diversification of species and associated adaptations. Although evolutionary biologists have long speculated that adaptive radiation is responsible for most of life's diversity, persistent confusion and disagreement over some of its most fundamental questions have prevented it from assuming a central role in explaining the evolution of biological diversity. Today, answers to many of these questions are emerging from a new wave of integrative research that combines phylogenetic trees with a variety of other data and perspectives. In this review, I discuss how modern phylogenetic analyses are central to (a) defining and diagnosing adaptive radiation, (b)identifying the factors underlying the occurrence and scope of adaptive radiation, (c)diagnosing predictable patterns of ecological diversification during adaptive radiation, and (d) reconstructing the history of adaptive radiations.
... Cichlid utilization of empty Neothauma shells is well documented, but other fish including Auchenoglanis occidentalis (Valenciennes), a bagrid catfish, appear to utilize shells in nest-building activities as well ( Ochi et al., 2001). Certain crab species, including Platythelphusa maculata Cunnington, also appear to be restricted to Neothauma-rich substrates (Marijnissen et al., 2008). The small, rounded bodies of P. maculata and their marked substrate preference suggest a potential evolutionary adaptation reliant on the presence of Neothauma shell beds. ...
Lake Tanganyika, the world’s largest tropical rift lake, is unique among its
counterparts in East Africa for the remarkable diversity of mollusk-rich
sediments in its littoral zone. Molluscan shell beds are, however, a common
feature of ancient lacustrine rift deposits and thus a better understanding of
their spatial and temporal development is important. Targeted surveys
across the littoral region of the Kigoma Basin reveal three surficial shellrich
facies that differ widely in depositional style and geometry. A unifying
characteristic of these deposits is the volume of shells of Neothauma
tanganyicense, a large, viviparous gastropod endemic to the lake.
Reservoir-corrected radiocarbon dating indicates that Neothauma deposits
in these surficial sediments are time averaged over at least the last 1600
calendar years BP. Preservation of fossil Neothauma shells in the littoral
zone depends on both environmental conditions and on post-mortem shell
modifications. Interaction between shells and mobile siliciclastic grains,
facilitated by wave action and storms, represents a particularly destructive
taphonomic process in the study area. Rank scoring of damage to
Neothauma suggests that stromatolitic encrustations or early calcite
coatings may help mitigate shell destruction caused by hydraulic
fragmentation and abrasion. Persistence of Neothauma in littoral beds
has important implications for the structuring of specialized communities of
shallow-water benthos, as well as for improving analog models for
hydrocarbon reservoirs in lacustrine carbonates.
... Crabs can also be eVective indicators of pollution and general aquatic ecosystem health (Schuwerack et al. 2001; Bowen and Depledge 2006, and references therein). Based on their benthic habitat 1 C use (Marijnissen et al. 2008), we expect that the endemic crabs of Lake Tanganyika are highly sensitive to sedimentation. Shifts in crab abundance or diversity could have wideranging consequences through their eVects on prey populations. ...
Sedimentation resulting from riparian deforestation has a wide range of detrimental effects on aquatic biodiversity, but predicting
the full consequences of such disturbances requires an understanding of the ecosystem’s key functional components. We investigated
the ecology and response to sedimentation of the diverse, endemic freshwater crabs of Lake Tanganyika, which may occupy important
positions in littoral foodwebs. Our surveys revealed crab distribution patterns to be patchy, and that crabs can be locally
abundant (0–28 individuals m−2). Crab densities decreased with depth and the dry mass of crab assemblages ranged from 0.0 to 117.7gm−2. Comparisons among sites revealed significant effects of sedimentation on crab assemblage evenness, but provided no evidence
that sedimentation has altered densities, incidence or species richness. The resilience of crabs to sedimentation might be
related to their intraspecific dietary breadth. Stable isotope data (δ13C and δ15N) from crabs and their potential food resources indicated differences in trophic roles among endemic crab species. Overall,
crabs occupy higher trophic positions than most other invertebrates, and they draw upon both benthic and planktonic energy
pathways. The high biomass and top-predator status of some crab species suggests the potential for cascading effects on organisms
lower in the food web.
Geologic origins and climatic factors have affected the degree of isolation and ages of habitats so that new species evolved in many different types of inland waters. Today these rivers, lakes and wetlands support a disproportionate number of all the described species on earth relative to the size of surface-water habitats. This concentration of diversity resulted in part because of many periods of isolation and changes in hydrology. Endemic species evolved and adapted to distinct habitats in response to specific environmental conditions and biotic interactions. However, concentrations of endemic species increase the risk of extinctions so that the loss of inland aquatic species is accelerating at faster rates than in marine or terrestrial ecosystems. Some of the most diverse groups of aquatic organisms illustrate general patterns of biodiversity that influence food webs and ecosystem processes. Biodiversity indices are also used to monitor water quality to inform management. Despite increased research over the last several decades, many species remain to be discovered and most life histories and ecological relationships are incompletely known.
The endemic gastropods of Lake Tanganyika have often been characterized as being convergent with marine species, but this intuition has not been evaluated. Most of the Tanganyikan species belong to the superfamily Cerithioidea, a clade that also contains numerous marine species. Using a trait-based approach, I show that only 12 derived shell and opercular traits in Cerithioidea (41%) evolved independently in marine and Tanganyikan species; 16 derived traits (54%) are unique to marine representatives, and only one is unique to Lake Tanganyika. The high diversity of morphology observed in both marine and Tanganyikan cerithioideans indicates that the ancestral states and early clade history did not greatly constrain subsequent phenotypic occupation of morphospace and that this diversification occurred both with and without interference from other diversifying gastropod clades.
This chapter discusses the specifics of meromixis in lakes at low latitudes. The lack of strong seasonality, year-round high temperatures, and high irradiance levels create conditions that are rarely manifested in temperate lakes. For example, while in temperate lakes the absence of vertical mixing (meromixis) requires a strong salinity gradient to stabilize the water column against thermal convection, deep tropical lakes may remain stable without it, with deep waters ventilated by slow basin-scale circulation. Similarly to temperate meromictic lakes, tropical lakes accumulate nutrients in their anoxic monimolimnia, but the role of those deep nutrient sources for primary production becomes significantly greater. Primary production is higher on a given nutrient base than in temperate lakes. Evaporation, rates of vertical water exchange, and wind patterns become important factors for the stability of stratification and nutrient fluxes, while responses to climate change may be variable and complicated. Focusing primarily on deep (large) tropical lakes, we first review the general features of meromixis in such environments, including physical, chemical, biological, and microbiological aspects. We then discuss more detailed examples from the East African lakes Tanganyika and Malawi and the Indonesian Lake Matano, followed by a brief mentioning of several other tropical meromictic lakes.
Phylogenetic reconstruction, divergence time estimations and ancestral range estimation were undertaken for 66% of the Afrotropical freshwater crab fauna (Potamonautidae) based on four partial DNA loci (12S rRNA, 16S rRNA, cytochrome oxidase one (COI) and the histone 3 gene). The present study represents the most comprehensive taxonomic sampling of any freshwater crab family globally, and explores the impact of paleodrainage interconnectivity on cladogenesis among freshwater crabs. Phylogenetic analyses of the total evidence data using maximum likelihood, maximum parsimony, and Bayesian inference produced a robust statistically well-supported multi-locus topology that reaffirmed the monophyly of the Afrotropical freshwater crab fauna. The estimated divergence times suggest that the Afrotropical Potamonautidae diverged during the Eocene. Cladogenesis within and among several genera occurred predominantly during the Miocene, which was associated with major tectonic and climatic ameliorations throughout the region. Paleodrainage connectivity was observed with specimens from the Nilo-Sudan and East African coast proving to be sister to specimens from the Upper Guinea Forests in West Africa. In addition, we observed strong sister taxon affinity between specimens from East Africa and the Congo basin, including specimens from Lake Tanganyika, while the southern African fauna was retrieved as sister to the Angolan taxa. Within the East African clade we observed two independent transoceanic dispersal events, one to the Seychelles Archipelago and a second to Madagascar, while we observe a single transoceanic dispersal event from West Africa to São Tomé. The ancestral area estimation suggested a West African / East African ancestral range for the family with multiple dispersal events between southern Africa and East Africa, and between East Africa and Central Africa. The taxonomic implications of our results are discussed in light of the widespread paraphyly evident among a number of genera.
© The Author(s) 2015. Published by Oxford University Press, on behalf of the Society of Systematic Biologists. All rights reserved. For Permissions, please email: journals.permissions@oup.com.
Ancient lakes are excellent laboratories for evolutionary research, where species can be studied in the cradle where they originated. In this article, we investigate two endemic ostracod species flocks from the two oldest lakes in the world, Lake Baikal (LB) (ca. 28 myr) and Lake Tanganyika (LT) (ca. 12 myr), with DNA sequence data. Nuclear ITS1 failed to resolve the phylogeny of both flocks. Whilst most phylogenetic relationships of the Tanganyika flock are resolved with mitochondrial COI, the Baikalian tree contains multifurications of up to seven different clades. The Tanganyikan Cyprideis flock shows higher genetic variability, which matches its higher morphological variability. A significant deviation from a constant divergence rate through time indicates that the Cytherissa flock most likely experienced explosive speciation events during its earlier history. Comparative analyses of substitution rates furthermore revealed that they are not clock-wise for COI. Ancestral Cytherissa probably radiated in LB 5–8 myr ago, around the time when the cold, oxygenated abyss was formed in LB. The Tanganyikan Cyprideis flock is almost twice as old as the Baikalian Cytherissa flock, and possibly older than LT itself, ca. 15 myr. The Cyprideis flock has survived drastic lake level changes and resulting salinity crises during its entire history.
Explanations for the coexistence of many closely related species in inland waters continue to be generated more than 50years
after Hutchinson’s question: why are there so many kinds of animals? This review focuses on the hypothesis that high species
diversity of freshwater gastropods results, in part, from predators maintaining biodiversity across a range of deep- and shallow-water
habitats. Invertebrate predators, such as aquatic insects, and leeches consume soft tissue of pulmonate snails by penetrating
shells of various shapes and sizes. Crayfish and large prawns chip around the shell aperture to enter thick shells and crush
small shells with their mandibles. Crabs use their strong chelae to crush thin and thick shells. Fishes with pharyngeal teeth
are major shell-breaking predators that combine with other vertebrate predators such as turtles and wading birds to increase
the diversity of gastropod communities by regulating the abundance of dominant species. Although the generalized diets of
most freshwater predators preclude tight co-evolutionary patterns of responses, there are combinations of predators that modify
gastropod behavior and shell morphology in aquatic assemblages of different ages and depths. This combination of invertebrate
and vertebrate predatory impacts led to competitive advantages among individual gastropods with different adaptations: (1)
less vulnerable shell morphologies and sizes; (2) predator-avoidance behaviors; or (3) rapid and widespread dispersal with
variable life histories. Some individuals develop thicker and/or narrow-opening shells or shells with spines and ridges. Other
thin-shelled species crawl out of the water or burrow to lower their risk to shell-breaking or shell-entering predators. Some
alter their age at first reproduction and grow rapidly into a size refuge. Fluctuations in water levels and introductions
of non-native species can change competitive dominance relationships among gastropods and result in major losses of native
species. Many different gastropod predators control species that are human disease vectors. Most snails and their predators
provide other ecosystem services such as nutrient cycling and transfer of energy to higher trophic levels. Their persistence
and diversity of native species require adaptive management and coordinated study.
KeywordsShell morphology-Aquatic insects-Leeches-Decapod crustaceans-Crabs-Crayfish-Fish-Omnivores-Invasive species-Disease ecology-Ancient lakes-Calcium-Water depth
"Adaptive radiation" is an evocative metaphor for explosive evolutionary divergence, which for over 100 years has given a powerful heuristic to countless scientists working on all types of organisms at all phylogenetic levels. However, success has come at the price of making "adaptive radiation" so vague that it can no longer reflect the detailed results yielded by powerful new phylogeny-based techniques that quantify continuous adaptive radiation variables such as speciation rate, phylogenetic tree shape, and morphological diversity. Attempts to shoehorn the results of these techniques into categorical "adaptive radiation: yes/no" schemes lead to reification, in which arbitrary quantitative thresholds are regarded as real. Our account of the life cycle of metaphors in science suggests that it is time to exchange the spent metaphor for new concepts that better represent the full range of diversity, disparity, and speciation rate across all of life.
The area of West Africa covered by this book includes eighteen countries : Mauritania, Senegal, The Gambia, Guinea Bissau, Guinea, Sierra Leone, Liberia, Côte d'Ivoire, Mali, Burkina Faso, Ghana, Togo, Benin, Niger, Nigeria, Chad, Cameroon and Equatorial Guinea (Bioko). Chad, Cameroon and part of Equatorial Guinea (Bioko) are usually treated as part of Central Africa rather than West Africa but these countries have been included because their freshwater crab faunas are principally West African in character (although endemic taxa and other species of Central African origin may also be represented in these countries). The West African faunal region is an informal subdivision of the Afrotropical (Ethiopian) zoogeographical region, and lies to the south of the European and Middle Eastern components of the Palaearctic zoogeographical region, where freshwater crabs of the genus #Potomon$ (family #Potamidae$, Ortmann, 1896) are found. The West African freshwater crab fauna includes at least thrity-two species in seven genera and one family. This fauna is arguably the most diverse in Africa and has a distinct character which differs greatly from that found elsewhere on the continent. The present work brings together recent contributions to the taxonomy, distribution, and ecology of the entire West African freshwater crab fauna (Bott, 1955, 1959, 1964, 1969a, 1970a ; Monod, 1977, 1980 ; Cumberlidge, 1985a, 1987, 1991a, 1993a,b,c, 1994a,b, 1995a,b,c,d, 1996a,b, 1999 ; Cumberlidge and Clark, 1992 ; Cumberlidge and Sachs, 1989a, 1991) and presents new information on phylogeny and biogeography. The past ten years or so have seen the establishment of two new genera (#Potamonemus$ Cumberlide and Clark, 1992 and #Louisea$ Cumberlidge, 1994) and the description of a number of new species from West Africa... (D'après résumé d'auteur)
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.
The genus Platythelphusa is revised and six species are recognized. These species are P. armata A. Milne-Edwards, 1887, P. maculata (Cunnington, 1899), P. conculata Cunnington, 1907, P. tuberculata Capart, 1952, P. polita Capart, 1952 and P. echinata Capart, 1952. A seventh taxon, P. denticulata Capart, 1952 is considered here to be a junior synonym of P. conculata. A diagnosis for each species is provided and most are figured from the type. Keys to the families of African freshwater crabs and to the genus Platythelphusa are also provided.
Fifty years ago, GE Hutchinson defined the ecological niche as a hypervolume in n-dimensional space with environmental variables as axes. Ecologists have recently developed renewed interest in the concept, and technological advances now allow us to use stable isotope analyses to quantify these niche dimensions. Analogously, we define the isotopic niche as an area (in δ-space) with isotopic values (δ-values) as coordinates. To make isotopic measurements comparable to other niche formulations, we propose transforming δ-space to p-space, where axes represent relative proportions of isotopically distinct resources incorporated into an animal's tissues. We illustrate the isotopic niche with two examples: the application of historic ecology to conservation biology and ontogenetic niche shifts. Sustaining renewed interest in the niche requires novel methods to measure the variables that define it. Stable isotope analyses are a natural, perhaps crucial, tool in contemporary studies of the ecological niche.
Data on the presence or absence of 25 fish species in a survey of 52 lakes from the watersheds of the Black and Hollow rivers of S- central Ontario were analyzed with 8 similarity coefficients. Co-occurrence coefficients reflect a general size effect similar to that commonly found in principal-components analysis. Measures of association and Ochiai's coefficient incorporate implicit centering transformations that reduce the size influence associated with the frequency of occurrence. Cluster analyses using co-occurrence coefficients are most susceptible to this size effect. The interpretations of many dendrograms fail to recognize size effects that arise from employing non-centered similarity coefficients. Arguments contrasting phenetic and phylogenetic methods may unknowingly debate the utility of centered versus non-centered coefficients, since the size effect undoubtedly contributes to the apparent strength of phylogenetic approaches. -from Authors
The rate of conversion of chlorophyll-a to phaeophytin-a in dilute acid organic solvents is markedly pH-dependent. The widely used spectrophotometric measurement before and after acidification to discriminate between chlorophyll-a and phaeopigments is applicable only between pH 2.6—2.8. At higher pH the reaction proceeds slowly and occasionally may be incomplete. At lower pH complicating reactions may occur, such as breakdown of certain carotenoid pigments causing (time-dependent) increase of background absorption, and formation of di-cations of phaeophytin with spectral characteristics different from the usually obtained mono-cations of phaeophytin. Consequently, it is stressed to control carefully the acid concentration, the water content of the solvent, and the amount of MgCO3 used in the filtration procedure. In general, for the purpose of spectrophotometric acidification experiments, acidification by dilute hydrochloric acid added to organic solvents containing 10—20% water, and omission of MgCO3 would be preferable.
On the basis of observed complications in the red part of the absorption spectrum of the pigment extract, it is recommended to use the above stated pH-range.
Sympatric speciation is a composite phenomenon requiring both ecological differentiation and the evolution of a mating structure that induces reproductive isolation. Ecological and sexual selection models have addressed these two aspects of sympatric speciation separately. We briefly discuss the recent results of these models and argue that the evolution of ecological and mating strategies are mutually dependent processes rather than independent phenomena corresponding to incompatible views of sympatric speciation. Then, we consider a combined model incorporating ecological interactions and sexual selection. In this model, sympatric speciation is initiated by si-multaneous evolutionary branching of ecological strategy, leading to ecological differentiation, and mating strategies, resulting in assortative mating. Both types of evolutionary branching can be understood as the outcome of a competition process in which individuals compete for a spectrum of either ecological resources or mating opportunities. Speciation is completed when a linkage disequilibrium between ecological and mating types splits the population into two ecologically differentiated and reproductively isolated groups. Using a combined analyti-cal and individual-based simulation approach, we illustrate the different dynamical regimes and characterize the necessary conditions for sympatric speciation in the model.
Paleorecords from multiple indicators of environmental change provide evidence for the interactions between climate, human alteration of watersheds and lake ecosystem processes at Lake Tanganyika, Africa, a lake renowned for its extraordinary biodiversity, endemism and fisheries. This paper synthesizes geochronology, sedimentology, paleoecology, geochemistry and hydrology studies comparing the history of deltaic deposits from watersheds of various sizes and deforestation disturbance levels along the eastern coast of the lake in Tanzania and Burundi. Intersite differences are related to climate change, differences in the histories of forested vs. deforested watersheds, differences related to regional patterns of deforestation, and differences related to interactions of deforestation and climate effects. Climate change is linked to variations in sediment accumulation rates, charcoal accumulation, lake level and water chemistry, especially during the arid-humid fluctuations of the latter part of the Little Ice Age. Differences between forested and deforested watersheds are manifested by major increases in sediment accumulation rates in the latter (outside the range of climatically driven variability and for the last 40years unprecedented in comparison with other records from the lake in the late Holocene), differences in eroded sediment and watershed stream composition, and compositional or diversity trends in lake faunal communities related to sediment inundation. Variability in regional patterns of deforestation is illustrated by the timing of transitions from numerous sedimentologic, paleoecologic and geochemical indicators. These data suggest that extensive watershed deforestation occurred as early as the late-18th to the early-19th centuries in the northern part of the Lake Tanganyika catchment, in the late-19th to early-20th centuries in the northern parts of modern-day Tanzania, and in the mid-20th century in central Tanzania. Rapid increases in sediment and charcoal accumulation rates, palynological and lake faunal changes occurred in the early-1960s. We interpret this to be the result of greatly enhanced flushing of sediments in previously deforested watersheds triggered by extraordinary rainfall in 1961/62. Regional differences in deforestation histories can be understood in light of the very different cultural and demographic histories of the northern and central parts of the lake shoreline. Incursion of slaving and ivory caravans from the Indian Ocean to the central coast of Lake Tanganyika by the early-19th century, with their attendant diseases, reduced human and elephant populations and therefore maintained forest cover in this region through the late-19th to early-20th centuries. In contrast, the northeastern portion of the lakeshore did not experience the effects of the caravan trades and consequently experienced high human population densities and widespread deforestation much earlier. These studies demonstrate the importance of paleolimnological data for making informed risk assessments of the potential effects of watershed deforestation on long-term lake ecosystem response in the Lake Tanganyika catchment. Differences in sediment yield and lake floor distribution of that yield, linked to factors such as watershed size, slope, and sediment retention, must be accounted for in management plans for both human occupation of currently forested watersheds and the development of future underwater reserves.
Studies of primate community structure increase our understanding of behavior, adaptation, and evolution. However, there are few biogeographic data on specific composition and association patterns in primate communities. I conducted a biogeographic analysis of the community structure of primate species at 16 sites in Guyana. I used data from 1725 km of line-transect censuses to determine specific composition and association patterns of 220 primate groups . Of the 18 polyspecific groups, 94.1% (N = 16) included squirrel monkeys. There was an overall trend towards positive specific associations among Guyanese primates. The only species that exhibited a negative pattern of interspecific associations were brown and wedge-capped capuchins. The sighting rate for wedge-capped capuchins at sympatric sites was particularly depressed compared to that for brown capuchins. Low plant productivity in Guyanese forests may reduce the diversity of feeding niches and result in a low incidence of polyspecific associations and scramble competition between wedge-capped and brown capuchins.
As biological invasions continue, interactions occur not only between invaders and natives, but increasingly new invaders
come into contact with previous invaders. Whilst this can lead to species replacements, co-existence may occur, but we lack
knowledge of processes driving such patterns. Since environmental heterogeneity can determine species richness and co-existence,
the present study examines habitat use and its mediation of the predatory interaction between invasive aquatic amphipods,
the Ponto-Caspian Dikerogammarus villosus and the N. American Gammarus tigrinus. In the Dutch Lake IJsselmeer, we found broad segregation of D. villosus and G. tigrinus by habitat type, the former predominating in the boulder zone and the latter in the soft sediment. However, the two species
co-exist in the boulder zone, both on the short and longer terms. We used an experimental simulation of habitat heterogeneity
and show that both species utilize crevices, different sized holes in a plastic grid, non-randomly. These amphipods appear
to optimise the use of holes with respect to their ‘C-shape’ body size. When placed together, D. villosus adults preyed on G. tigrinus adults and juveniles, while G. tigrinus adults preyed on D. villosus juveniles. Juveniles were also predators and both species were cannibalistic. However, the impact on G. tigrinus of the superior intraguild predator, D. villosus, was significantly reduced where experimental grids were present as compared to absent. This mitigation of intraguild predation
between the two species in complex habitats may explain the co-existence of these two invasive species.
A phylogenetic tree based on mitochondrial DNA (mtDNA) sequence data is presented that provides a basic framework for elucidating relationships of the endemic Tanganyikan freshwater gastropod genera Lavigeria and “Nov. gen.” (yet to be formally described). Analyses indicate that these two genera are sister taxa, yet their diversification patterns contrast markedly. Each contains definable species-level clades. The two species in the genus Nov. gen. are morphologically conservative and genetically divergent from each other and from lavigeria. The five species of lavigeria delineated in this analysis form a species flock. In comparison with Nov. gen., the Lavigeria flock is morphologically more variable both within and among species, but shows less genetic differentiation. Relationships within Lavigeria are resolved among the largest species, which form a single clade, but the basal taxon is still equivocal.
The Lake Tanganyika benthos presents a highly biodiverse system on many spatial scales. We present here an analysis of regional (gamma) diversity and local (alpha) diversity of the Lavigeria species flock, the most common and speciose of the endemic gastropods, across the currently accessible sections of lakeshore. We found significant differences in Lavigeria gastropod diversity among regions within the lake, and that regional species richness was strongly associated with the presence of local, short-range endemics. Species richness at individual sites was not correlated with total species richness of the surrounding region. Although sites frequently encompassed high sympatry of congeneric species, highly disjunct species distributions lead to non-predictable community assemblages.
The shells of most lacustrine gastropods are typically small, weakly calcified, and modestly ornamented to unornamented. Similarly, most lacustrine crabs are usually small detritivores with weak chelae. A number of invertebrate taxa in Lake Tanganyika, however, deviate from these generalities. This study explores a predator-prey coevolution model as an explanation for the large, heavily calcified, and ornate gastropods and the robust, durophagous crabs of Lake Tanganyika. The endemic thiarid and viviparid gastropods from Lake Tanganyika have significantly thicker shells and higher frequencies of terminal apertural lip thickening than closely related cosmopolitan taxa from outside the lake. Tanganyikan gastropods also display considerably higher incidence of shell repair, following nonlethal shell damage, than cosmopolitan taxa of the same families. There is a strong positive correlation between gastropod apertural lip thickness and shell repair frequency among all the gastropod species analyzed. The endemic Tanganyikan potamonautid crab Platytelphusa armata (a molluscivore) possesses larger, more robust crushing chelae than other African potamonautid or potamonid crabs. In contrast with the cosmopolitan African crabs, the Tanganyikan crabs display molariform, rather than serrate dentition on their crushing chelipeds. In shell-crushing experiments, the Tanganyikan gastropod shells were an order of magnitude stronger than typical lacustrine gastropod shells, many well within the range of tropical marine gastropod shell strengths. Predation experiments with the endemic gastropods Spekia, Neothauma, Lavigeria spp., Paramelania spp. and the crab Platytelphusa armata showed that increased size, apertural lip thickness or shell sculpture reduced the successful predation rate of P. armata. Crabs with large chelae have a greater ratio of successful: unsuccessful attacks than crabs with small chelae. Among cases of successful predation, crabs with large chelae employed predation methods that required less time and energy (such as crushing the shell in the cheliped) than the methods employed by crabs with small chelae (such as peeling the shell from the aperture or the spire). The morphological, shell-crushing, and aquarium experiment data, considered in concert, provide strong support for the idea that the endemic gastropods and crabs of Lake Tanganyika have coevolved over the past 7 million years.
Species that appear highly specialized on the basis of their phenotype (e.g., morphology, behavior, and physiology) also sometimes act as ecological generalists. This apparent paradox has been used to argue against the importance of competition as a diversifying evolutionary force. We provide an alternative explanation based on optimal foraging theory. Some resources are intrinsically easy to use and are widely preferred, while others require specialized phenotypic traits on the part of the consumer. This asymmetry allows optimally foraging consumers to evolve phenotypic specializations on nonpreferred resources without greatly compromising their ability to use preferred resources. The evolution of phenotypic specialization on nonpreferred resources can be driven by competition, but the specialists act as ecological generalists whenever their preferred resources are available. Our model identifies at least three different concepts of specialization that need to be distinguished, based on diet, prey utilization efficiencies, and phenotypic adaptations. The relationships among these concepts are complex and often counterintuitive. Specialists should often reject the very resources that they have evolved traits to use. The most extreme phenotypic specializations should occur in the absence of a trade‐off between using preferred and nonpreferred resources. Our model may explain why extreme phenotypic‐specializations evolve more often in fish communities than in terrestrial vertebrate communities and provides a mechanism whereby species can coexist in stable communities despite common preferences for some resources.
In this paper, the zoogeographical distribution of the Japanese soleoid fishes has been quantitatively investigated. The faunal characteristic of this group of fish at various representative localities extending from Japan to its adjoining region is first analysed by making use of SCHENCK et KEEN' method. The central latitude of each sole is represented by the mean velue of the northern and southern limits expressed by the geographical latitude. The biological latitude of each representative locality is the mean of the central latitudes of several species found there. The latitudinal change of the distributional index (D•1), which is the difference between the geographical and biological latitudes, is described as the faunal characteristic of each locality. The results obtained in this study are summarized as follows: 1. Based upon the central latitudes, the Japanese soles are made up of 3 forms, tropical, subtropical and temperate. Thus, the fish of which the central latitude is lower than 20 is called herein tropical form, which is represented by 7 species in Soleidae and 3 ones in Cynoglossidae. The subtropical form, defined here as one of which the latitude is about 30, contains 2 species in Soleidae and 5 ones in Cynogrossidae. The remaining 2 species of each family belong to the temperate form, of which the latituds is always higher than 33 (Tab. 1). 2. The latitudinal change of D•I in the Japanese soles found from Singapore or Kai to Muroran Prov. of Hokkaido or Uladivostok seems to be rather gradual, except for sudden change which takes place between Owashi (Mie Pref.) and Numazu (Shizuoka Pref.), and Hainan and Amoi, respectively (Fig. 2). 3. The point where the value of D•I becomes 0 is found to exist in latitudes 22°N in the Pacific and 27°N in the China Sea.
These species consisted of 3 major trophic groups: plankter feeders (2 species), benthic animal feeders (7), and piscivores (4) . Even within the same trophic group, feeding of a species differed from others in respect to the feeding site, feeding time and food item. Seven diurnal and territorial species consistently drove away other species that shared similar food items and feeding sites. Non-territorial species had larger home ranges than territorial ones and utilized the area fugitively. Piscivores and most benthic animal feeders had one or more characteristic and elaborated hunting techniques. Prey species were abundant but guarded themselves well against predators. Both the relationship among predatory species, which was not only competitive but also compensatory, and facultative commensalism among species of different species of different trophic groups were most responsible for the coexistence. -from Author
The taxonomy of the freshwater crabs of Tanzania, East Africa is revised based on a large collection of previously unreported material. The crabs are treated here as a distinct regional subset of the African continental fauna. We recognize 25 species belonging to three genera (Potamonautes MacLeay, 1838, Platythelphusa A. Milne-Edwards, 1872, and Deckenia Hilgendorf, 1869a) and three families (the Potamonautidae Bott, 1970, the Platythelphusidae Colosi, 1920, and the Deckeniidae Ortmann, 1897). Tanzania is home to fourteen species of Potamonautes (including one new species), 9 species of Platythelphusa and 2 species of Deckenia. These estimates can be expected to change as the taxonomy of the freshwater crabs of this region becomes more refined. Potamonautes unisulcatus (Rathbun, 1933) is removed from synonymy and is recognized as a valid species; P. platycentron (Hilgendorf, 1897), originally a subspecies of P. johnstoni (Miers, 1885), is regarded as a valid species; P. ambiguus (Rathbun, 1904) is treated here as a junior subjective synonym of P. johnstoni (Miers, 1885), and P. johnstoni stappersi (Balss, 1936) is treated as a junior subjective synonym of P. loveridgei (Rathbun, 1933). The present work adds another species of Potamonautes, P. xiphoidus n. sp. from Tanzania. A number of morphological characters (including the shape and size of the dorsal membrane of gonopod 1) are identified to help clarify the taxonomy of Potamonautes in Tanzania. A revised species list for Tanzania is provided, as well as updated identification keys to the families, genera and species of Tanzanian freshwater crabs. The distribution of each species is refined based on new localities. Three out of 25 species (12.5%) (P. infravallatus, P. unisulcatus and P. xiphoidus) are endemic to Tanzania, but this number rises to 13 out of 25 (52%) if the Lake Tanganyika endemic species which occur in other countries that border the lake are included. Only two of the 25 Tanzanian species of freshwater crabs (P. lirrangensis and P. suprasulcatus) occur outside of the East African region in the D. R. Congo and Malawi.
It is well known that coefficient of closeness (C=100c/√S1S2), which is the ratio of the number of common species (c) between two different localities to the geometric mean of their respective total number of species (S1, S2) proposed by OTSUKA, is useful in precisely comparing the faunistic feature between two different localities. With a view to our clarifying the distributional pattern of each species, degree of popularity (P) is newly defined herein in the following formula: P=N/S(n-1) Where, N stands for the frequency that one species is concurrently obtained together with other species of this group from the same locality in each zoogeographic division, n for the total number of species examined and S for the number of investigation. The results obtained are summarized as follows: (1) According to the coefficient of closeness among Nagasaki, Matsue, Maizuru, Niigata, Onomichi, Numazu, Kominato, Matsushima, Muroran, Owashi, Kochi and Kagoshima (Tab. 1), the Japanese waters can be divided into 5 faunal subdivisions. The southern part of Japan from Ryûkyû to Suruga Bay on the Pacific is geographically characterized by the fact that all Japanese soles including 7 tropical species never before found in any other part of Japan are unfailingly found there. The East China Sea is easily distinguished from other regions by the presence of characteristic species Zebrias fasciata. On the Japanese coast of the Japan Sea and the Pacific coast of the middle part of Japan (from Sagami-Nada to Kashima-Nada) several temperate and subtemperate soles are known. The fauna of the soles in the Inland Sea of Japan is of peculiar in character, being more or less influenced by the neighbouring fauna. But the northern part of Japan on the Pacific is the most sterile region, so far as soles are concerned, only 3 species (Areliscus interruptus, Zebrias japonicus and Rhinoplagusia japonica) being reported there. (2) The degree of popularity is large in Areliscus interruptus, Aseraggodes kobensis, Zebarias japonicus, Heteromycteris japonicus and Aesopia cornuta than in any other species found in the southern part of Japan on the Pacific (Tab. 2). On the Japanese coast of the Sea of Japan and the Pacific coast of middle part of Japan, the degree is large in Areliscus interruptus, Zebrias japonicus, Rhinoplagusia japonica and Areliscus joyneri (Tab. 3). (3) On the whole, the temperature and the subtropical forms of this group, whose degree of popularity is large, are widely distributed even to the northern part of the Japanese waters. But the tropical form has the degree usually smaller than 0.1, the northern limit of its range lying in the southern part of Japan.
The endemic thiarid and viviparid gastropods from Lake Tanganyika have significantly thicker shells and higher frequencies of terminal apertural lip thickening than closely related cosmopolitan taxa from outside the lake. Tanganyikan gastropods also display considerably higher incidence of shell repair, following nonlethal shell damage, than comspolitan taxa of the same families. The endemic Tanganyikan potamonautid crab Platytelphusa armata (a molluscivore) possesses larger, more robust crushing chelae than other African potamonautid or potamonid crabs. Experiments with the endemic gastropods Spekia, Neothauma, Lavigeria spp., Paramelania spp. and the crab Platytelphusa armata showed that increased size, apertural lip thickness or shell sculpture reduced the successful predation rate of P. armata. Crabs with large chelae have a greater ratio of successful:unsuccessful attacks than crabs with small chelae. Among cases of successful predation, crabs with large chelae used predation methods that required less time and energy than the methods used by crabs with small chelae. Data together provide strong support for the idea that the endemic gastropods and crabs of Lake Tanganyika have coevolved over the past 7 M yr. -from Authors
(1) Previous research into resource partitioning/competition has generally been limited to a pairwise inspection due to available methodologies. Here we describe a procedure that allows for a community perspective on the niche which is not limited to an analysis by pairs. (2) Multivariate statistical analyses, such as principal component analysis and principal coordinate analysis, can be used to create independent axes of resource utilization for a community. The niche hypervolume for each species is calculated from the product of the ranges of resource exploitations on each axis. This product defines a niche which is an n-dimensional rectangular parallelepiped (or n-box). (3) Formulas for the calculation of the intersection and total community niche hypervolume are presented. Minor modifications of these formulas allow for the calculation of the levels of intersection, where levels of intersection refer to how much a species' or community's space is overlapped, and by how many species. (4) We used these procedures to investigate the niche in a community of cyprinids.
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.
The taxonomically rich amphipod fauna of Lake Baikal (at present 257 described species and 74 subspecies) shows great ecological diversity and a variety of evolutionary directions. The main trends in the intralacustrine evolution of this group are: habitat partitioning by depth, substrate type or layer; trophic differentiation; differentiation by season of reproduction; transition to marsupial parasitism; the appearance of giant and dwarf forms; colonization of Baikal's gulfs; and geographical (allopatric) differentiation. Each of these ecological/evolutionary mechanisms operates at a different level in the taxonomic hierarchy. The prevalence of sympatric speciation in these amphipods is examined, and the occurrence of numerous cases of morphological convergence (parallelism) between Baikal and other, especially marine, amphipod faunas noted. Several examples of these parallelisms are given and are considered within the framework of nomogenetic evolution.
The rocky littoral areas of Lake Tanganyika harbor diverse fish communities, mainly composed of cichlids. Their stability, structure, and organizing mechanism were examined at three locations. These fish communities were stable, characterized by their persistence during a 10-yr period and resilience after a perturbation. Partitioning of spawning sites among substrate spawners was evident, which might be a factor in their ability to coexist. The fish communities were consistently composed of 12 food-habit groups, but composition of species in each group differed from location to location. Among species of different food-habit groups, facultative commensalisms were prevalent. Although aggressive interactions are common among fishes of the same food-habit group, each predatory fish obtained an advantage in feeding efficiency from the different feeding behaviors of other species of the same group. This mutaulism and the facultative commensalism should both increase species richness in different parts of the communities. -from Authors
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.
Acanthocyclus gayi Milne-Edwards et Lucas and A. hassleri Rathbun are two intertidal predatory crabs that coexist along the rocky coast of Chile. The two species are morphologically similar and remain hidden inside refuges during diurnal low tide periods. Their microhabitat distributions and diets were studied at two sites in central Chile. Juveniles of each species were found coexisting in three microhabitats (mussel beds, rock crevices and kelp holdfasts), although most lived amongst mid intertidal mussels. Most recruits were observed in mussel beds. In contrast to juveniles, adults were segregated by microhabitat. Most adults of A. hassleri were in galleries built through mussel beds, while adults of A. gayi were found only in rock crevices and holdfasts of the kelp Lessonia nigrescens Bory. Diets of both species were similar, even between adults. Because of the large dietary overlap observed between juveniles and adults of the two species, and the apparent abundance of food in the field, segregation between adult crabs did not seem to result from competition for food. Because thickness of the mussel bed was positively correlated with the density and size of crabs, there may be a paucity of suitable living spaces for adult crabs. In contrast to juvenile crabs, which shared refuges during low tides, adults aggressively defended refuges, both intra- and interspecifically. Laboratory and field experiments showed strong asymmetry in interspecific contests. Adults of A. hassleri, which have a proportionally larger master chela, were able to aggressively exclude adults of A. gayi from refuges provided in the laboratory, and from galleries in mussel beds in the field. Segregation between adult crabs seems to be the outcome of interference competition for refuges. Refuges are readily available for small crabs and hence they coexist in the same microhabitats.
Merits of the points and occurrence methods for measuring the relative importance of types of food eaten by four species of portunid crabs (Portunus pelagicus (Linnaeus, 1766), Thalamita crenata H. Milne Edwards 1834, T. danae Stimpson 1858, and T. sima H. Milne Edwards 1834) have been compared. Both methods describe different aspects of the relative importance of food items and the scores given by each were highly correlated for most types of food. The points method is unsuitable for foods which consist of a high proportion of soft tissue whereas the occurrence method is appropriate for most foods. Fewer types of food were found in nearly empty gastric mills than in full mills. A sample size of approximately 30 gastric mills, each at least 50% full, was determined empirically to be adequate for a description of natural diet.
An increasing number of statistical software packages offer exploratory data displays and summaries. For one of these, the graphical technique known as the boxplot, a selective survey of popular software packages revealed several definitions. These alternative constructions arise from different choices in computing quartiles and the fences that determine whether an observation is “outside” and thus plotted individually. We examine these alternatives and their consequences, discuss related background for boxplots (such as the probability that a sample contains one or more outside observations and the average proportion of outside observations in a sample), and offer recommendations that lead to a single standard form of the boxplot.
A comparative study was made of the seasonal variation in floristic composition of the diets selected by sheep and cattle grazing together on Agrostis-Festuca, Nardus and Molinia grassland communities in S Scotland. Sheep diets were more variable than cattle diets, both between and within animals, for all sites. Sheep and cattle differed significantly for almost all major dietary components; exceptions were Molinia leaf, grass sheath and dead material at the Molinia site. Differences between sheep and cattle diets were explicable by 1) a difference in the height at which the animals grazed in relation to differences in the distribution of plant species within the sward canopy. 2) the greater ability of sheep to select from fine-scale mixtures; and 3) the greater readiness of cattle to graze tall, more fibrous components. -from Authors
Ancient lakes have long been recognized as evolutionary theatres and hot spots of endemism; the evolution of their morphologically often highly diverse species flocks has received much attention. However, as each ancient lake has its own geological and evolutionary history, modes of speciation may differ from system to system. Ancient lakes can act as evolutionary reservoirs that assure the survival of relict species, but at the same time extant species may evolve through intralacustrine speciation. Other aspects of interest are the actual rates of immigration, diversification or extinction as well as the temporal framework of morphological change. Many of these questions have been addressed in the African (e.g. Lake Tanganyika) and Asian (e.g. Lake Baikal) ancient lakes. For an European ancient lakes (e.g. Lakes Ohrid and Prespa), such studies are largely missing. In the present paper, extraordinarily shaped endemic freshwater limpets of the genus Ancylus from the Balkan Lake Ohrid are used in a phylogeographic and phylogenetic context to test whether they represent an ancient lake species flock, to study the mode of speciation, and to assess the timing of morphological change. Based on DNA data from two mitochondrial genes (COI, LSU rDNA), it has been found that the Lake Ohrid Ancylus species form an endemic monophyletic group. In addition, the lake's feeder springs are inhabited by another, undescribed Ancylus species. All other studied waterbodies within the watershed do not support their own Ancylus lineages but are inhabited by a widespread Mediterranean taxon. The split between the species endemic to the lake and its sister taxon is dated to 1.4±0.6 million years ago. The study presents the first genetic confirmation for the existence of a species flock in a European ancient lake. Contrary to the prevailing opinion it shows that, concerning Ancylus, Lake Ohrid represents a site of intralacustrine speciation rather than an evolutionary reservoir. Moreover, it provides the first evidence for rapid morphological change in an European ancient lake species flock. See also Electronic Supplement at: http://www.senckenberg.de/odes/06-12.htm.
Two new species of Platythelphusa (Decapoda, Potamoidea, Platythelphusidae), are described from Lake Tanganyika. P. immaculata sp. nov. and P. praelongata sp. nov. are distinguished from congeners by a combination of diagnostic characters of the carapace, chelipeds, and pereiopods. Platythelphusa denticulata Capart, 1952, is removed from synonymy with P. conculcata . This brings the number of platythelphusid species reported from Lake Tanganyika to nine. A key is provided to separate the species of Platythelphusa.
French
Deux espèces nouvelles de Platythelphusa (Decapoda, Potamoidea, Platythelphusidae), sont décrites du lac Tanganyika. P. immaculata sp. nov. et P. praelongata sp. nov. se distinguent de leurs congénères par une combinaison de caractères diagnostiques concernant la carapace, les chélipèdes et les péréiopodes. Platythelphusa denticulata Capart, 1952 est retiré de la synonymie avec P. conculcata. Ceci porte le nombre des espèces de Platythelphusidae connues du lac Tanganyika à neuf. Une clé est fournie pour séparer les espèces de Platythelphusa.
Human impacts on aquatic biodiversity are often measured at the assemblage or community level, although it has been suggested that individual-level measures are more sensitive. We evaluated the effects of anthropogenic sedimentation on endemic snails in Lake Tanganyika, East Africa, by comparing assemblage-level (i.e., species richness, evenness, and abundance) and individual-level (i.e., frequencies of predation and parasitism, fecal organic content, life history) data between sediment-disturbed and reference sites. Previous studies have indicated that sedimentation kills snails and reduces mollusc diversity in this system, but we found little evidence of changes in species richness, evenness, or snail abundance at the levels of sedimentation recorded. In contrast, individual-level data revealed a variety of differences associated with sedimentation. Frequencies of shell scarring by predatory crabs and castration by parasitic trematodes were significantly lower at disturbed sites, indicating shifts in interspecific interactions. Snails ingested large amounts of inorganic sediments at disturbed sites, suggesting a reduction in food quality. In addition, sedimentation was associated with a large downward shift in size distribution within some species and reproduction at smaller size. These strong patterns in individual-level data contrast with the lack of effects at the assemblage level. We argue that incorporating individual-level measures will often enhance the sensitivity of impact surveys and may reveal effects of disturbance on important interspecific interactions.
Atyid prawns from Lake Tanganyika are still poorly understood. There are at least 11 species sharing an exceptionally small
size and a reduction in the number of branchiae. The majority are benthic although some are pelagic. This is reflected in
different morphologies of the body and walking legs. Morphological adaptions of the denticles on the chelipeds are adaptive
as they relate to different ways of feeding. Pelagic fish from Lake Malawi do not represent an example of sympatric speciation
as suggested by Shaw et al. (2000). It is more likely that several, independent radiations started from inshore generalists,
which gradually adapted to the openwater.
Fluvial bed sediments represent an important sink and source for a variety of organic and inorganic compounds. Their most important constituent is organic matter (OM) and its primary component organic carbon (OC). Few studies have been conducted in fluvial environments examining bed-associated OM or OC. This is surprising given the recent interest in global carbon cycling and the importance of bed-associated organics as ecosystem energy sources. The objective of this study was to examine the relationship between OM, determined by loss-on-ignition (LOI), and OC in fluvial bed sediments determined by a dry combustion analyzer. The wide adoption of the LOI method in soil science reflects its ease of use, it is inexpensive, it is rapid, requires no specialized training, and strong statistical relationships commonly exist between OM and OC estimated by standard dry combustion procedures. Regression models were developed between OC and OM for six bed sediment size fractions (≤2.0 mm) for 113 sample sites in a tropical stream on Oahu, Hawaii. All models were highly significant (p
Fishes associated with drifting seaweed were sampled in the Tohoku area, northwest Pacific, in late spring 1988, to analyse the community structure and ecological relationships of the dominant species.Seriola quinqueradiata Temminck et Schlegel was the dominant species and its escort was composed ofThamnaconus (Navodon)modestus, Sebastes inermis, Hyperoglyphe japonica andEnedrias nebulosus. E. nebulosus, which fed essentially on Gammarid crustaceans, was collected mainly in Sendai Bay; the other species, found in offshore water, were plankton feeders and did not exhibit any strong competition, indicating close cohabitation. The abundance of drifting seaweed in the Tohoku area peaked in May–June and decreased in July; they seemed to come from the nearest coast. JuvenileS. quinqueradiata (> 15 cm long) were collected with set nets in Sendai Bay during summer. They seemed to use drifting seaweed (along with the warm Kuroshio current) as a means of transportation during their migration from the southern spawning ground to northern Tohoku area. Drifting seaweed could be considered as a nursery, and the association of fishes with floating algae might have an influence on species recruitment.
The natural diet, rate of foregut clearance and diurnal activity of the crab Scylla serrata were determined. The gut volume is related to size of crab as gut volume (ml)=0.07e0.033x
, where x=carapace width in millimetres. Fifty per cent of crabs collected in Australia and South Africa contained molluscan remains and about 21% contained crustacean remains — chiefly grapsid crabs. Fish remains were rarely found, and it was concluded that S. serrata does not normally catch mobile forms such as fish and penaeid prawns. Gut clearance of organic tissue was rapid and almost complete after 12 h. Fish bone was retained for a mean time of 2 to 3 days, and shell for 5 to 6 days. Time-lapse photography, using infra-red light, was used to record activity. Visible light flashes reduced activity. S. serrata remained buried during the day, emerging at sunset to spend the night feeding, which occurred intermittently even when unlimited food was available. If no food was present the amount of time spent on the substrate surface was halved.
Ontogenetic changes in behaviour and habitat use of Jonah crabs Cancer borealis Stimpson were examined as part of a study on habitat competition between Jonah crabs and American lobsters Homarus americanus Milne-Edwards. Crabs, lobsters and predatory fish (Tautoga onitis Linnaeus) were placed in large circular tanks, each containing three “habitats”: cobble, featureless sand, and sand with shelter boxes. Two treatments of shelter availability were used: one shelter for every two decapods (limited) or two shelters per decapod (excess). Three size-classes of crabs (encompassing 65–158 mm carapace width) were tested with lobsters 49–59 mm carapace length.When excess shelter was available, crabs and lobsters occupied shelters significantly more frequently than the other habitats. When shelter availability was limited, crabs were displaced to other areas. The alternative habitat selected by crabs and the way in which they used it depended on crab size. Most small and medium crabs chose cobble, while large crabs were found equally in cobble and sand. Small crabs burrowed more deeply than large crabs, and burrowed more deeply in sand than in cobble. Interspecific aggressive interactions increased in intensity with crab size.T. onitis readily kill and consume Jonah crabs in tanks with no substratum or shelter. Based on the literature and my qualitative observations, I predicted that smaller crabs would be more vulnerable to predation than large crabs. However in my habitat choice experiments, crab mortality due to predation was low and was not related to crab size or habitat type. I hypothesize that size-dependent patterns of crab habitat use and behavior compensated for the greater vulnerability of smaller crabs.
Intraspecific modulatory multiplicity in the feeding mechanism of cichlids as elucidated by electromyography has profound implications on small-scale trophic events the sum of which is the very core of such large-scale population and evolutionary phenomena as efficiency of trophic exploitation niche width and overlap competition and adaptation. The greatest paradox emerging from the study on intra and interspecific differences in feeding repertoires of cichlid fishes is that the most specialized taxa are not only remarkable specialists in a narrow sense but also jacks-of-all-trades. If specialists are simultaneously jacks of-all-trades how could they have evolved according to the widely accepted hypothesis that broadening the range of usable resources prevents species from specializing on individual types? The organism can be considered to be composed of structural elements and functional components that exert mutual influences. As a result, a network of interacting constraints is set up. The nature of the network determines the direction and range of evolutionary changes the possibilities of optimizing adaptations and built-in variability of the trait. A change in the network can put a static trait into a different context to become dynamic. These changes in variability due to changes in the structure of the network cannot be explained in terms of simple adaptation to the external environment. Fitness is considered to depend on the nature of a network of interacting constraints. The possibilities of optimization the sensitivity of the phenotypic traits to environmental differences and the correlated evolutionary responses of different traits are all related to this network of interacting constraints between the elements and components of the organism. Thus the experimental and comparative studies of these networks of interacting constraints should become an increasingly more important focus for morphologists as they attempt to refine their understanding of adaptation.