Article

Morphological divergence within and between the Mexican sailfin mollies, Poecilia velifera and Poecilia petenensis

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  • El Colegio de la Frontera Sur, Chetumal, Mexico
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Abstract

This study examined the patterns of morphological variation both between species, and between sexes and among populations within each species of the Mexican sailfin mollies, Poecilia velifera and Poecilia petenensis, using geometric morphometrics and linear measure-ments of morphological traits. While sexes within each species differed in characteristics that may be important in sexual selection, such as length of the dorsal fin, species differed in traits, such as body depth, that may also be influenced by natural selection due to differences in habitats. Within each species, many morphological traits were similar among populations, but important differences, including caudal peduncle depth in P. petenensis (but not in P. velifera), suggested that habitat differences may also be important in shaping population divergence independently within each species. Indeed, the evolutionary vectors of male morphological population divergence for each species differed by an angle of 98Á5 , representing nearly orthogonal vectors and suggesting independent shape divergence between these two molly species. Finally, geographic isolation did not explain the morphological differentiation seen among populations, suggesting that natural and sexual selection were strong forces promoting morphological diversification within these two species, despite the potential for a high degree of population connectivity and gene flow.

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... First, quantifying the mating behavior repertoire of P. velifera and P. petenensis allows for a comparison with the other sailfin species, P. latipinna Ptacek & Travis 1996) and P. latipunctata (Ptacek et al. 2005). Second, P. velifera and P. petenensis vary in several morphological characteristics that could potentially influence their expression of behavioral polymorphisms, including differences in the range of male sizes at maturity and the size and shape of their exaggerated dorsal fin, i.e. sailfin, based on differences in the level of positive allometry between male standard length (SL) (tip of the snout to the end of the last vertebra) at maturity and dorsal fin size (Miller 1983;Schmitter-Soto 1998;Hankison et al. 2006). Specifically, our objectives in this study were to (1) characterize and compare mating behaviors both within and between two species of sailfin mollies, P. velifera and P. petenensis, and (2) determine whether differences in morphology within and between these species predict the degree of behavioral polymorphism that exists for each species. ...
... Males of all sailfin molly species vary in the range of male sizes at maturity Ptacek & Travis 1996;Ptacek et al. 2005;Hankison et al. 2006). Size at maturity for males is a fixed phenotype in mollies; once the anal fin has fused to form the gonopodium, little to no further growth in body length occurs. ...
... Male size at maturity is phenotypically correlated with the degree of exaggeration of the sailfin; larger males have relatively larger sailfins (Ptacek 2002;Hankison et al. 2006). In addition male size can influence the relative rates of two of the three male mating behaviors. ...
Article
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Polymorphism in male morphology is often correlated with the expression of alternate behavioral tactics. This relationship between behavioral and morphological polymorphisms, however, is less well understood. We characterized male mating behaviors and morphological variation within and between Poecilia velifera and P. petenensis to understand mating signal evolution in the sailfin molly lineage. In addition, we examined whether differences between these species in the size range of mature males and the strength of allometry between dorsal fin size and body length could explain the variation observed in their expression of different mating behaviors. We determined each male's mating behavior profile by observing the behavior of a single male in the presence of a receptive female. We found that P. velifera showed evidence of an alternate male mating strategy, with small males generally performing only gonopodial thrusts (forced insemination attempts) towards receptive females, while large males performed courtship displays as well as gonopodial thrusts. Males of P. petenensis performed similar rates of courtship displays and gonopodial thrusts regardless of body length. Little variation existed among populations of P. velifera in mating behaviors, while males from different populations of P. petenensis showed population-specific average rates of each mating behavior. Population differences in P. petenensis may be driven, in part, by its occurrence in more variable habitats than those occupied by P. velifera. Variation among individuals in the mating repertoire of P. velifera, but not P. petenensis, suggests that the greater range of variation in male size at maturity, as well as considerably stronger allometry between dorsal fin size and body length, may explain why males of P. velifera show the greatest degree of expression of alternate male mating behaviors when compared to other sailfin species. These results also suggest an important role of morphological polymorphisms in predicting the expression of alternate male mating behaviors.
... During a courtship display, males often erect the gonopodium and lower it approximately perpendicular to the body, in addition to expanding the dorsal fin (Rosen and Tucker, 1961), and such displays are also used in aggressive encounters between males (Baird, 1968;Travis, 1994). These morphological traits vary allometrically with male body size; larger males have disproportionately longer and higher dorsal fins and disproportionately shorter gonopodia (Ptacek, 1998(Ptacek, , 2002Hankison et al., 2006). As a result of the signalling function of these morphological features of male sailfin mollies, it is possible that positive phenotypic covariation in behaviour and morphology may have arisen as a result of female mating preferences, and such correlated changes in these signalling traits may have shaped species differences between sailfin and shortfin mollies in their mating systems. ...
... Variation in these traits can result in an increase or decrease in lateral projection area (the sum of body area and fin areas that encompass the lateral view of a male presented to a female during a courtship display), which has been shown to be an important target of sexual selection by female choice (Rosenthal and Evans, 1998;Karino and Matsunaga, 2002;MacLaren et al., 2004;Kozak et al., 2008). Variation in the length of the gonopodium has also been shown to exist between populations and species of poeciliid fishes (Kelly et al., 2000;Jennions and Kelly, 2002;Hankison et al., 2006), and females of one species preferred males with longer gonopodia (Langerhans et al., 2005). ...
... These morphological traits contributed most to species differences between sailfin and shortfin mollies. Five of these morphological differences (dorsal fin characters: length of dorsal fin, length of first dorsal fin ray, number of dorsal fin rays and depth of mid-body, as well as length of the gonopodium) are likely to be influenced by sexual selection (Rosenthal and Evans, 1998;Kelly et al., 2000;Jennions and Kelly, 2002;Karino and Matsunaga, 2002;MacLaren et al., 2004;Hankison et al., 2006;Kozak et al., 2008). Four morphological differences (caudal fin characters: height and length of the caudal fin, as well as body shape characteristics: depth of caudal peduncle and pre-anal distance) are likely to be shaped by natural selection (Webb, 1982(Webb, , 1984Endler, 1995;Ghalambor et al., 2003;Langerhans et al., 2003;Hankison et al., 2006). ...
Article
Premating reproductive isolation is a strong barrier to hybridization in natural populations, but little is known about the genetic mechanisms that allow changes in mating signals to develop and whether different components of a mating signal can evolve in concert when sexual selection favors phenotypic associations between them. In this study, we report results suggesting that changes in a behavioural trait (courtship display) and multiple phenotypically associated morphological traits (dorsal fin characters and length of the gonopodium) have contributed to divergence in mating signals used by sailfin mollies. Through the use of reciprocal F1 and backcross hybrids, we show that morphological traits important in separating sailfin from shortfin molly species have a genetic basis and are inherited in an autosomal, additive manner. We also report significant associations between the size of certain morphological traits (length of the dorsal fin and length of the gonopodium) and the tendency of males to perform courtship displays or gonopodial thrusts. In particular, higher courtship display rates were associated with increased dorsal fin length but decreased gonopodium length, characteristics most similar to sailfin species. Such phenotypic associations between different components of a mating signal suggest that selective forces can act in concert on multiple aspects of the signal, hence, promoting divergence and speciation in sailfin mollies.
... Within the derived sailfin molly lineage, two sister groups represent a split between freshwater species (Poecilia petenensis and Poecilia latipunctata) and salt marsh species (Poecilia velifera and Poecilia latipinna). While sexual selection has probably played an important role in divergence of sailfin mollies from shortfin ancestors (Ptacek 1998;Ptacek & Breden 1998), the four sailfin species have diverged primarily in allopatry and differences in local habitats in combination with female mating preferences have probably driven diversification and speciation (Hankison et al. 2006;Kozak et al. 2008). ...
... In this study, we test whether phenotypic divergence in morphological traits and mating behaviours is correlated with genetic divergence in order to infer the relative importance of selection, gene flow, and drift in the maintenance of population differences in the Mexican sailfin mollies, P. velifera and P. petenensis. We chose these species to examine the factors promoting and maintaining geographical variation in phenotypic traits because variation among populations occurs primarily in morphological and behavioural traits of males, which are associated with mating signals and swimming performance, and therefore, are likely targets of both natural and sexual selection (Hankison et al. 2006;Hankison & Ptacek 2007). In addition, these sailfin species from the Yucatán region of Mexico have a broad geographical range, occupying different geographical regions (sensu Wilson 1980;Schmitter-Soto et al. 2002) and habitat types (Schmitter-Soto 1998;Schmitter-Soto et al. 2002). ...
... The correlation between neutral genetic distance and phenotypic trait distance (morphology and behaviour; Table 1) was examined using Mantel tests (Mantel version 1.01; Bohonak 2002). Linear measures of morphological traits (16 for P. velifera, 19 for P. petenensis; see Hankison et al. 2006) were taken of males from all populations of P. velifera and from a subset of six populations (C1, C2, C3, T3, CH1, and QR4) for P. petenensis. Mahalanobis distance (a multivariate measure of distance) was calculated both for overall body shape measurements [size-transformed linear measures (ln trait length -ln standard length; Mosimann & James 1979;Farr et al. 1986;Ptacek & Travis 1996] and for dorsal fin characteristics and caudal fin characteristics. ...
Article
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Comparing the patterns of population divergence using both neutral genetic and phenotypic traits provides an opportunity to examine the relative importance of evolutionary mechanisms in shaping population differences. We used microsatellite markers to examine population genetic structure in the Mexican sailfin mollies Poecilia velifera and P. petenensis. We compared patterns of genetic structure and divergence to that in two types of phenotypic traits: morphological characters and mating behaviours. Populations within each species were genetically distinct, and conformed to a model of isolation by distance, with populations within different geographical regions being more genetically similar to one another than were populations from different regions. Bayesian clustering and barrier analyses provided additional support for population separation, especially between geographical regions. In contrast, none of the phenotypic traits showed any type of geographical pattern, and population divergence in these traits was uncorrelated with that found in neutral markers. There was also a weaker pattern of regional differences among geographical regions compared to neutral genetic divergence. These results suggest that while divergence in neutral traits is likely a product of population history and genetic drift, phenotypic divergence is governed by different mechanisms, such as natural and sexual selection, and arises at spatial scales independent from those of neutral markers.
... Morphological traits are often subject to strong natural and sexual selection, because they are the interface between organisms and their environment (Gatz 1979;McGill et al. 2006;Verberk et al. 2013;Bower and Piller 2015). Selection on morphological traits can vary across the ranges of species, inducing intraspecific morphological divergence among populations (Hankison et al. 2006). Such morphological divergence can be the result of either genetic divergence or phenotypic plasticity via natural selection or drift (Robinson and Wilson 1994;Nei 2007;Franssen et al. 2012), and these shifts can produce phenotypes that are better suited for the environment, increasing survival and fitness of these populations (Agrawal 2001;Parsons and Robinson 2006). ...
... In addition, biotic selective pressures, such as predation, are known to have profound effect on morphology (Vamosi and Schluter 2002;Langerhans et al. 2004;Langerhans 2009;Ingley et al. 2014). Intraspecific morphological variation has been commonly seen for many fish groups, including, but not limited to Poeciliidae (Hankison et al. 2006), Atherinopsidae (Krabbenhoft et al. 2009), Characidae (Langerhans et al. 2003), Cyprinodontidae (Collyer et al. 2005), Cyprinidae (Haas et al. 2010), and Cichlidae (Berbel-Filho et al. 2016). ...
Article
Selection on morphological traits can vary across the range of species, inducing a mosaic of phenotypes across populations. Intraspecific morphological divergence had been demonstrated for many fish groups inhabiting environments with varying abiotic or biotic selective pressures. Such intraspecific phenotypic variation can have a strong influence on the ecologies of species. In the current study, we examined patterns of intraspecific morphological divergence between two populations of Sarotherodon melanotheron and Coptodon guineensis in Lake Ahémé and Porto-Novo lagoon, Benin. Using multiple morphological traits, we demonstrated intraspecific morphological divergence between Lake Ahémé and Porto-Novo lagoon for these species. However, evidence for parallel divergence was found for these two species, implying a similar response to selective pressures might have been acting on labile traits. In addition, species specific morphological changes observed in the current study might be because of differing responses to similar selective forces or taxon-specific selective forces acting on labile traits. The intraspecific trait divergence demonstrated in the current study suggests several possible selective pressures acting on these populations, yet the cause of this divergence remains unknown and additional studies are required to test these inferences.
... The Yucatan molly, Poecilia velifera (Regan, 1914) (Figure 1), is a member of the Poeciliidae, a large family of small-bodied fishes native to fresh and brackish waters of the New World. P. velifera is from Central America and native to the Yucatan Peninsula, Mexico (Hankison et al. 2006), where it typically occurs in coastal brackish waters of Campeche, Yucatan and Quintana Roo City, and the nearby islands of Mujeres and Cozumel (Miller 1983). It has been introduced to many countries around the world via the aquarium fish trade and also as a biological control agent for insects, especially mosquitoes (Courtenay and Meffe 1989;Lever 1996). ...
... The present study found that Poecilia velifera prefers near-shore, highly vegetated shallow habitats characterized by little or no water current, similar to conditions described by Courtenay and Meffe (1989) and Hankison et al. (2006). During our survey of the Songkhla Lagoon coast we found these types of habitat to be common throughout the shoreline of the Lagoon, including areas not yet invaded in Thale Sap, Thale Luang and Thale Noi. ...
Article
A non-native fish, the Yucatan molly Poecilia velifera (Regan, 1914), has recently become established in the Songkhla Lake Basin, south Thailand. Based on our field surveys in December 2007, we conclude that this species is present only in the Haad-kaew Lagoon and the southernmost part of the Songkhla Lagoon, the Thale Sap Songkhla. We sampled P. velifera monthly for 13 months (January 2007-January 2008), using beach seine and cast net, to obtain information on its population structure, morphology and reproduction. It was found that male and female P. velifera became sexually mature at 16.8 and 17.1 mm standard length, respectively. The overall sex ratio of males to females was 1.0:1.8. However, the proportion of males was less within specimens belonging to larger size classes. P. velifera reproduced continuously throughout the year but with two peaks, one in March-May and another in August-December.
... Here constraints on sailfin size and shape for improved swimming performance and increased reliance on courtship displays to attract females may help to explain weaker preferences by females of this species for larger males. Indeed, morphological studies have shown that interpopulation variation in males of P. petenensis is greatest for characteristics of the caudal peduncle and caudal fin (both affect thrust and swimming speed ;Webb 1978;Domenici 2003) whereas populations of P. velifera males vary most with respect to size and shape of the dorsal fin ( Hankison et al. 2006). In addition, courtship display rates are higher in P. petenensis than P. velifera, and females might use courtship for more reliable mate recognition in turbid, fast-flowing habitats (Hankison and Ptacek 2007). ...
... Significant preferences for conspecific males when paired with shortfin males may have been due to discrimination against males of P. mexicana, a species that females of P. petenensis must regularly avoid heterospecific matings with. As a result of reinforcement of mating preferences in sympatry, females of P. petenensis may discriminate more strongly against ''small'' males; indeed males of P. petenensis less than 35 mm SL are almost nonexistent in natural populations ( Hankison et al. 2006;Hankison and Ptacek 2007). ...
Article
We tested whether sexually selected morphological traits in the sailfin mollies, Poecilia velifera and Poecilia petenensis, are also used in species recognition. Our first experiment, using live males as stimuli and providing females with olfactory as well as visual cues, found that females of both sailfin species preferred conspecific males to males of shortfin species. However, neither species preferred conspecific males when compared with heterospecific sailfin males, suggesting that premating reproductive isolation is not well developed between them. Our second experiment, providing females with only visual cues when distinguishing between live males, found that females of P. velifera preferred the larger of 2 stimulus males, regardless of whether the larger male was a conspecific or an heterospecific sailfin male. Such a preference for the larger sized male was not found in P. petenensis. To further investigate the role of the dorsal “sailfin” in species recognition, we used model males that varied only in the species identity of their dorsal fins. Females of both sailfin species preferred conspecific models with conspecific sailfins to those with dorsal fins of the shortfin species. In addition, females of P. velifera preferred the model with the largest sailfin, regardless of species identity. Similarly to the live male experiments, females of P. petenensis did not distinguish between conspecific and heterospecific sailfins. Overall, our study suggests that females of P. velifera have a generalized preference for larger males and that species-specific differences in sailfin shape do not lead to premating reproductive isolation between these 2 sailfin species.
... Poecilia velifera (Regan, 1914), conhecida popularmente como molinésia velifera, é originária da Península de Yucatán no México, onde habita ambientes mais quentes do que as outras espécies de molinésias, com temperaturas entre os 25° e os 28°C (Hankison et al., 2006;Moraes et al., 2017). Poecilia vivipara Bloch, Schneider, 1801 foi originalmente descrita do Suriname (Lucinda, 2003), sendo principalmente encontrada em ambientes lênticos, com salinidade variando de água-doce até condições hipersalinas (Gomes-Jr., ...
... Además, le permiten al animal tener respuestas rápidas a los cambios ambientales, al generar diferentes fenotipos en una especie, sin realizar cambios en el genoma, lo que facilita su adaptabilidad. Pueden actuar tanto factores bióticos como abióticos: profundidad, distribución, edad, ambientes contrastantes, entre otros (Hankison et al., 2006;Haas et al., 2010). ...
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Centro de Investigaciones Marinas Universidad de La Habana revista de investigaciones marinas ARTICULO ORIGINAL OsteOlOgía descriptiva y cOmparada de lOs huesOs premaxilar y dentariO de cuatrO especies de peces óseOs frecuentes en el registrO arqueOlógicO de cuba Descriptive and comparative osteology of premaxillary and dentary bones of four frequent bony fish species in the archaeological record of Cuba RESUMEN En la actualidad Cuba no cuenta con una colección osteológica lo suficientemente representativa de los peces que moran sus aguas, lo cual constituye una barrera en la realización de estudios de iden-tificación, sistemática e ictioarqueología. En Cuba son muy pocos los trabajos que tratan sobre la osteología de los peces óseos. Los objetivos del presente trabajo son describir los caracteres osteológi-cos de los huesos premaxilar y dentario en cuatro especies de peces marinos que son frecuentemente hallados en sitios arqueológicos de Cuba; y comparar los huesos mencionados entre las especies objeto de estudio teniendo en cuenta las variaciones morfológicas. Se ini-ció la creación de una colección osteológica craneal de peces óseos frecuentes en aguas cubanas. Se seleccionaron las especies: Lutja-nus analis, Epinephelus striatus, Mycteroperca venenosa y Sphyrae-na barracuda, por su incidencia en el registro ictioarqueológico del país. Se utilizaron los huesos premaxilar y dentario, por su alta variabilidad entre especies y resistencia al paso del tiempo en los sitios arqueológicos. Las descripciones osteológicas de los premaxi-lares y los dentarios posibilitaron la determinación de caracteres discriminantes para la identificación de las cuatro especies. Las es-pecies estudiadas se pueden diferenciar a partir de la forma, tama-ño y dirección de los procesos ascendentes, articular y maxilar, per-tenecientes al hueso premaxilar; y la articulación entre las ramas, la dentición y la presencia de escotaduras en el dentario.
... Poecilia velifera (Regan, 1914), conhecida popularmente como molinésia velifera, é originária da Península de Yucatán no México, onde habita ambientes mais quentes do que as outras espécies de molinésias, com temperaturas entre os 25° e os 28°C (Hankison et al., 2006;Moraes et al., 2017). Poecilia vivipara Bloch, Schneider, 1801 foi originalmente descrita do Suriname (Lucinda, 2003), sendo principalmente encontrada em ambientes lênticos, com salinidade variando de água-doce até condições hipersalinas (Gomes-Jr., ...
... Poecilia velifera (Regan, 1914), conhecida popularmente como molinésia velifera, é originária da Península de Yucatán no México, onde habita ambientes mais quentes do que as outras espécies de molinésias, com temperaturas entre os 25° e os 28°C (Hankison et al., 2006;Moraes et al., 2017). Poecilia vivipara Bloch, Schneider, 1801 foi originalmente descrita do Suriname (Lucinda, 2003), sendo principalmente encontrada em ambientes lênticos, com salinidade variando de água-doce até condições hipersalinas (Gomes-Jr., ...
... Five years later, personnel from the Laboratorio de Zoología, Facultad de Ciencias Naturales, UNACAR performed monitoring to determine the abundance and distribution of the fish sailfin molly (Poecilia velifera) to evaluate the restoration progress within that area (unpublished data). This fish species is endemic to the Yucatán Peninsula, restricted to coastal habitats, particularly those with low flow regimes, such as anchialine cenotes and salt marshes, where the fish are prey of fish, birds, and crocodiles [18]. Fish were not specifically collected for parasitological analysis; however, we were allowed to examine some samples. ...
Article
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Abstract Fish harbor a high diversity of parasites that play an important role for the ecosystem. Because these parasites have different life-cycle traits, changes in their populations or communities may provide useful information related to ecosystem health. Highly stressful conditions may reduce parasite communities or populations. However, it is not a rule since host-parasite interactions are hardly predictable. In this study, macroparasites of the fish sailfin molly (Poecilia velifera) from three sites (conserved, degraded and under restoration) located within a mangrove wetland area, in the Terminos Lagoon (southern Gulf of Mexico), were analyzed in order to determine their potential use as bioindicators. A total of 198 fish were examined for parasites. Six parasite species were found: two crustaceans (Argulus sp. and Ergasilus aff. cerastes), one trematode (Centrocestus formosanus), one monogenean (Gyrodactylus sp.) and two nematodes (Contracaecum sp. and Cuculanus sp.). There were no significant differences in the structure of parasite infracommunities as well as in prevalence and intensity of parasite populations between degraded and conserved sites. However, the site under restoration had poorer infracommunities and smaller populations of crustaceans and trematodes, which suggests that restoration efforts have not improved the ecological conditions. Based on these results, it is conjectured that parasites of P. velifera did not show useful information to provide a diagnosis related to ecosystem health. Beyond this ecological subject, the present study represents new host record for most parasite species found.
... In these analyses, for each species (or for each behavior in S. stimpsoni), the 101 mean values of each variable (calculated for each 1% increment through the kinematic cycle) were used to generate vectors with 101 dimensions. The angle between pairs of these vectors could then be calculated using standard equations [36][37][38]. An angle near 0u indicates two nearly identical vectors (i.e., two nearly identical kinematic profiles), whereas an angle near 90u indicates perpendicular trajectories (profiles that are not correlated, or are independent of each other). ...
... In this study, males have longer and more pointed anal fins, and longer, larger and more pointed dorsal fins than females. Sexual dimorphism in anal and dorsal fin traits is common in fishes, and these differences are thought to emerge due to male-male competition and female choice (Oliveira & Almada, 1995;Kottelat & Lim, 1999;Hankinson et al., 2006;McGrath & Hilton, 2012). Likewise, in F. notatus, the sexual dimorphism in anal or dorsal fin size and shape is believed to be due to their sex-specific uses in courtship and spawning (Carranza & Winn, 1954;Foster, 1967). ...
Article
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The size and shape of the anal and dorsal fin in the blackstripe topminnow Fundulus notatus from lake and stream habitats across multiple ages and sexes were examined. Differences in the size and shape of anal and dorsal fins were sex-specific and not related to habitat differences.Males have longer and more pointed anal fins and longer, larger and more pointed dorsal fins than females. These sex differences occur predominantly in the older age class. The angle (i.e. pointedness) of the dorsal and anal fins is tightly correlated suggesting that fins follow a similar growth trajectory as individuals become sexually mature.
... For example, males of P. latipunctata from the natural population used in this study ranged in SL from 23 to 46 mm. In comparison, males of P. velifera range in SL at maturity from 19 to 84 mm and males of P. petenensis in SL from 33 to 110 mm [53,54]. Male size at maturity in mollies is thought to be controlled by a similar Y-linked genetic architecture as that found in Xiphophorus (P locus system described by [55,56]) producing a normal distribution of male sizes in natural populations, with sons maturing at nearly identical sizes to those of their fathers [57]. ...
Article
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A phylogenetic comparative approach was used to examine the evolution of the enlarged “sailfin,” characteristic of the monophyletic lineage of sailfin mollies (Poecilia: Mollienesia), but absent in one of its species, P. latipunctata. Ancestral character state reconstructions demonstrated that the ancestral sailfin molly possessed the enlarged sailfin, and, thus, males of P. latipunctata have secondarily lost this trait. The strength of female mating preference was measured in P. latipunctata for two known targets of sexual selection, large male size, and sailfin male phenotype. Females of P. latipunctata preferred conspecific males of larger body size to those of smaller body size, but showed no preference for sailfin males of a related species, P. velifera, when compared with males of the shortfin species, P. mexicana. Taken together, these results suggest that the targets of sexual selection may have shifted in this species and that reduction in female preference for sailfin males may have played a role in the loss of this ornament.
... These variables included the timing of the peak net GRF, magnitudes of the components of GRF, and angles of GRF orientation. Second, vector analysis (Hankison et al. 2006;Cullen et al. 2013;Rivera et al. 2013) was used to qualitatively assess the overall similarity of GRF patterns between pairs of appendicular systems. For each trace of force values through stance, 21 mean values of the variable (calculated for each 5% increment through stance, from 0% to 100%) were used to generate vectors with 21 dimensions. ...
Article
The invasion of land was a pivotal event in vertebrate evolution that was associated with major appendicular modifications. Although fossils indicate that the evolution of fundamentally limb-like appendages likely occurred in aquatic environments, the functional consequences of using early digited limbs, rather than fins, for terrestrial propulsion have had little empirical investigation. Paleontological and experimental analyses both have led to the proposal of an early origin of "hind limb-driven" locomotion among tetrapods or their ancestors. However, the retention of a pectoral appendage that had already developed terrestrial adaptations has been proposed for some taxa, and few data are available from extant functional models that can provide a foundation for evaluating the relative contributions of pectoral and pelvic appendages to terrestrial support among early stem tetrapods. To examine these aspects of vertebrate locomotor evolution during the invasion of land, we measured three-dimensional ground reaction forces (GRFs) produced by isolated pectoral fins of mudskipper fishes (Periophthalmus barbarus) during terrestrial crutching, and compared these to isolated walking footfalls by the forelimbs and hind limbs of tiger salamanders (Ambystoma tigrinum), a species with subequally-sized limbs that facilitate comparisons to early tetrapods. Pectoral appendages of salamanders and mudskippers exhibited numerous differences in GRFs. Compared with salamander forelimbs, isolated fins of mudskippers bear lower vertical magnitudes of GRFs (as a proportion of body weight), and had GRFs that were oriented more medially. Comparing the salamanders' forelimbs and hind limbs, although the peak net GRF occurs later in stance for the forelimb, both limbs experience nearly identical mediolateral and vertical components of GRF, suggesting comparable contributions to support. Thus, forelimbs could also have played a significant locomotor role among basal tetrapods that had limbs of sub-equal size. However, the salamander hind limb and mudskipper pectoral fin had a greater acceleratory role than did the salamander forelimb. Together, data from these extant taxa help to clarify how structural change may have influenced locomotor function through the evolutionary invasion of land by vertebrates.
... In these analyses, for each species (or for each behavior in S. stimpsoni), the 101 mean values of each variable (calculated for each 1% increment through the kinematic cycle) were used to generate vectors with 101 dimensions. The angle between pairs of these vectors could then be calculated using standard equations[36][37][38]. An angle near 0u indicates two nearly identical vectors (i.e., two nearly identical kinematic profiles), whereas an angle near 90u indicates perpendicular trajectories (profiles that are not correlated, or are independent of each other). ...
Article
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Species exposed to extreme environments often exhibit distinctive traits that help meet the demands of such habitats. Such traits could evolve independently, but under intense selective pressures of extreme environments some existing structures or behaviors might be coopted to meet specialized demands, evolving via the process of exaptation. We evaluated the potential for exaptation to have operated in the evolution of novel behaviors of the waterfall-climbing gobiid fish genus Sicyopterus. These fish use an "inching" behavior to climb waterfalls, in which an oral sucker is cyclically protruded and attached to the climbing surface. They also exhibit a distinctive feeding behavior, in which the premaxilla is cyclically protruded to scrape diatoms from the substrate. Given the similarity of these patterns, we hypothesized that one might have been coopted from the other. To evaluate this, we filmed climbing and feeding in Sicyopterus stimpsoni from Hawai'i, and measured oral kinematics for two comparisons. First, we compared feeding kinematics of S. stimpsoni with those for two suction feeding gobiids (Awaous guamensis and Lentipes concolor), assessing what novel jaw movements were required for algal grazing. Second, we quantified the similarity of oral kinematics between feeding and climbing in S. stimpsoni, evaluating the potential for either to represent an exaptation from the other. Premaxillary movements showed the greatest differences between scraping and suction feeding taxa. Between feeding and climbing, overall profiles of oral kinematics matched closely for most variables in S. stimpsoni, with only a few showing significant differences in maximum values. Although current data cannot resolve whether oral movements for climbing were coopted from feeding, or feeding movements coopted from climbing, similarities between feeding and climbing kinematics in S. stimpsoni are consistent with evidence of exaptation, with modifications, between these behaviors. Such comparisons can provide insight into the evolutionary mechanisms facilitating exploitation of extreme habitats.
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Studies addressing the adaptive significance of female ornamentation have gained ground recently. However, the expression of female ornaments in relation to body size, known as trait allometry, still remains unexplored. Here, we investigated the allometry of a conspicuous female ornament in Pelvicachromis taeniatus, a biparental cichlid that shows mutual mate choice and ornamentation. Females feature an eye-catching pelvic fin greatly differing from that of males. We show that allometry of the female pelvic fin is scaled more positively in comparison to other fins. The pelvic fin exhibits isometry, whereas the other fins (except the caudal fin) show negative allometry. The size of the pelvic fin might be exaggerated by male choice because males prefer female stimuli that show a larger extension of the trait. Female pelvic fin size is correlated with individual condition, suggesting that males can assess direct and indirect benefits. The absence of positive ornament allometry might be a result of sexual selection constricted by natural selection: fins are related to locomotion and thus may be subject to viability selection. Our study provides evidence that male mate choice might scale the expression of a female sexual ornament, and therefore has implications for the understanding of the relationship of female sexual traits with body size in species with conventional sex-roles.
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Variation among individuals in the expression of behaviors and associations of behaviors in different contexts can lead to the maintenance of behavioral polymorphisms. Individual variation in morphology is often associated with behavioral polymorphism, yet the degree to which morphology predicts behavioral phenotype is not well understood. We measured individual variation in size and behaviors in the sailfin molly, Poecilia latipinna, by comparing the behavior of individual males of different sizes across four different contexts (mating, exploratory tendency, sociability, and predator inspection). We also investigated the degree to which male size, a fixed genetic trait, influenced the expression of each behavior and associations between behaviors. We found that male mollies show strong associations between certain behaviors and only some of these are predicted by male size. For example, size has a strong influence on the courtship‐boldness axis with larger males showing higher rates of courtship displays and being bolder in predator inspection. A positive association was found between exploratory tendency, sociability, and gonopodial thrusting rates, yet the expression of these behaviors was independent of male size. Thus, sailfin mollies, like many fish species, show associations of behaviors that contribute to differences among males in personality type. The fixed genetic effect of male size at maturity influences courtship and boldness, but individual variation in exploratory tendency, sociability, and sneak copulation attempts through gonopodial thrusts is independent of male size. Such variation among males in behavioral associations within and between different contexts may slow the rate at which populations of P. latipinna can diverge in individual behaviors.
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Poeciliids are of particular interest to conservation biologists for a number of reasons. First, they have become excellent models for conservation biologists due to their small size and rapid generation time (Quattro & Vrijenhoek 1989; Leberg 1990, 1993). Second, many poeciliid studies have provided important insights on the rate of evolutionary diversification (e.g., Endler 1980; Reznick et al. 1990; Reznick et al. 1997; see also Pires et al., chapter 3; Breden & Lindholm, chapter 22; Grether & Kolluru, chapter 6; Johnson & Bagley, chap-ter 4; Schlupp & Riesch, chapter 5), the ultimate source of biodiversity. Third, poeciliids are vulnerable to the same anthropogenic factors driving the current extinction crisis (e.g., habitat loss, invasive species). Paradoxically, one of the greatest threats to poeciliids is the spread of heterospecifi c poeciliids (Minckley & Deacon 1968; Meffe 1985b; Minckley & Jensen 1985; Courtenay & Meffe 1989; Belk & Lydeard 1994). Thus, poeciliids have been extensively evaluated in the context of conservation biology (Johnson & Hubbs 1989; Leberg 1990, 1993; Stockwell et al. 1996; Stockwell & Weeks 1999). Johnson and Hubbs (1989) provided an overview of the conservation status of the poeciliids in the United States. Since that time, poeciliids have mirrored the decline of other freshwater fishes (see Jelks et al. 2008). Furthermore, our understanding of relationships among taxa has increased, allowing reevaluation of the systematics and distribution of poeciliid biodiversity (Rosen & Bailey 1963; Parenti 1981; Parenti & Rauchenberger 1989; Hrbek et al. 2007). Much applied research has focused on endangered poeciliids (e.g., Poeciliopsis spp.) as well as common and invasive poeciliids (e.g., Gambusia spp., Poecilia reticulata). In fact, many poeciliids have been used as model systems to examine questions central to the field of conservation biology. Here, we provide an overview of the poeciliids from the perspective of conservation biology. First, we review the geographic distribution of poeciliid biodiversity as well as associated threats. We then consider the impact of nonnative poeciliids on native species and ecosystems. We conclude by summarizing the role of selected poeciliid species as models for studies in the emerging fi eld of evolutionary conservation biology (as conceptualized by Ferrière et al. 2004).
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We examined intra- and interspecific variability in shape of three topminnow species (Funduluidae: Fundulus notatus, F. olivaceus, and F. euryzonus) across ten drainages. Within each drainage, five or more adult male topminnows were digitized at multiple sites (83 total sites) along the river continuum representing a range of stream sizes (cumulative drainage area) and hydrological conditions. Nine of the ten drainages contained two Fundulus species that were longitudinally separated along the river continuum with narrow areas of coexistence. Upstream–downstream distribution patterns were variable by drainage, allowing us to examine patterns repeated across ecologically similar species. More variability in shape was explained by drainage (19.7%) than by species (7.4%) differences. Populations of F. notatus from headwaters (three drainages) converged on a deep-bodied form similar to F. olivaceus which was typically sampled in headwaters. Fundulus notatus shape was more closely related to stream size than in the other two species. Headwater populations of F. notatus and F. olivaceus had fineness ratios near the hydrodynamic optima of 4.5 whereas downstream populations of F. notatus had shallower bodies. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103, 612–621.
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Divergence in mating signals is a primary factor leading to reproductive isolation, and thus, speciation. However, the genetic changes underlying such divergence are poorly understood, especially in vertebrates. We used two species of poeciliid fishes, Poecilia velifera and P. mexicana, to explore the link between genes and mating behaviors that has resulted in pre-mating reproductive isolation between these species. Using backcross hybrids created from the F1 male offspring of reciprocal interspecific crosses between a sailfin molly (P. velifera) and a shortfin molly (P. mexicana), we examined the effects of Y-linkage and autosomal contributions on the expression of two male mating behaviors: courtship displays and gonopodial thrusts. The F1 hybrid males displayed a strong influence of sire on courtship display rates, with F1 males sired by the sailfin species showing courtship display rates that were up to three times higher than the rates of displays performed by F1 males sired by the shortfin species. These results suggest a Y-linked genetic effect on the expression of courtship display behavior. Comparisons between backcross hybrid males with sailfin Y-chromosomes or shortfin Y-chromosomes suggested that the interaction of autosomal genes also influences the inheritance of courtship display rates. Sailfin autosomal genes significantly increased the probability of performing courtship displays for hybrid males, and increased display rate for males from the sailfin Y-chromosome line. Autosomal genes had less of an impact on gonopodial thrusting behavior, however, thrust rates did significantly decrease with an increasing proportion of sailfin autosomes in males from the shortfin Y-chromosome line. These results suggest that the inheritance of species differences in mating signals between shortfin and sailfin mollies involves both genes found on the Y-chromosome and autosomal gene influences on their expression.
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Morphological variations of the serranid fish Cephalopholis taeniops were studied in relation to habitat fragmentation in the Cape Verde Archipelago. While a significant allometric effect existed (11·5% of total body-shape variation), differences in morphology associated with sex and ontogeny were not significant. MANOVA followed by CVA showed that each island presented a particular allometric pattern. Average body shape for all islands was well discriminated with CVA models. Pair-wise comparisons of the ontogeny of morphological change between islands revealed that northern islands (Santo Antão, São Vicente and Santa Luzia) along with Boavista Island showed a similar direction in shape ontogeny, while all other paired comparisons indicated different ontogenetic patterns. When comparing directions of inter-population shape changes, individuals from Fogo Island, the southernmost locality, departed far from the orthogonal relation, suggesting that they were undergoing independent body-shape trajectories. Physical isolation by geographic distance and depth was positively correlated with morphological divergence among populations from different islands. This finding supports the hypothesis that habitat fragmentation in the Cape Verde Archipelago can be interpreted in terms of marine population structure.
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Female mate preference for dorsal fin length in male guppies (Poecilia reticulata) was investigated. In a dichotomous choice experiment using live males, females preferred males with longer dorsal fins to those with shorter dorsal fins. When the dorsal fin lengths of the two males were reversed by surgical manipulation, the females reversed their preference. To further examine this preference behaviour, a second dichotomous choice experiment was conducted using digitally modified male images that differed only in dorsal fin lengths. In this next experiment, females preferred male images with a longer dorsal fin than those with a shorter dorsal fin. In order to clarify the cost of possessing a long dorsal fin for males, the effect of dorsal fin length on swimming performance of males was also examined with a flow chamber. Male swimming performance was enhanced by surgically shortening the dorsal fin. The result of this study suggests that the long dorsal fin of male guppies is a costly handicap that may have evolved due to female mate choice. KeywordsFemale mate choice–Fin length–Male ornament– Poecilia reticulata –Sexual selection–Swimming performance
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W hen correlations among a set of traits within a species strongly resemble the correlations among these same traits across species, it is tempting to explain the origin of the interspecific pattern by the same mech-anisms that are observed to maintain the intraspecific pattern (Travis 1994a). In this note we suggest that it is necessary to consider a variety of hierarchical levels of covariation among traits before drawing that parallel. While other workers have made similar points about how phylogenetic information can help refine hypotheses for the evolution of broad interspecific associations among traits (Carothers 1984; Maddison 1990 cited in Sillen-Tullberg 1988; Cooper 1995; McPeek 1995), we ask whether micro-evolutionary maintenance processes can be used to infer the origin of macro-evolutionary patterns within a group. The question is an appropriate one for many classes of characters, but we feel it particularly important when behavioural traits are involved because of the interest in the way in which behavioural variation can drive the evolution of other types of traits (Wcislo 1989; West-Eberhardt 1989; Basolo 1995). Additionally, results from intraspecific studies of behavioural variation have been used to interpret broad interspecific corre-lations (e.g. Basolo 1990; Losos 1990; Emerson 1991; Reynolds et al. 1993; Morris & Ryan 1996). We use poeciliid fish as our example. In particular, we examine the positive association between body size-adjusted gonopodium length and reliance on forced insemination. The gonopodium is the modified anal fin used by males of all poeciliid species to place spermato-phores on or within the female's genital opening for internal fertilization. We ask whether it is reasonable to interpret the current selective forces maintaining this correlation among individuals within a population as reflective of the historical selective pressures that molded the interspecific association. All poeciliids observed to date perform a type of forced insemination attempt termed a gonopodial thrust. The male orients himself behind a female, brings the gono-podium to a forward position, and swims forward, attempting to insert the gonopodial tip into the female's gonopore. This behaviour has no signal function, and there are no countersignals directed from the female towards the male. Farr (1989) contends that this behav-iour cannot be considered a form of display. A second behaviour, termed a courtship display, is exhibited by a subset of poeciliid species. All poeciliid courtship displays are visual and involve a combination of stereotyped swimming motions and fin postures performed by males towards females in an attempt to elicit female cooper-ation in mating (Farr 1989). Rosen & Tucker (1961) note that in poeciliid species that show courtship display behaviours, stereotyped male courtship displays and female acceptance postures precede copulation. Most or all species that show courtship display behaviours also show frequent gonopodial thrusting. The fundamental observation of the interspecific pat-tern was made by Rosen & Tucker (1961) in their analysis of behavioural and morphological variation in several poeciliid species. They suggested that there was a negative association between male courtship display behaviour and relative length of the gonopodium (gonopodium length adjusted for variation in male body size). They found that, of the taxa they studied, those with long gonopodia (gonopodial length greater than one-third of body length) did not incorporate courtship display behaviour, or mouth or body contact during precopu-latory interactions. Those taxa with short gonopodia (gonopodium less than one-third of body length) did perform courtship displays and made mouth or body contact. Their explanation for this pattern was predicated on the assumption that a long gonopodium was the plesiomorphic condition. While Rosen & Tucker offered no hypothesis for the origin of the short gonopodium, they suggested that courtship displays and less reliance on gonopodial thrusts evolved to increase the effective-ness of the short gonopodium that was already present in certain genera such as Gambusia and Poecilia. In particu-lar, the need to properly position the shortened gono-podium drove the evolutionary modification of pectoral and pelvic fins in males for greater manoeuvrability (see also Hubbs & Reynolds 1957; Peden 1972); courtship displays evolved to elicit female cooperation so that males could obtain the relatively longer time needed for Correspondence: M.
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Identifying sex of hatchling turtles is difficult because juveniles are not obviously externally dimorphic, and current techniques to identify sex are often logistically unfeasible for field studies. We demonstrate a widely applicable and inexpensive alternative to detect subtle but significant sexual dimorphism in hatchlings, using landmark-based geometric morphometric methods. With this approach, carapace landmarks were digitized from photographs of each hatchling, and shape variables were generated after variation in size, location and orientation were eliminated. These variables were then analyzed for sexual dimorphism, and used in discriminant function analysis to estimate sex of each hatchling. Using this approach on two species (Chrysemys picta and Podocnemis expansa), we found this method had high accuracy in assigning sex when compared with true sex (98% and 90%, respectively), and cross-validation revealed a correct classification rate of 85%. These correct classification rates were considerably higher than those found on the same species using linear distance measurements as data. We also explored two alternative statis- tical approaches for assessing sex (K-means clustering and multiple logistic regres- sion) and found that these alternative approaches were accurate only 61% and 78% of the time, respectively, in C. picta and 69% and 77% of the time in P. expansa. These findings are similar to classification rates found for turtle species using ap- proaches based on linear distance measurements. We also found that the observed sexual dimorphism differed between the two species. In P. expansa, males displayed relatively more expansion of the central region of the carapace relative to females, whereas in C. picta this pattern was reversed. We conclude that discriminant analysis of morphology quantified using geometric morphometrics provides researchers with a powerful tool to discriminate between male and female hatchling turtles.
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This study documents four wild-caught, interspecific hybrids between sailfin mollies (Poecilia velifera or P. petenensis) and shortfin mollies (P. mexicana or P. orri) from the Yucatán peninsula and Isthmus of Tehuantepec regions of México. In canonical discriminant analysis of morphological data all four putative hybrid males were intermediate in shape between shortfin and sailfin molly species, falling well outside 95% confidence ellipses for those putative parental species. For two of the four hybrid individuals, we used allele size differences at the nuclear Xsrc gene between sailfin and shortfin species to determine that one was a first (F1) or early generation (F2, BC1) hybrid and the other was a later generation (>F1) hybrid. Sequences of the mtDNA control region (483 bp) and Xsrc nuclear gene (636 bp) indicated that the female parent of the early generation hybrid individual was P. mexicana and the male parent was P. velifera. Thus, while rare in the wild, interspecific hybridization and introgression between sailfin and shortfin mollies does occasionally occur despite the existence of behavioral pre-mating isolating mechanisms.
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The analysis of shape is a fundamental part of much biological research. As the field of statistics developed, so have the sophistication of the analysis of these types of data. This lead to multivariate morphometrics in which suites of measurements were analyzed together using canonical variates analysis, principal components analysis, and related methods. In the 1980s, a fundamental change began in the nature of the data gathered and analyzed. This change focused on the coordinates of landmarks and the geometric information about their relative positions. As a by‐product of such an approach, results of multivariate analyses could be visualized as configurations of landmarks back in the original space of the organism rather than only as statistical scatter plots. This new approach, called “geometric morphometrics”;, had benefits that lead Rohlf and Marcus (1993) to proclaim a “revolution”; in morphometrics. In this paper, we briefly update the discussion in that paper and summarize the advances in the ten years since the paper by Rohlf and Marcus. We also speculate on future directions in morphometric analysis.
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A 505-bp sequence from the control region (D-loop) and the complete 1047 bp of the NADH dehydrogenase subunit 2 (ND2) gene were examined for individuals from 11 species of mollies included in the group Mollienesia. All three species of sailfin mollies of the Poecilia latipinna species complex were included (P. latipinna, P. petenensis and P. velifera); this group is named after the strikingly large dorsal fin in males. Six members of the shortfin P. mexicana complex (P. gilli, P. mexicana, P. orri, P. catemaconis, P. latipunctata and P. sulphuraria) and two members of the shortfin P. sphenops complex (P. butleri and P. sphenops) were examined. To test the monophyly of the Molliensia group, two species of mollies outside of this group were included: P. caucana and P. vivipara. The guppy P. reticulata was used as the outgroup taxon. Similar topologies were recovered using three phylogenetic methods (maximum parsimony, neighbour joining and maximum likelihood) and revealed several interesting relationships. First, all members of Mollienesia form a monophyletic group, which supports the more traditional taxonomy and classification of these species as comprising the subgenus Mollienesia as proposed previously. Second, the species of mollies outside of the Mollienesia group are only loosely allied with the Mollienesia clade; P. caucana is the sister taxon to Mollienesia, but P. vivipara lies outside of this Mollienesia-P. caucana clade. Third, the three sailfin molly species form a monophyletic group within the Mollienesia clade, but interestingly, shortfin species are paraphyletic due to the inclusion of a single shortfin species, P. latipunctata, within this sailfin clade. The exact placement of P. latipunctata within the sailfin clade is unclear. Fourth, the remaining shortfin species form a monophyletic sister clade to the sailfins and are separated into two groups, one containing P. sphenops and P. catemaconis and a second lineage leading to the remaining shortfin species. This arrangement does not support the morphological separation of shortfins into a P. sphenops and a P. mexicana species complex. Bootstrap analyses support the monophyly of Mollienesia (78–85%), the sailfin clade (100%) and the shortfin clade (79–95%).
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Threespine sticklebacks, small fish with a circumglobal distribution in coastal marine and freshwater of the northern hemisphere, present a remarkable scope of variation in body and fin shape among populations. The repeated evolution of divergent body shapes in a radiation of stickleback from Cook Inlet, Alaska suggests that diversification has proceeded by extensive parallel selection. To explore this hypothesis, hydromechanical equations of fish propulsion and descriptions of stickleback foraging and anti-predator behaviours were used to develop a series of hypotheses that predicted the evolutionary effects of native predatory fishes (NPF) and relative littoral area (RLA) on body shape. Body shape was measured using Cartesian coordinates of anatomical landmarks transformed by the generalized resistant fit super-imposition. In general, the results were consistent with the hypotheses that (1) RLA has a direct effect on selection for foraging behaviour and morphology, (2) RLA has an indirect effect on selection for morphology employed in predator evasion, (3) presence of NPF has a direct effect on selection for evasive morphology, and (4) presence of NPF has an indirect effect on selection for foraging behaviour and morphology. The magnitude of the divergence of body shapes present in the Cook Inlet system suggests that extreme phenotypes have evolved by opportunistic expansion into new habitat relatively free of interspecific competition.
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Body shape is a difficult, but important, trait to quantify. Researchers have traditionally used multivariate analysis of several linear measures ('trusses') across the body form to quantify shape. Newer geometric morphometric methods claim to better estimate shape because they analyze the geometry among the locations of all landmarks simultaneously rather than the linear distances between pairs of landmarks. We tested this claim by comparing the results of several traditional morphometric analyses against a newer geometric analysis involving thin-plate splines (TPS), all applied to a common data set of morphologically variable new world cichlids Amphilophus citrinellus and A. zaliosus. The TPS method yielded slightly stronger evidence of morphological differences among forms, although traditional methods also distinguished the two species. Perhaps our most important result was the idiosyncratic interpretation of shape variation among the traditional truss-based methods, whereas the generation of deformation grids using the TPS approach yielded clear and visually interpretable figures. Our results indicate that geometric morphometrics can be a more effective way to analyze and interpret body form, but also that traditional methods can be relied upon to provide statistical evidence of shape differences, although not necessarily accurate information about the nature of variation in shape.
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Under laboratory conditions, female guppies demonstrate a clear preference for males with larger tails, and this preference translates into enhanced reproductive fitness for these males. Females also prefer males with higher display rates, a behavior which appears to be linked to tail size, but which can be experimentally disassociated. This appears to be a case of female-choice sexual selection.
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We integrate experimental studies attempting to duplicate all or part of the speciation process under controlled laboratory conditions and ask what general conclusions can be made concerning the major models of speciation. Strong support is found for the evolution of reproductive isolation via pleiotropy and/or genetic hitchhiking with or without allopatry. Little or no support is found for the bottleneck and reinforcement models of speciation. We conclude that the role of geographical separation in generating allopatry (i.e., zero gene flow induced by spatial isolation) has been overemphasized in the past, whereas its role in generating diminished gene flow in combination with strong, discontinuous, and multifarious divergent selection, has been largely unappreciated.
Article
We present results of an experiment designed to address fundamental issues in the ecology and evolution of plastic trophic morphology: (1) Is observed plasticity adaptive? (2) How much interspecific morphological variation is the result of plasticity? (3) Have different selective regimes resulted in the evolution of different degrees of plasticity? (4) Is genetic variation for phenotypic plasticity present in contemporary populations? We raised fish from two recently diverged species of freshwater threespine sticklebacks on two different diets representative of the natural prey of the two species. Both species exhibited morphological plasticity in an adaptive direction: each species more closely resembled the other when raised on the latter's diet. Dietreversal reduced the natural morphological gap between these two species, -1% to 58%, depending on the trait. One species is known to have a more variable diet in the wild than the other species, and we found that it also exhibited the greater amount of morphological plasticity. Given that the two species have recently diverged, this result is compelling evidence that diet variability is important in the evolution of plastic trophic morphology. Finally, by using a full-sib experimental design, we demonstrated that genetic variation for morphological plasticity exists in contemporary populations, thus confirming that plasticity has evolutionary potential.
Article
The ecological hypothesis of speciation is that reproductive isolation evolves ultimately as a consequence of divergent natural selection on traits between environments. Ecological speciation is general and might occur in allopatry or sympatry, involve many agents of natural selection, and result from a combination of adaptive processes. The main difficulty of the ecological hypothesis has been the scarcity of examples from nature, but several potential cases have recently emerged. I review the mechanisms that give rise to new species by divergent selection, compare ecological speciation with its alternatives, summarize recent tests in nature, and highlight areas requiring research.
Article
Fast-start performance of eight groups of rainbow trout with various fin-rays removed was measured to test the hydromechanical theory (Weihs, 1973) that large fins are required for acceleration. A trend towards decreasing performance was found for the following sequence of fin-ray amputations: control (pelvic rays amputated); dorsal fin; anal fin; dorsal lobe of caudal fin and ventral lobe of caudal fin; ventral lobe of caudal fin and anal fin; dorsal and ventral lobes of caudal fin; both caudal-fin lobes and anal fin. The series represents progressive reduction in fin and body area, as well as reduction in these areas where lateral movements are largest. Effects of fin amputation on performance were statistically significant (P > 0·05) in comparison with controls only for the last three groups lacking the caudal fin. The results confirm the hydromechanical theory, and lead to the conclusion that mechanically optimum lateral body profiles for faststart and for steady (cruising and sprint) performance are mutually exclusive. This mechanical restriction can be circumvented only in bony fish, with the evolution of flexible, collapsible fins that permit major variation in lateral body profile.
Article
We examined both female and male mate choice in the sailfin molly, Poecilia latipinna. Female mollies preferred larger males over smaller ones when comparing males from their own populations. Although the expression of this preference depends on a female's receptive state, the level of female preference does not appear to be associated with any other attribute of the female or of the males. When presented with males of the same size from different populations, females preferred native over foreign males in some but not all population combinations. These results cannot be explained by a bias for higher size-specific rates of courtship displays that is shared by all females. Males preferred larger over smaller females; larger males exhibited stronger preferences, and preference for the larger female also increased as the disparity in size between the two object females increased. We found no evidence that males preferred native over foreign females when encountered singly or in size-matched combinations. These results indicate that discrimination among populations arises because females exercise divergent directional preferences for size-specific trait values that are associated with differences among males in these values. This result implies an active role for sexual selection in contributing to the maintenance of the behavioral or morphological distinctions among males observed within and among populations.
Article
New methods for allometry are presented. The definition of random size and shape variables which are visually meaningful is stressed. In contrast to classical methods which attempt to summarize size-shape associations with single coefficients, the methods here permit the study of the entire joint distribution of size and shape variables. The diversity of allometric hypotheses is revealed, and the choice of size variable is shown to be important. Under a multivariate lognormal assumption, exact statistical tests are presented. The methods are illustrated by study of geographic variation in the red-winged blackbird in Florida. Bill depth and bill shape, but not bill length, show interesting covariation across Florida. The observed bill variation for the red-winged blackbird is suggestive of variation found across species of Darwin's finches, and is also consistent with size trends observed in a variety of bird species in eastern North America.
Article
Females of a species can influence the variance in male reproductive success without exercising an active choice of males by inciting males to increase their levels of competition for mates. We examined whether males of the live-bearing sailfin mollie, Poecilia latipinna, were able to recognize when females were carrying fertilizable ova. Males dramatically increased their rates of sexual behavior toward females immediately after they gave birth. Males also displayed higher rates of sexual behavior toward virgin females than toward gravid females. Fertility advertisement by females allows intermale competition to be focused on a few individual females at any one time. This focus appears to provide a reproductive advantage to larger male mollies and is thus an important element influencing the outcome of sexual selection. We suggest that fertility advertisement by females may play a similarly important role in other poeciliids.
Article
An official journal of the Genetics Society, Heredity publishes high-quality articles describing original research and theoretical insights in all areas of genetics. Research papers are complimented by News & Commentary articles and reviews, keeping researchers and students abreast of hot topics in the field.
Article
Twenty-two percent of all allozyme variation documented in the sailfin molly (Poecilia latipinna) was attributable to regional differences, while only 3% was attributable to differences among demes within regions. Of the variation documented in a given region, 6-12% was attributable to variation among demes. Cluster analyses supported these conclusions quantitatively. Spatial-autocorrelation analyses offered more explicit support: demes separated by increasingly greater distances were increasingly dissimilar. Analyses using F statistics and rare alleles suggest "effective gene flow rates" (the product of effective population size and gene flow rate) of approximately 4, a level more than sufficient to prevent local independence of gene-frequency dynamics. These results, taken together, suggest that mollies do not have a population structure conducive to the operation of Wright's shifting-balance process and make the striking patterns of interdemic variation in body size and sexual behavior observed in this species all the more interesting.
Book
The book presents the continental fishes of Quintana Roo, Caribbean versant of Yucatan Peninsula. It includes identification keys and synopses with nomenclature, common names, morphology, biogegoraphy, ecology and conservation status. Color photographs and distribution maps are also included. NOTE: this pdf is not the final published version. Among the errata in this pdf, Rocio gemmata is referred to as "aff. friedrichsthalii".
Article
Male sailfin mollies show size-dependent variation in sexual behaviour. The level of variation between six north Florida populations in rates of condition-dependent behaviours was estimated and whether behavioural variation is ordered with respect to male body size distributions was determined. In five of six populations, courtship display rates increased with male length, supporting previous evidence. Several results were not consistent with those reported elsewhere. Rates of gonopodial thrusting and gonoporal nibbling were not related to male body length. Courtship display rates adjusted for male body size were not ordered with respect to male body size distributions. High adjusted courtship rates were characteristic of populations where males were predominantly large and where they were predominantly small. No consistent pattern of variation existed between populations in the relationships of the three behaviour patterns to one another. Variation between populations in size-dependent behaviour is therefore far more extensive but less patterned than previously reported. These results imply that evolution can adjust the rates of the three behaviour patterns both independently of one another and of body size, and that the direction of behavioural evolution is not likely to be constrained by covariances within any single natural population.
Article
The interosseal and suspensory ligaments of the axial and appendicular skeleton of the Western Mosquitofish, Gambusia affinis affinis were investigated in whole-mounted late embryonic and adult female and male G. a. affinis stained with alcian blue and alizarin red S, cleared, and viewed using differential interference contrast. The interosseal and suspensory ligaments of late embryonic female G. a. affinis are reduced prior to sexual differentiation and continue reduced in adult females. However, in late embryonic male G. a. affinis the interosseal and suspensory ligaments are well developed prior to sexual differentiation and become robust in adult males. Treating late embryonic female G. a. affinis with either 30.0 or 40.0 μg/ diet of 17α-methyltestosterone led to the premature calcification of the hemal spine of the 13th vertebra. Treating late embryonic female G. a. affinis with 17α-methyltestosterone did not lead to the remodeling of the hemal spines of the 14th–16th vertebrae. Thus, in all female G. a. affinis treated with 17α-methyltestosterone, no anterior transposition of the anal fin and its appendicular support was observed. However, treating late embryonic male G. a. affinis with 30.0 μg/g diet of 17α-methyltestosterone led to the premature calcification of the hemal spine of the 13th vertebra, blocking the anterior transposition in only 62.5% of the males treated, and treating late embryonic male G. a. affinis with 40.0 μg/g diet of 17α-methyltestosterone led to the premature calcification of the hemal spine of the 13th vertebra, blocking the anterior transposition in all (100.0%) males treated. Treatment with either 30.0 or 40.0 μg/g diet of 17α-methyltestosterone appeared not to completely effect the interosseal and suspensory ligaments of late embryonic male G.a. affinis as evident by the male-specific remodeling of the hemal spines of the 14th–16th vertebrae. The results of this study implicate the interosseal and suspensory ligaments in the male-specific remodeling of the axial and appendicular skeletal elements. Following the resorption of the 13th hemal spine, the interosseal and suspensory ligaments in late embryonic male G. a. affinis develop enough tension to cause directional growth, bending, and elongation of the 14th–16th hemal spines, thus providing a mechanism for the anterior transposition of the sexually dimorphic anal fin and its appendicular support. The data also support the need to revise the interosseal and suspensory ligament nomenclature by assigning the designation of ‘female’ and ‘male’ to these ligaments.
Article
Morphometrics is the statistical study of biological shape and shape change. Its richest data are landmarks, points, such as the bridge of the nose, that have biological names as well as geometric locations. This book is the first systematic survey of morphometric methods for landmark data.
Article
Microhabitat use and body morphology were compared among 15 warmwater stream fishes from the Alabama River (Alabama, U.S.A.) watershed. Morphological variation among separate populations of a species was detected in 14 of the 15 species, indicating that populations should be separated in analyses among species. Comparison of morphological variation between microhabitat generalist and specialist species suggested that all species may vary in morphology relative to their environment. Regression analysis showed that within two families, Cyprinidae and Percidae, morphology was related to specific microhabitat variables. In the Centrarchidae, morphology was not related to any microhabitat variables. Morphological differences among the species occurred along gradients that were similar to gradients of habitat utilization, indicating that within a family, species widely separated in microhabitat use were morphologically different and species using similar microhabitats were similar in morphology. Our results suggest that patterns of morphological variation correspond to properties of the available habitat for warmwater stream fish species.
Article
[1) Auf Grund von Größe und Differenzierungsgeschwindigkeit wird bei M. velifera und M. latipinna zwischen Früh- und Spät-♂ ♂ unterschieden. Die Spät-♂ ♂ von M. velifera bilden eine Dorsale aus, die meist höher als der Körper ist. Auf einige Faktoren für die Ausbildung der hohen Dorsale wird eingegangen. Die ♂♂ des zur Verfügung stehenden Stammes von M. latipinna bildeten dagegen keine hohe Dorsale aus2) Alle ♂♂ der beiden
Article
We tested the mating preference of female sailfin mollies (Poecilia latipinna) by presenting them with pairs of dummy males differing in: (I) sailfin and body size together (holding sailfin : body size ratio constant); (II) body size alone (holding sailfin size constant); (III) sailfin size alone (holding body size constant); and (IV) sailfin : body size ratio (holding total lateral projection area constant). Females spent more time near dummies of greater sailfin or greater body size. The preference functions based on the first three sets of stimuli showed a similar pattern: the preference between any two simultaneously presented dummies increased with the magnitude of the discrepancy in lateral projection area (LPA) between them. However, when LPA was held constant in expt (IV), neither body size, sailfin size, nor any particular dummy (i.e. any particular sailfin + body size combination) was preferred. These findings suggest that increased LPA is more stimulating to sexually receptive females and that females consequently prefer larger males. The sailfin may therefore have evolved as a way for males to exploit this sensory bias and appear larger to prospective mates.
Article
Geometric shape analyses were used to study body shape and size variation among populations of the livebearing fish Poecilia vivipara inhabiting the recently formed coastal lagoons of Grussaí and Iquipari in Northern Rio de Janeiro State, Brazil. The largest components of morphological variation among females were between different habitats in the same lagoon, whereas for males there were larger differences between lagoons than between habitats. The shape differences were mostly localized in the head region and midbody, which indicated different patterns of locomotion and foraging behaviour optimized for the habitat experienced by each population. The pattern of size variation was similar to that of size-independent shape variation.
Article
Variation in ontogeny can produce phenotypic variation both within and among species. I investigated whether changes in timing and rate of growth were a source of phenotypic variation in a putative incipient species group of pupfish (Cyprinodon spp.). On San Salvador Island, Bahamas, sympatric forms of pupfish differ in morphology but show only partial reproductive isolation in the laboratory. Offspring from two forms and two geographical areas and their hybrids were bred in the laboratory, and ontogenetic trajectories of their feeding morphology were followed until maturity. In the Bahamian pupfish the two forms grow along similar size but not shape trajectories. Two heterochronic parameters, onset and rate of growth, alter shape trajectories in the Bahamian pupfish. Similar forms from different geographical areas (Florida and the Bahamas) grow along parallel shape trajectories, differing only in one heterochronic parameter, the onset shape. Hybrids within and between the pupfish forms produced intermediate feeding morphologies that were influenced by their maternal phenotype, suggesting that maternal effects may be a source of phenotypic variation in shape that can persist to maturity. In Cyprinodon, small changes in multiple heterochronic parameters translate into large phenotypic differences in feeding morphology.
Article
We examined intraspecific morphological diversification between river channel and lagoon habitats for two Neotropical fish (Bryconops caudomaculatus, Characidae; Biotodoma wavrini, Cichlidae). We hypothesized that differences between habitats (e.g. flow regime, foraging opportunities) might create selective pressures resulting in morphological divergence between conspecific populations. We collected fish from four channel-lagoon habitat pairs in the Río Cinaruco, Venezuela, and compared body morphology using geometric morphometrics. There were two aspects of divergence in both species: (1) placement of maximum body depth and (2) orientation of the mouth. For both species, maximum body depth was positioned more anteriorly (i.e. fusiform) in the river channel than in lagoons. Both species exhibited a relatively terminal mouth in lagoons compared to the channel. The mouth of B. caudomaculatus was relatively upturned, whereas the mouth of B. wavrini was relatively subterminal, in channel habitats. Observed morphological patterns are consistent with functional morphological principles suggesting adaptive divergence. We also show that spatial distance between habitats, presumably reflecting rates of population mixing, appears to have constrained diversification. For both species, morphological divergence increased with distance between habitats. Thus morphological divergence between channel and lagoon habitats apparently reflects a balance between diversification driven by natural selection, and homogenization driven by population mixing. © 2003 The Linnean Society of London, Biological Journal of the Linnean Society, 2003, 80, 689–698.
Article
Scalation, colour pattern, linear and geometric morphometrics were used to quantify geographical differentiation in the long-nosed snake, Rhinocheilus lecontei, and to test the hypothesis that all four subspecies are morphologically distinct. Also investigated were potential associations between morphological (scalation, colour pattern, linear measurements) and environmental variables (climate, vegetation, soil). Sexual dimorphism was weakest for geometric and strongest for linear morphometric variables. Morphological variables differed widely in their ability to differentiate subspecies. Linear morphometric variables achieved the most statistically significant pairwise Mahalanobis distances between subspecies, while geometric morphometrics largely failed to differentiate them. Colour pattern showed the strongest and linear morphometrics the weakest correlation with environment. Several characters varied continuously along latitudinal or longitudinal gradients, such that, in some cases, the clines for closely related traits were discordant. No one subspecies was consistently divergent in all analyses, leading to the conclusion that the three mainland subspecies are not sufficiently distinct to warrant separate subspecies status. The island subspecies, though not always statistically distinct, is geographically separate from other populations and differs in characters related to size. Given the small number of specimens available, a decision regarding its taxonomic status (i.e. elevation to species level) is best deferred until additional specimens can be examined and data on molecular variation can be analysed. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society, 2004, 83, 65–85.
Article
Three populations (one from a river and two from lakes) of Salaria fluviatilis, the only exclusively freshwater representative of the Blenniidae, showed significant differences in reproductive behaviour and morphology. Breeding males and females were significantly larger at maturity in the river than the two lake populations. The two lake populations, however, showed the greatest degree of morphological difference, the river population being intermediate. The mating system of each population could be described as resource-based and promiscuous with parasitic ‘sneaker’ males that released sperm in the nests of other males. During spawning, males from the river population released sperm significantly more often than the lake populations. This was paralleled by a greater investment in sperm as measured by relative testis mass in the river population. This was interpreted as the need to counteract the loss of sperm during fertilization as a result of the strong flow in the river. Thus some of the patterns of trait variance fitted predictions of adaptations. Other traits, however, varied randomly across populations suggesting change through genetic drift.