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We describe the histological characteristics of the testis and spermatogenesis of the cave molly Poecilia mexicana, a viviparous teleost inhabiting a sulfur spring cave, Cueva del Azufre, in Tabasco, Southern Mexico. P. mexicana has elongate spermatogonial restricted testes with spermatogonia arranged in the testicular periphery. Germ cell development occurs within spermatocysts. As spermatogenesis proceeds, the spermatocysts move longitudinally from the periphery of the testis to the efferent duct system, where mature spermatozoa are released. The efferent duct system consists of short efferent duct branches connected to a main efferent duct, opened into the genital pore. Spermatogenesis consisted of the following stages: spermatogonia (A and B), spermatocytes (primary and secondary), spermatids, and spermatozoa. The spermatozoa are situated within spermatocysts, with their heads oriented toward the periphery and flagella toward the center. Once in the efferent duct system, mature spermatozoa are packaged as unencapsulated sperm bundles, that is, spermatozeugmata. We suggest that the histological characteristics of the testis and spermatogenesis of P. mexicana from the Cueva del Azufre, and the viviparous condition where the spermatozoa enter in the female without been in the water, have allowed them to invade sulfurous and/or subterranean environments in Southern Mexico, without requiring complex morphofunctional changes in the testis or the spermatogenetic process.

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The structure of the ovary and oogenesis of Poecilia mexicana from an active sulfur spring cave is documented. Poecilia mexicana is the only poeciliid adapted to a subterranean environment with high hydrogen sulfide levels and extreme hypoxic conditions. Twenty females were captured throughout one year at Cueva del Azufre, located in the State of Tabasco in Southern Mexico. Ovaries were processed with histological techniques. P. mexicana has a single, ovoid ovary with ovigerous lamella that project to the ovarian lumen. The ovarian wall presents abundant loose connective tissue, numerous melanomacrophage centers and large blood vessels, possibly associated with hypoxic conditions. The germinal epithelium bordering the ovarian lumen contains somatic and germ cells forming cell nests projecting into the stroma. P. mexicana stores sperm in ovarian folds associated with follicles at different developmental phases. Oogenesis in P. mexicana consisted of the following stages: (i) oogonial proliferation, (ii) chromatin nucleolus, (iii) primary growth, subdivided into: (a) one nucleolus, (b) multiple nucleoli, (c) droplet oils-cortical alveoli steps; (iv) secondary growth, subdivided in: (a) early secondary growth, (b) late secondary growth, and (c) full grown. Follicular atresia was present in all stages of follicular development; it was characterized by oocyte degeneration, where follicle cells hypertrophy and differentiate in phagocytes. The ovary and oogenesis are similar to these seen in other poeciliids, but we found frequent atretic follicles, melanomacrophage centers, reduced fecundity and increased of offspring size.

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Large size of individual offspring is routinely selected for in highly competitive environments, such as in low-predation populations of the Trinidadian guppy (Poecilia reticulata). Large guppy offspring outcompete their smaller conspecifics, but the functional mechanisms underlying this advantage are unknown. We measured jaw kinematics during benthic feeding and cranial musculoskeletal morphologies in neonates and juveniles from five populations of Trinidadian guppy and found that both kinematics and morphologies vary substantially with neonatal size. Rotation at the intramandibular joint (IMJ), but not the quadratomandibular joint (QMJ), increases with size among guppy offspring, from 11.7° in the smallest neonates to 22.9° in the largest neonates. Ossification of the cranial skeleton varies from 20% in the smallest neonates to 90% in the largest. Relative to standard length (SL; jaw tip to caudal fin base distance), the surface area of jaw-closing musculature scales with positive allometry (SL2.72) indicating that muscle growth outpaces body growth. Maximum gape also scales with positive allometry (SL1.20), indicating that larger neonates are capable of greater jaw excursions. These findings indicate that size is not the sole adaptive benefit to producing larger offspring; maturation provides a potential functional mechanism underlying the competitive advantage of large offspring size among Trinidadian guppies.

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Assortative mating is critical for reproductive isolation during speciation; however, the mechanisms underlying mating preferences are often unknown. Assortative mating can be mediated through preferences for condition-dependent and adaptive ("magic") traits, but rigorously testing these hypotheses has been impeded by trait covariation in living organisms. We used computer-generated models to examine the role of body shape in producing association preferences between fish populations undergoing ecological speciation in different habitat types. We demonstrate that body shape can serve as an adaptive trait (variation in head size between populations) and a condition-dependent signal (variation in abdominal distention among individuals). Female preferences for stimuli varying in only one aspect of body shape uncovered evidence for body shape as a magic trait across population pairs, but no evidence for body shape serving as a condition-dependent signal. Evolution of preferences only in females from one habitat type as well as stronger preferences in sympatric nonsulfidic as opposed to allopatric nonsulfidic populations suggests that reinforcement may have played a role in producing the observed patterns.

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Colour polymorphism is a recurrent feature of natural populations, and its maintenance has been studied in a range of taxa in their native ranges. However, less is known about whether (and how) colour polymorphism is maintained when populations are removed from their native environments, as in the case of introduced species. We here address this issue by analyzing variation in colour patterns in recently-discovered introduced populations of the guppy (Poecilia reticulata) in Panama. Specifically, we use classic colour analysis to estimate variation in the number and the relative area of different colour spots across low predation sites in the introduced Panamanian range of the species. We then compare this variation to that found in the native range of the species under low- and high predation regimes. We found aspects of the colour pattern that were both consistent and inconsistent with the classical paradigm of colour evolution in guppies. On one hand, the same colours that dominated in native populations (orange, iridescent and black) were also the most dominant in the introduced populations in Panama. On the other, there were no clear differences between either introduced-low and native low- and high predation populations. Our results are therefore only partially consistent with the traditional role of female preference in the absence of predators, and suggest that additional factors could influence colour patterns when populations are removed from their native environments. Future research on the interaction between female preference and environmental variability (e.g. multifarious selection), could help understand adaptive variation in this widely-introduced species, and the contexts under which variation in adaptive traits parallels (or not) variation in the native range.

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Aunque la temperatura tiene grandes repercusiones en la biología de los peces, se desconocen los rangos de tolerancia térmica de la mayoría de los peces dulceacuícolas. Esta falta de información impide pronosticar respuestas al cambio climático y limita los análisis comparativos que podrían enriquecer estudios evolutivos y biogeográficos. Utilizamos la metodología del crítico térmico para cuantificar la capacidad de aclimatación y la tolerancia térmica en la especie neotropical dulceacuícola Poecilia caucana. Para peces aclimatados a 20C, 25ºC y 28ºC, los críticos térmicos mínimos (CTmin) fueron 12,52 ± 0,62ºC, 13,41 ± 0,56ºC y 14,24 ± 0,43ºC, respectivamente, y los críticos térmicos máximos (CTmax) fueron 38,43 ± 0,64ºC, 40,28 ± 0,92ºC y 41,57 ± 0,27ºC, respectivamente. Tanto el CTmin como el CTmax cambiaron significativamente con las temperaturas de aclimatación, indicando que P. caucana es efectivamente aclimatable. Comparada con otras especies de peces dulceacuícolas, la capacidad de aclimatación de P. cuacana fue baja para CTmin y promedio para CTmax. Estos resultados, en conjunto con los datos de otras especies, pueden ser utilizados para responder preguntas ecológicas y evolutivas más generales.

Although temperature has far-reaching effects on fish biology, the thermal tolerance ranges of most freshwater fish species are unknown. This lack of information precludes forecasting responses to climatic change and does not allow for comparative analyses that may inform evolutionary and biogeographic studies. We used the critical thermal methodology to quantify acclimation capacity and thermal tolerance in the Neotropical freshwater species Poecilia caucana . For fish acclimated to 20C, 25ºC, and 28ºC, critical thermal minima (CTmin) were 12.52 ± 0.62ºC, 13.41 ± 0.56ºC and 14.24 ± 0.43ºC respectively, and critical thermal maxima (CTmax) were 38.43 ± 0.64ºC, 40.28 ± 0.92ºC and 41.57 ± 0.27ºC, respectively. Both CTmin and CTmax changed with acclimation temperatures, indicating that P. caucana was effectively acclimatable. Relative to values reported for other freshwater fish species, the acclimation capacity of P. caucana for CTmin was low, but it was average for CTmax. The data, together with similar work in other species, can be used in analyses focusing on broad ecological and evolutionary questions.

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Aunque la temperatura tiene grandes repercusiones en la biología de los peces, se desconocen los rangos de tolerancia térmica de la mayoría de los peces dulceacuícolas. Esta falta de información impide pronosticar respuestas al cambio climático y limita los análisis comparativos que podrían enriquecer estudios evolutivos y biogeográficos. Utilizamos la metodología del crítico térmico para cuantificar la capacidad de aclimatación y la tolerancia térmica en la especie neotropical dulceacuícola Poecilia caucana. Para peces aclimatados a 20C, 25ºC y 28ºC, los críticos térmicos mínimos (CTmin) fueron 12,52 ± 0,62ºC, 13,41 ± 0,56ºC y 14,24 ± 0,43ºC, respectivamente, y los críticos térmicos máximos (CTmax) fueron 38,43 ± 0,64ºC, 40,28 ± 0,92ºC y 41,57 ± 0,27ºC, respectivamente. Tanto el CTmin como el CTmax cambiaron significativamente con las temperaturas de aclimatación, indicando que P. caucana es efectivamente aclimatable. Comparada con otras especies de peces dulceacuícolas, la capacidad de aclimatación de P. cuacana fue baja para CTmin y promedio para CTmax. Estos resultados, en conjunto con los datos de otras especies, pueden ser utilizados para responder preguntas ecológicas y evolutivas más generales.(AU)

Although temperature has far-reaching effects on fish biology, the thermal tolerance ranges of most freshwater fish species are unknown. This lack of information precludes forecasting responses to climatic change and does not allow for comparative analyses that may inform evolutionary and biogeographic studies. We used the critical thermal methodology to quantify acclimation capacity and thermal tolerance in the Neotropical freshwater species Poecilia caucana . For fish acclimated to 20C, 25ºC, and 28ºC, critical thermal minima (CTmin) were 12.52 ± 0.62ºC, 13.41 ± 0.56ºC and 14.24 ± 0.43ºC respectively, and critical thermal maxima (CTmax) were 38.43 ± 0.64ºC, 40.28 ± 0.92ºC and 41.57 ± 0.27ºC, respectively. Both CTmin and CTmax changed with acclimation temperatures, indicating that P. caucana was effectively acclimatable. Relative to values reported for other freshwater fish species, the acclimation capacity of P. caucana for CTmin was low, but it was average for CTmax. The data, together with similar work in other species, can be used in analyses focusing on broad ecological and evolutionary questions.(AU)

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Variation in energy availability or maintenance costs in extreme environments can exert selection for efficient energy use, and reductions in organismal energy demand can be achieved in two ways: reducing body mass or metabolic suppression. Whether long-term exposure to extreme environmental conditions drives adaptive shifts in body mass or metabolic rates remains an open question. We studied body size variation and variation in routine metabolic rates in locally adapted populations of extremophile fish (Poecilia mexicana) living in toxic, hydrogen sulfide-rich springs and caves. We quantified size distributions and routine metabolic rates in wild-caught individuals from four habitat types. Compared with ancestral populations in nonsulfidic surface habitats, extremophile populations were characterized by significant reductions in body size. Despite elevated metabolic rates in cave fish, the body size reduction precipitated in significantly reduced energy demands in all extremophile populations. Laboratory experiments on common garden-raised fish indicated that elevated routine metabolic rates in cave fish likely have a genetic basis. The results of this study indicate that adaptation to extreme environments directly impacts energy metabolism, with fish living in cave and sulfide spring environments expending less energy overall during routine metabolism.

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Morphological variations, according to the principles of ecomorphology, can be related to different aspects of the organism way of life, such as occupation of habitats and feeding behavior. The present study sought to examine the intraspecific variation in two populations of Poecilia reticulata Peters, 1859, that occur in two types of environments, a lotic (Maringá Stream) and a lentic (Jaboti Lake). Due to a marked sexual dimorphism, males and females were analyzed separately. Thus, the proposed hypotheses were that the populations that occur in distinct environments present morphological differences. The morphological variables were obtained using morphometric measurements and the ecomorphological indexes. The data were summarized in a Principal Component Analysis (PCA). A Multivariate Analysis of Variance (Manova) was made to verify significant differences in morphology between the populations. Males and females showed similar ecomorphological patterns according to the environment they occur. In general the population from Maringá Stream had fins with major areas, and the Jaboti Lake population eyes located more dorsally. Additionally, others morphological differences such as wider mouth of the males from Maringá Stream, wider heads on Jaboti Lake females and more protractible mouths on males from Jaboti Lake suggest a set of environmental variables that can possibly influence the ecomorphological patterns of the populations, as the water current, availability of food resources and predation. In summary, the initial hypotheses could be confirmed, evidencing the occurrence of distinct ecomorphotypes in the same species according to the environment type.(AU)

Variações morfológicas, de acordo com os princípios da ecomorfologia, podem ser relacionadas a diferentes aspectos do modo de vida dos organismos, como a ocupação de hábitats e comportamento alimentar. O presente estudo buscou analisar essas variações em nível intraespecífico em duas populações de Poecilia reticulata Peters, 1859, que ocorrem em dois tipos de ambientes, um lótico (ribeirão Maringá) e um lêntico (lago Jaboti). Por apresentar um acentuado dimorfismo sexual machos e fêmeas foram analisados separadamente. Assim, a hipótese proposta foi de que as populações, que ocorrem em ambientes distintos, possuem diferenças morfológicas. As variáveis morfológicas foram obtidas por meio de medidas morfométricas e índices ecomorfológicos. Os dados foram sumarizados em uma Análise de Componentes Principais. Também foi feita uma Análise de Variância Multivariada para verificar se existe diferença significativa na morfologia entre as populações. Machos e fêmeas mostraram padrões ecomorfológicos semelhantes de acordo com o ambiente em que ocorrem. No geral, a população do ribeirão Maringá apresentou nadadeiras com maiores áreas e a população do lago Jaboti apresentou olhos localizados em região mais dorsal. Adicionalmente, outras diferenças morfológicas como bocas mais largas nos machos do ribeirão Maringá, cabeças mais largas nas fêmeas do lago Jaboti e bocas mais protráteis nos machos do lago Jaboti, sugerem um conjunto de variáveis ambientais que possivelmente influenciam os padrões ecomorfológicos das populações, como, por exemplo, a corrente de água, disponibilidade de recursos alimentares e predação. Em síntese a hipótese inicial pode ser confirmada, evidenciando a ocorrência de ecomorfótipos distintos da mesma espécie de acordo com o tipo de ambiente.(AU)

Assuntos

RESUMO

Morphological variations, according to the principles of ecomorphology, can be related to different aspects of the organism way of life, such as occupation of habitats and feeding behavior. The present study sought to examine the intraspecific variation in two populations of Poecilia reticulata Peters, 1859, that occur in two types of environments, a lotic (Maringá Stream) and a lentic (Jaboti Lake). Due to a marked sexual dimorphism, males and females were analyzed separately. Thus, the proposed hypotheses were that the populations that occur in distinct environments present morphological differences. The morphological variables were obtained using morphometric measurements and the ecomorphological indexes. The data were summarized in a Principal Component Analysis (PCA). A Multivariate Analysis of Variance (Manova) was made to verify significant differences in morphology between the populations. Males and females showed similar ecomorphological patterns according to the environment they occur. In general the population from Maringá Stream had fins with major areas, and the Jaboti Lake population eyes located more dorsally. Additionally, others morphological differences such as wider mouth of the males from Maringá Stream, wider heads on Jaboti Lake females and more protractible mouths on males from Jaboti Lake suggest a set of environmental variables that can possibly influence the ecomorphological patterns of the populations, as the water current, availability of food resources and predation. In summary, the initial hypotheses could be confirmed, evidencing the occurrence of distinct ecomorphotypes in the same species according to the environment type.

Variações morfológicas, de acordo com os princípios da ecomorfologia, podem ser relacionadas a diferentes aspectos do modo de vida dos organismos, como a ocupação de hábitats e comportamento alimentar. O presente estudo buscou analisar essas variações em nível intraespecífico em duas populações de Poecilia reticulata Peters, 1859, que ocorrem em dois tipos de ambientes, um lótico (ribeirão Maringá) e um lêntico (lago Jaboti). Por apresentar um acentuado dimorfismo sexual machos e fêmeas foram analisados separadamente. Assim, a hipótese proposta foi de que as populações, que ocorrem em ambientes distintos, possuem diferenças morfológicas. As variáveis morfológicas foram obtidas por meio de medidas morfométricas e índices ecomorfológicos. Os dados foram sumarizados em uma Análise de Componentes Principais. Também foi feita uma Análise de Variância Multivariada para verificar se existe diferença significativa na morfologia entre as populações. Machos e fêmeas mostraram padrões ecomorfológicos semelhantes de acordo com o ambiente em que ocorrem. No geral, a população do ribeirão Maringá apresentou nadadeiras com maiores áreas e a população do lago Jaboti apresentou olhos localizados em região mais dorsal. Adicionalmente, outras diferenças morfológicas como bocas mais largas nos machos do ribeirão Maringá, cabeças mais largas nas fêmeas do lago Jaboti e bocas mais protráteis nos machos do lago Jaboti, sugerem um conjunto de variáveis ambientais que possivelmente influenciam os padrões ecomorfológicos das populações, como, por exemplo, a corrente de água, disponibilidade de recursos alimentares e predação. Em síntese a hipótese inicial pode ser confirmada, evidenciando a ocorrência de ecomorfótipos distintos da mesma espécie de acordo com o tipo de ambiente.

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Recently discovered male specimens of Phallotorynus pankalos are described and diagnosed from males of congener species on the basis of gonopodial morphology, color pattern and number of dorsal and anal-fin rays. The phylogenetic hypothesis of relationships among Phallotorynus species is reappraised with the inclusion of P. pankalos. Phallotorynus pankalos is hypothesized as sister to P. jucundus, a clade sister to P. victoriae or to a clade composed of P. dispilos and P. psittakos. Biogeography of Phallotorynus species is discussed, and it is suggested: (1) an early basal split between the rio Paraíba do Sul drainage and the Paraná-Paraguay system, separating P. fasciolatus from the ancestor of the remaining Phallotorynus species followed by a dispersal to rio Paraíba do Sul; (2) that the formation of the Sete Quedas falls may have isolated the ancestors of P. psittakos and P. dispilos. However, the sequence of events associated with the evolutionary history of Phallotorynus remains unclear and unsatisfactory.(AU)

Recentemente descobertos espécimes machos de Phallotorynus pankalos são descritos e diagnosticados dos machos de espécies congêneres com base na morfologia gonopodial, padrão de colorido e número de raios das nadadeiras dorsal e anal. A hipótese de relações filogenéticas entre as espécies de Phallotorynus foi reavaliada com a inclusão de P. pankalos. Phallotorynus pankalos é hipotetizado como irmão de P. jucundus, um clado irmão de P. victoriae ou a um clado composto por P. dispilos e P. psittakos. Biogeografia das espécies de Phallotorynus é discutida, e é sugerido: (1) uma separação basal entre as drenagens do rio Paraíba do Sul e o sistema Paraná-Paraguai, separando P. fasciolatus do ancestral dos demais Phallotorynus, seguida de uma dispersão para o rio Paraíba do Sul; (2) que a formação dos saltos das Sete Quedas podem ter isolado os ancestrais de P. psittakos e P. dispilos. No entanto, a sequência de eventos associados a história evolutiva de Phallotorynus continua obscura e insatisfatória.(AU)

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Recently discovered male specimens of Phallotorynus pankalos are described and diagnosed from males of congener species on the basis of gonopodial morphology, color pattern and number of dorsal and anal-fin rays. The phylogenetic hypothesis of relationships among Phallotorynus species is reappraised with the inclusion of P. pankalos. Phallotorynus pankalos is hypothesized as sister to P. jucundus, a clade sister to P. victoriae or to a clade composed of P. dispilos and P. psittakos. Biogeography of Phallotorynus species is discussed, and it is suggested: (1) an early basal split between the rio Paraíba do Sul drainage and the Paraná-Paraguay system, separating P. fasciolatus from the ancestor of the remaining Phallotorynus species followed by a dispersal to rio Paraíba do Sul; (2) that the formation of the Sete Quedas falls may have isolated the ancestors of P. psittakos and P. dispilos. However, the sequence of events associated with the evolutionary history of Phallotorynus remains unclear and unsatisfactory.

Recentemente descobertos espécimes machos de Phallotorynus pankalos são descritos e diagnosticados dos machos de espécies congêneres com base na morfologia gonopodial, padrão de colorido e número de raios das nadadeiras dorsal e anal. A hipótese de relações filogenéticas entre as espécies de Phallotorynus foi reavaliada com a inclusão de P. pankalos. Phallotorynus pankalos é hipotetizado como irmão de P. jucundus, um clado irmão de P. victoriae ou a um clado composto por P. dispilos e P. psittakos. Biogeografia das espécies de Phallotorynus é discutida, e é sugerido: (1) uma separação basal entre as drenagens do rio Paraíba do Sul e o sistema Paraná-Paraguai, separando P. fasciolatus do ancestral dos demais Phallotorynus, seguida de uma dispersão para o rio Paraíba do Sul; (2) que a formação dos saltos das Sete Quedas podem ter isolado os ancestrais de P. psittakos e P. dispilos. No entanto, a sequência de eventos associados a história evolutiva de Phallotorynus continua obscura e insatisfatória.

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BACKGROUND: Phenotypic diversity among populations may result from divergent natural selection acting directly on traits or via correlated responses to changes in other traits. One of the most frequent patterns of correlated response is the proportional change in the dimensions of anatomical traits associated with changes in growth or absolute size, known as allometry. Livebearing fishes subject to predation gradients have been shown to repeatedly evolve larger caudal peduncles and smaller cranial regions under high predation regimes. Poecilia vivipara is a livebearing fish commonly found in coastal lagoons in the north of the state of Rio de Janeiro, Brazil. Similar to what is observed in other predation gradients, lagoons inhabited by P. vivipara vary in the presence of piscivorous fishes; contrary to other poeciliid systems, populations of P. vivipara vary greatly in body size, which opens the possibility of strong allometric effects on shape variation. Here we investigated body shape diversification among six populations of P. vivipara along a predation gradient and its relationship with allometric trajectories within and among populations. RESULTS: We found substantial body size variation and correlated shape changes among populations. Multivariate regression analysis showed that size variation among populations accounted for 66% of shape variation in females and 38% in males, suggesting that size is the most important dimension underlying shape variation among populations of P. vivipara in this system. Changes in the relative sizes of the caudal peduncle and cranial regions were only partly in line with predictions from divergent natural selection associated with predation regime. CONCLUSIONS: Our results suggest the possibility that adaptive shape variation among populations has been partly constrained by allometry in P. vivipara. Processes governing body size changes are therefore important in the diversification of this species. We conclude that in species characterized by substantial among-population differences in body size, ignoring allometric effects when investigating divergent natural selection's role in phenotypic diversification might not be warranted.

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BACKGROUND: Geographic barriers to gene flow and divergence among populations in sexual traits are two important causes of genetic isolation which may lead to speciation. Genetic isolation may be facilitated if these two mechanisms act synergistically. The guppy from the Cumaná region (within the Cariaco drainage) of eastern Venezuela has been previously described as a case of incipient speciation driven by sexual selection, significantly differentiated in sexual colouration and body shape from the common guppy, Poecilia reticulata. The latter occurs widely in northern Venezuela, including the south-eastern side of Cordillera de la Costa, where it inhabits streams belonging to the San Juan drainage. Here, we present molecular and morphological analyses of differentiation among guppy populations in the Cariaco and San Juan drainages. Our analyses are based on a 953 bp long mtDNA fragment, a set of 15 microsatellites (519 fish from 20 populations), and four phenotypic traits. RESULTS: Both microsatellite and mtDNA data showed that guppies inhabiting the two drainages are characterised by a significant genetic differentiation, but a higher proportion of the genetic variance was distributed among populations within regions. Most guppies in the Cariaco drainage had mtDNA from a distinct lineage, but we also found evidence for widespread introgression of mtDNA from the San Juan drainage into the Cariaco drainage. Phenotypically, populations in the two regions differed significantly only in the number of black crescents. Phenotypic clustering did not support existence of two distinct groupings, but indicated a degree of distinctiveness of Central Cumaná (CC) population. However, CC population showed little differentiation at the neutral markers from the proximate populations within the Cariaco drainage. CONCLUSIONS: Our findings are consistent with only partial genetic isolation between the two geographic regions and indicate that the geographic barrier of Cordillera de la Costa has not played an important role in strengthening the incomplete pre-zygotic reproductive barrier between Cumaná and common guppy. Significant phenotypic differentiation between genetically similar (in terms of neutral variation) populations suggests that mate choice can maintain divergence at sexually selected traits despite gene flow. However, neither genetic nor phenotypic clustering supported delineation of two species within the region.

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Ecological speciation assumes reproductive isolation to be the product of ecologically based divergent selection. Beside natural selection, sexual selection via phenotype-assortative mating is thought to promote reproductive isolation. Using the neotropical fish Poecilia mexicana from a system that has been described to undergo incipient ecological speciation in adjacent, but ecologically divergent habitats characterized by the presence or absence of toxic H2S and darkness in cave habitats, we demonstrate a gradual change in male body colouration along the gradient of light/darkness, including a reduction of ornaments that are under both inter- and intrasexual selection in surface populations. In dichotomous choice tests using video-animated stimuli, we found surface females to prefer males from their own population over the cave phenotype. However, female cave fish, observed on site via infrared techniques, preferred to associate with surface males rather than size-matched cave males, likely reflecting the female preference for better-nourished (in this case: surface) males. Hence, divergent selection on body colouration indeed translates into phenotype-assortative mating in the surface ecotype, by selecting against potential migrant males. Female cave fish, by contrast, do not have a preference for the resident male phenotype, identifying natural selection against migrants imposed by the cave environment as the major driver of the observed reproductive isolation.

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Exotic fish species has caused several impacts on aquatic biodiversity. The Lago de Pátzcuaro has some well-studied exotic species, except the Lerma livebearer Poeciliopsis infans. This fish species was introduced into the Lago de Pátzcuaro before 1997 and the aspects of its biology are still unknown. In this study we assessed aspects of the trophic ecology of this exotic fish, P infans, using gut content and stable isotope analysis to understand its capacity to tolerate anthropogenic environmental degradation in the Lago de Pátzcuaro. We also determined its trophic guild position (TP) using the TrophLab Program and stable isotope. Niche breadth was calculated by standardized Levins' Index (Bi). Fish was captured with a seine during wet and dry seasons at six environmentally different sites and gut contents were obtained. We analyzed a total of 239 gut contents of P. infans. The contribution of each food item in the diet was quantified using frequency of occurrence and area percentage. The importance of each prey item was determined according to the index of relative importance (IRI), and the omnivory index (OI) was used to assess the feeding behavior. Fish were categorized by size and the diet was compared between fish sizes and sites. Dorsal muscle tissue and water hyacinth tissue was obtained for nitrogen isotope signature he fish can behave as a specialist (Bi = 0.39) or generalist (Bi = 0.68) and as a primary consumer (TROPH = 2.2; TP = 2.3) with a feeding strategy that was the same at dif- f erent sizes, seasons and sites. None of the evaluated sites showed good environmental quality. We argue that P infans can tolerate changes in water quality and feeding items availability, because it can exploit resources in multiple trophic webs. However, this species could be dependent on habitat complexity, especially in the aquatic vegetation cover.

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Exotic fish species has caused several impacts on aquatic biodiversity. The Lago de Pátzcuaro has some well-studied exotic species, except the Lerma livebearer Poeciliopsis infans. This fish species was introduced into the Lago de Pátzcuaro before 1997 and the aspects of its biology are still unknown. In this study we assessed aspects of the trophic ecology of this exotic fish, P. infans, using gut content and stable isotope analysis to understand its capacity to tolerate anthropogenic environmental degradation in the Lago de Pátzcuaro. We also determined its trophic guild position (TP) using the TrophLab Program and stable isotope. Niche breadth was calculated by standardized Levins’ Index (Bi). Fish was captured with a seine during wet and dry seasons at six environmentally different sites and gut contents were obtained. We analyzed a total of 239 gut contents of P. infans. The contribution of each food item in the diet was quantified using frequency of occurrence and area percentage. The importance of each prey item was determined according to the index of relative importance (IRI), and the omnivory index (OI) was used to assess the feeding behavior. Fish were categorized by size and the diet was compared between fish sizes and sites. Dorsal muscle tissue and water hyacinth tissue was obtained for nitrogen isotope signature (δ15N) analysis. Additionally, we measured water and habitat quality to evaluate environmental conditions at each site. We concluded that P. infans is an omnivore (OI=0.28) that consumes mainly detritus (44%), epiphytic diatoms (37%), and secondary on terrestrial insects (6%) and zooplankton (10%). The fish can behave as a specialist (Bi=0.39) or generalist (Bi=0.68) and as a primary consumer (TROPH=2.2; TP=2.3) with a feeding strategy that was the same at different sizes, seasons and sites. None of the evaluated sites showed good environmental quality. We argue that P. infans can tolerate changes in water quality and feeding items availability, because it can exploit resources in multiple trophic webs. However, this species could be dependent on habitat complexity, especially in the aquatic vegetation cover.

Las especies de peces exóticas han causado numerosos impactos sobre la biodiversidad acuática. El Lago de Pátzcuaro tiene especies exóticas bien estudiadas, excepto el Guatapote del Lerma, Poeciliopsis infans. Esta especie fue introducida en el Lago de Pátzcuaro antes de 1997 y los aspectos de su biología son aún desconocidos. Se estudiaron aspectos de la ecología trófica de este pez exótico, P. infans, mediante el uso de análisis de contenidos del tracto digestivo para entender su capacidad para tolerar la degradación ambiental antrópica en el Lago de Pátzcuaro. Lo que involucró la determinación del gremio y posición trófica (TP) con el programa TrophLab e isotopos estables. La amplitud de dieta fue calculada con el índice estandarizado de Levin (Bi). Un total de 239 tractos digestivos de P.infans fueron analizados. Los peces fueron capturados con una red tipo chinchorro durante la temporada de lluvias y estiaje en seis sitios ambientalmente distintos. La contribución de cada componente de la dieta fue cuantificada con la frecuencia de ocurrencia y el porcentaje de área. La importancia relativa de cada artículo alimentario fue determinada de acuerdo al índice de importancia relativa (IIR) y el índice de omnivoría (OI) fue usado para estimar la conducta en la forma de alimentarse. La dieta fue comparada entre tallas y entre sitios de estudio. El tejido de músculo dorsal y el tejido de lirio fueron obtenidos para determinar valores de δ15N. De manera adicional, la calidad del agua y del hábitat fue medida para evaluar la condición ambiental en cada sitio. P. infans es un omnívoro (OI=0.28) que consume principalmente detritus (44%), diatomeas epifíticas (37%) y de forma secundaria insectos terrestres (6%) y zooplancton (10%); puede comportarse como especialista (Bi=0.39) o generalista (Bi=0.68) y consumidor primario (TROPH=2.2; TP=2.3). La estrategia alimenticia fue similar entre tallas, temporadas y sitios. Ningún sitio mostró buena calidad ambiental. Los resultados del presente estudio permiten argumentar que P. infans puede tolerar cambios en la calidad del agua y en la disponibilidad de artículos alimenticios, porque puede usar recursos provenientes de múltiples redes tróficas. Sin embargo, esta especie podría ser dependiente de la complejidad del hábitat, especialmente de la cobertura de la vegetación acuática.

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A morfologia, os parâmetros citomorfométricos e os glicoconjugados presentes na pseudobrânquia de guaru, Poecilia reticulata Peter, 1859 (Cyprinodontiformes: Poeciliidae), foram investigados por microscopia de luz acoplada ao sistema de captura e análise de imagens, juntamente por histoquímica com lectinas. A anatomia microscópica indicou que P. reticulata possui pseudobrânquia glandular formada por dois lóbulos, a qual se localiza abaixo do epitélio faringiano. O órgão é constituído por parênquima vascularizado e rico em células pseudobranquiais. Esse tipo celular exibe estado citofisiológico ativo, com abundante sistema de biomembranas e ausência de óstio na superfície apical,que por sua vez é encontrado nas células ricas em mitocôndrias das holobrânquias. Assim, indica-se que as células da pseudobrânquia se distinguem das células das holobrânquias em relação à morfologia, histoquímica e fisiologia. Em decorrência dessas características intrínsecas, a pseudobrânquia de alevinos do guaru pode desempenhar funções não respiratórias nas fases iniciais do desenvolvimento. Além disso, a caracterização da pseudobrânquia do guaru possibilitará estudos futuros sobre o efeito de poluentes aquáticos em espécies biomonitoras, como P. reticulata.(AU)

The morphology, cytomorphometric parameters, and glycoconjugates present in the pseudo-gill of guppy, Poecilia reticulata Peter, 1859 (Cyprinodontiformes: Poeciliidae), were investigated by light microscopy coupled to image capture and analysis system, and also by lectin histochemistry. The microscopic anatomy indicates that P. reticulata has a glandular pseudo-gill formed by two lobes, located underneath the pharynx epithelium. The organ is formed by vascularized parenchyma rich in pseudo-gill cells. This cell type exhibits active cytophysiological state with an abundant system of biomembranes and lacking of ostium in apical surface, which in turn is found in the mitochondria-rich cells of the holobranch. This indicates that the pseudo-gill cells distinguishe from the holobranch cells in their morphology, histochemistry and physiology. Due to these intrinsic characteristics, the pseudo-gill of guppy fingerlings may have non-respiratory function in the initial phase of their development. The characterization of guppy's pseudo-gill could facilitate further studies about the effect of water pollutants on biomonitor species, such as P. reticulata.(AU)

Assuntos

RESUMO

A morfologia, os parâmetros citomorfométricos e os glicoconjugados presentes na pseudobrânquia de guaru, Poecilia reticulata Peter, 1859 (Cyprinodontiformes: Poeciliidae), foram investigados por microscopia de luz acoplada ao sistema de captura e análise de imagens, juntamente por histoquímica com lectinas. A anatomia microscópica indicou que P. reticulata possui pseudobrânquia glandular formada por dois lóbulos, a qual se localiza abaixo do epitélio faringiano. O órgão é constituído por parênquima vascularizado e rico em células pseudobranquiais. Esse tipo celular exibe estado citofisiológico ativo, com abundante sistema de biomembranas e ausência de óstio na superfície apical,que por sua vez é encontrado nas células ricas em mitocôndrias das holobrânquias. Assim, indica-se que as células da pseudobrânquia se distinguem das células das holobrânquias em relação à morfologia, histoquímica e fisiologia. Em decorrência dessas características intrínsecas, a pseudobrânquia de alevinos do guaru pode desempenhar funções não respiratórias nas fases iniciais do desenvolvimento. Além disso, a caracterização da pseudobrânquia do guaru possibilitará estudos futuros sobre o efeito de poluentes aquáticos em espécies biomonitoras, como P. reticulata.

The morphology, cytomorphometric parameters, and glycoconjugates present in the pseudo-gill of guppy, Poecilia reticulata Peter, 1859 (Cyprinodontiformes: Poeciliidae), were investigated by light microscopy coupled to image capture and analysis system, and also by lectin histochemistry. The microscopic anatomy indicates that P. reticulata has a glandular pseudo-gill formed by two lobes, located underneath the pharynx epithelium. The organ is formed by vascularized parenchyma rich in pseudo-gill cells. This cell type exhibits active cytophysiological state with an abundant system of biomembranes and lacking of ostium in apical surface, which in turn is found in the mitochondria-rich cells of the holobranch. This indicates that the pseudo-gill cells distinguishe from the holobranch cells in their morphology, histochemistry and physiology. Due to these intrinsic characteristics, the pseudo-gill of guppy fingerlings may have non-respiratory function in the initial phase of their development. The characterization of guppy's pseudo-gill could facilitate further studies about the effect of water pollutants on biomonitor species, such as P. reticulata.

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RESUMO

Fish and other aquatic vertebrates use their mechanosensory lateral line to detect objects and motion in their immediate environment. Differences in lateral line morphology have been extensively characterized among species; however, intraspecific variation remains largely unexplored. In addition, little is known about how environmental factors modify development of lateral line morphology. Predation is one environmental factor that can act both as a selective pressure causing genetic differences between populations, and as a cue during development to induce plastic changes. Here, we test whether variation in the risk of predation within and among populations of Trinidadian guppies (Poecilia reticulata) influences lateral line morphology. We compared neuromast arrangement in wild-caught guppies from distinct high- and low-predation population pairs to examine patterns associated with differences in predation pressure. To distinguish genetic and environmental influences, we compared neuromast arrangement in guppies from different source populations reared with and without exposure to predator chemical cues. We found that the distribution of neuromasts across the body varies between populations based on both genetic and environmental factors. To the best of our knowledge, this study is the first to demonstrate variation in lateral line morphology based on environmental exposure to an ecologically relevant stimulus.

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