RESUMO
Animal signals evolve in an ecological context. Locally adapting animal sexual signals can be especially important for initiating or reinforcing reproductive isolation during the early stages of speciation. Previous studies have demonstrated that dewlap colour in Anolis lizards can be highly variable between populations in relation to both biotic and abiotic adaptive drivers at relatively large geographical scales. Here, we investigated differentiation of dewlap coloration among habitat types at a small spatial scale, within multiple islands of the West Indies, to test the hypothesis that similar local adaptive processes occur over smaller spatial scales. We explored variation in dewlap coloration in the most widespread species of anole, Anolis sagrei, across three characteristic habitats spanning the Bahamas and the Cayman Islands, namely beach scrub, primary coppice forest and mangrove forest. Using reflectance spectrometry paired with supervised machine learning, we found significant differences in spectral properties of the dewlap between habitats within small islands, sometimes over very short distances. Passive divergence in dewlap phenotype associated with isolation-by-distance did not seem to explain our results. On the other hand, these habitat-specific dewlap differences varied in magnitude and direction across islands, and thus, our primary test for adaptation-parallel responses across islands-was not supported. We suggest that neutral processes or selection could be involved in several ways, including sexual selection. Our results shed new light on the scale at which signal colour polymorphism can be maintained in the presence of gene flow, and the relative role of local adaptation and other processes in driving these patterns of dewlap colour variation across islands.
Assuntos
Lagartos , Animais , Cor , Ecossistema , Fluxo Gênico , Lagartos/genética , Índias OcidentaisRESUMO
Hybridization is among the evolutionary mechanisms most frequently hypothesized to drive the success of invasive species, in part because hybrids are common in invasive populations. One explanation for this pattern is that biological invasions coincide with a change in selection pressures that limit hybridization in the native range. To investigate this possibility, we studied the introduction of the brown anole (Anolis sagrei) in the southeastern United States. We find that native populations are highly genetically structured. In contrast, all invasive populations show evidence of hybridization among native-range lineages. Temporal sampling in the invasive range spanning 15 y showed that invasive genetic structure has stabilized, indicating that large-scale contemporary gene flow is limited among invasive populations and that hybrid ancestry is maintained. Additionally, our results are consistent with hybrid persistence in invasive populations resulting from changes in natural selection that occurred during invasion. Specifically, we identify a large-effect X chromosome locus associated with variation in limb length, a well-known adaptive trait in anoles, and show that this locus is often under selection in the native range, but rarely so in the invasive range. Moreover, we find that the effect size of alleles at this locus on limb length is much reduced in hybrids among divergent lineages, consistent with epistatic interactions. Thus, in the native range, epistasis manifested in hybrids can strengthen extrinsic postmating isolation. Together, our findings show how a change in natural selection can contribute to an increase in hybridization in invasive populations.
Assuntos
Lagartos/genética , Seleção Genética , Animais , Variação Genética , Espécies Introduzidas , Hibridização de Ácido NucleicoRESUMO
Hurricanes are catastrophically destructive. Beyond their toll on human life and livelihoods, hurricanes have tremendous and often long-lasting effects on ecological systems1,2. Despite many examples of mass mortality events following hurricanes3-5, hurricane-induced natural selection has not previously been demonstrated. Immediately after we finished a survey of Anolis scriptus-a common, small-bodied lizard found throughout the Turks and Caicos archipelago-our study populations were battered by Hurricanes Irma and Maria. Shortly thereafter, we revisited the populations to determine whether morphological traits related to clinging capacity had shifted in the intervening six weeks and found that populations of surviving lizards differed in body size, relative limb length and toepad size from those present before the storm. Our serendipitous study, which to our knowledge is the first to use an immediately before and after comparison6 to investigate selection caused by hurricanes, demonstrates that hurricanes can induce phenotypic change in a population and strongly implicates natural selection as the cause. In the decades ahead, as extreme climate events are predicted to become more intense and prevalent7,8, our understanding of evolutionary dynamics needs to incorporate the effects of these potentially severe selective episodes9-11.
Assuntos
Tempestades Ciclônicas , Desastres , Lagartos/anatomia & histologia , Seleção Genética , Animais , Tamanho Corporal , Extremidades/anatomia & histologia , Feminino , Fêmur/anatomia & histologia , Úmero/anatomia & histologia , Ilhas , Masculino , Índias OcidentaisRESUMO
We report a new chameleon-like Anolis species from Hispaniola that is ecomorphologically similar to congeners found only on Cuba. Lizards from both clades possess short limbs and a short tail and utilize relatively narrow perches, leading us to recognize a novel example of ecomorphological matching among islands in the well-known Greater Antillean anole radiation. This discovery supports the hypothesis that the assembly of island faunas can be substantially deterministic and highlights the continued potential for basic discovery to reveal new insights in well-studied groups. Restricted to a threatened band of midelevation transitional forest near the border of the Dominican Republic and Haiti, this new species appears to be highly endangered.
Assuntos
Lagartos/anatomia & histologia , Lagartos/classificação , Animais , Evolução Biológica , República Dominicana , Feminino , Haiti , Lagartos/genética , Masculino , Filogeografia , Análise de Sequência de DNA , Especificidade da EspécieRESUMO
The distichus species group includes six species and 21 subspecies of trunk ecomorph anoles distributed across Hispaniola and its satellite islands as well as the northern Bahamas. Although this group has long served as a model system for studies of reproductive character displacement, adaptation, behavior and speciation, it has never been the subject of a comprehensive phylogenetic analysis. Our goal here is to generate a multilocus phylogenetic dataset (one mitochondrial and seven nuclear loci) and to use this dataset to infer phylogenetic relationships among the majority of the taxa assigned to the distichus species group. We use these phylogenetic trees to address three topics about the group's evolution. First, we consider longstanding taxonomic controversies about the status of several species and subspecies assigned to the distichus species group. Second, we investigate the biogeographic history of the group and specifically test the hypotheses that historical division of Hispaniola into two paleo-islands contributed to the group's diversification and that Bahamian and Hispaniolan satellite island populations are derived from colonists from the main Hispaniolan landmass. Finally, third, we use comparative phylogenetic analyses to test the hypothesis that divergence between pale yellow and darkly pigmented orange or red dewlap coloration has occurred repeatedly across the distichus species group.
Assuntos
Evolução Biológica , Lagartos/classificação , Filogenia , Animais , Bahamas , Teorema de Bayes , Núcleo Celular/genética , DNA Mitocondrial/genética , Ilhas , Lagartos/genética , Modelos Genéticos , Filogeografia , Pigmentação , Análise de Sequência de DNARESUMO
The freshwater mussel family Hyriidae (Mollusca: Bivalvia: Unionida) has a disjunct trans-Pacific distribution in Australasia and South America. Previous phylogenetic analyses have estimated the evolutionary relationships of the family and the major infra-familial taxa (Velesunioninae and Hyriinae: Hyridellini in Australia; Hyriinae: Hyriini, Castaliini, and Rhipidodontini in South America), but taxon and character sampling have been too incomplete to support a predictive classification or allow testing of biogeographical hypotheses. We sampled 30 freshwater mussel individuals representing the aforementioned hyriid taxa, as well as outgroup species representing the five other freshwater mussel families and their marine sister group (order Trigoniida). Our ingroup included representatives of all Australian genera. Phylogenetic relationships were estimated from three gene fragments (nuclear 28S, COI and 16S mtDNA) using maximum parsimony, maximum likelihood, and Bayesian inference, and we applied a Bayesian relaxed clock model calibrated with fossil dates to estimate node ages. Our analyses found good support for monophyly of the Hyriidae and the subfamilies and tribes, as well as the paraphyly of the Australasian taxa (Velesunioninae, (Hyridellini, (Rhipidodontini, (Castaliini, Hyriini)))). The Hyriidae was recovered as sister to a clade comprised of all other Recent freshwater mussel families. Our molecular date estimation supported Cretaceous origins of the major hyriid clades, pre-dating the Tertiary isolation of South America from Antarctica/Australia. We hypothesize that early diversification of the Hyriidae was driven by terrestrial barriers on Gondwana rather than marine barriers following disintegration of the super-continent.
Assuntos
Evolução Biológica , Bivalves/classificação , Filogenia , Animais , Austrália , Teorema de Bayes , Bivalves/genética , Primers do DNA , DNA Mitocondrial/genética , Fósseis , Funções Verossimilhança , Modelos Genéticos , Análise de Sequência de DNA , América do SulRESUMO
The pattern of reproductive character displacement (RCD)-in which traits associated with reproductive isolation are more different where two species occur together than where they occur in isolation-is frequently attributed to reinforcement, a process during which natural selection acting against maladaptive mating events leads to enhanced prezygotic isolation between species or incipient species. One of the first studies of RCD to include molecular genetic data was described 40 years ago in a complex of Haitian trunk anole lizards using a small number of allozyme loci. In this example, Anolis caudalis appears to experience divergence in the color and pattern of an extensible throat fan, or dewlap, in areas of contact with closely related species at the northern and southern limits of its range. However, this case study has been largely overlooked for decades; meanwhile, explanations for geographic variation in dewlap color and pattern have focused primarily on adaptation to local signalling environments. We reinvestigate this example using amplified fragment length polymorphism (AFLP) genome scans, mtDNA sequence data, information on dewlap phenotypes and GIS data on environmental variation to test the hypothesis of RCD generated by reinforcement in Haitian trunk anoles. Together, our phenotypic and genetic results are consistent with RCD at the southern and northern limits of the range of A. caudalis. We evaluate the evidence for reinforcement as the explanation for RCD in Haitian trunk anoles, consider alternative explanations and provide suggestions for future work on the relationship between dewlap variation and speciation in Haitian trunk anoles.
Assuntos
Fluxo Gênico/genética , Variação Genética , Lagartos/genética , Mitocôndrias/genética , Isolamento Reprodutivo , Adaptação Biológica/genética , Análise do Polimorfismo de Comprimento de Fragmentos Amplificados , Animais , DNA Mitocondrial/análise , Especiação Genética , Haiti , NADH Desidrogenase/genética , Seleção Genética , Alinhamento de Sequência , Análise de Sequência de DNARESUMO
Doradidae is a monophyletic catfish family endemic to continental South America, and composed of 93 valid species here placed in 31 genera. Existing phylogenetic hypotheses for Doradidae are derived from comprehensive analyses of morphological data, and a single molecular-based study on a limited subset of taxa. To provide a robust molecular phylogeny commensurate with those based on morphology, we gathered original and published sequence data for 86 species-level taxa (at least 70 valid species plus 16 new or questionably nominal species) and all genera of Doradidae, as well as 10 species (nine genera) of Auchenipteridae and three species and genera of Aspredinidae as outgroups. 3011 base pairs were aligned for two mitochondrial genes (cytochrome c oxidase subunit 1, and 16S ribosomal RNA) and one nuclear gene (recombination activating gene 1), and analyzed for a total of 143 specimens (130 doradids, 10 auchenipterids and three aspredinids). Tree topologies generated by Maximum Parsimony, Maximum Likelihood, and Bayesian analyses were largely congruent, and are compared to existing phylogenies based on morphology and molecules. Although many of the relationships supported by our molecular analyses corroborated those based on morphology, others are newly hypothesized or remain in conflict. The monotypic Wertheimeria, Franciscodoras and Kalyptodoras, for example, form a newly proposed clade, and the subfamily Astrodoradinae is placed at the base of the doradid tree. The monotypic Doraops and Centrochir, endemic to Caribbean drainages north and west of the Andes, are sister to Pterodoras and Platydoras, respectively, two genera that are widely distributed in Atlantic drainages. Additional biogeographic implications are discussed for hypothesized relationships among doradids. Molecular evidence strongly supports synonymization of monotypic Merodoras with Amblydoras, and transfer of Amblydoras bolivarensis to genus Scorpiodoras. Furthermore, we consider Opsodoras ternetzi to be more properly placed in the genus Nemadoras. The genus Opsodoras may warrant synonymization with Hemidoras, and the monophyly of genus Ossancora is not supported; however, we refrain from taxonomic decisions regarding those taxa until a broader spectrum of doradids can be submitted to further morphological and molecular phylogenetic analyses.