RESUMO
The West Indian avifauna has provided fundamental insights into island biogeography, taxon cycles, and the evolution of avian behavior. Our interpretations, however, should rely on robust hypotheses of evolutionary relationships and consistent conclusions about taxonomic status in groups with many endemic island populations. Here we present a phylogenetic study of the West Indian thrashers, tremblers, and allies, an assemblage of at least 5 species found on 29 islands, including what is considered the Lesser Antilles' only avian radiation. We improve on previous phylogenetic studies of this group by using double-digest restriction site-associated DNA sequencing (ddRAD-seq) to broadly sample loci scattered across the nuclear genome. A variety of analyses, based on either nucleotide variation in 2223 loci recovered in all samples or at 13,282 loci confidently scored as present or absent in all samples, converged on a single well-supported phylogenetic hypothesis. Results indicate that the resident West Indian taxa form a monophyletic group, exclusive of the Neotropical-Nearctic migratory Gray Catbird Dumetella carolinensis, which breeds in North America; this outcome differs from earlier studies suggesting that Gray Catbird was nested within a clade of island resident species. Thus, our findings imply a single colonization of the West Indies without the need to invoke a subsequent 'reverse colonization' of the mainland by West Indian taxa. Additionally, our study is the first to sample both endemic subspecies of the endangered White-breasted Thrasher Ramphocinclus brachyurus. We find that these subspecies have a long history of evolutionary independence with no evidence of gene flow, and are as genetically divergent from each other as other genera in the group. These findings support recognition of R. brachyurus (restricted to Martinique) and the Saint Lucia Thrasher R. sanctaeluciae as two distinct, single-island endemic species, and indicate the need to re-evaluate conservation plans for these taxa. Our results demonstrate the utility of phylogenomic datasets for generating robust systematic hypotheses.
Assuntos
Sequência Conservada , Passeriformes/classificação , Passeriformes/genética , Filogenia , Filogeografia , Animais , Sequência de Bases , DNA Mitocondrial/genética , Mapeamento por Restrição , Análise de Sequência de DNA , Especificidade da Espécie , Índias OcidentaisRESUMO
Speciation is a continuous and dynamic process, and studying organisms during the early stages of this process can aid in identifying speciation mechanisms. The mallard (Anas platyrhynchos) and Mexican duck (A. [p.] diazi) are two recently diverged taxa with a history of hybridization and controversial taxonomy. To understand their evolutionary history, we conducted genomic scans to characterize patterns of genetic diversity and divergence across the mitochondrial DNA (mtDNA) control region, 3523 autosomal loci and 172 Z-linked sex chromosome loci. Between the two taxa, Z-linked loci (ΦST = 0.088) were 5.2 times more differentiated than autosomal DNA (ΦST = 0.017) but comparable to mtDNA (ΦST = 0.092). This elevated Z differentiation deviated from neutral expectations inferred from simulated data that incorporated demographic history and differences in effective population sizes between marker types. Furthermore, 3% of Z-linked loci, compared to <0.1% of autosomal loci, were detected as outlier loci under divergent selection with elevated relative (ΦST ) and absolute (dXY ) estimates of divergence. In contrast, the ratio of Z-linked and autosomal differentiation among the seven Mexican duck sampling locations was close to 1:1 (ΦST = 0.018 for both markers). We conclude that between mallards and Mexican ducks, divergence at autosomal markers is largely neutral, whereas greater divergence on the Z chromosome (or some portions thereof) is likely the product of selection that has been important in speciation. Our results contribute to a growing body of literature indicating elevated divergence on the Z chromosome and its likely importance in avian speciation.
Assuntos
Patos/genética , Evolução Molecular , Especiação Genética , Cromossomos Sexuais/genética , Animais , DNA Mitocondrial/genética , Patos/classificação , Genética Populacional , México , Modelos Genéticos , Dados de Sequência Molecular , Densidade Demográfica , Análise de Sequência de DNA , Estados UnidosRESUMO
One of the most widely distributed bats in the New World, the big brown bat (Eptesicus fuscus) exhibits well-documented geographic variation in morphology and life history traits, suggesting the potential for significant phylogeographic structure as well as adaptive differentiation among populations. In a pattern broadly consistent with morphologically defined subspecies, we found deeply divergent mitochondrial lineages restricted to different geographic regions. In contrast, sequence data from two nuclear loci suggest a general lack of regional genetic structure except for peripheral populations in the Caribbean and Mexico/South America. Coalescent analyses suggest that the striking difference in population structure between genomes cannot be attributed solely to different rates of lineage sorting, but is likely due to male-mediated gene flow homogenizing nuclear genetic diversity across most of the continental range. Despite this ongoing gene flow, selection has apparently been effective in producing and maintaining adaptive differentiation among populations, while strong female site fidelity, maintained over the course of millions of years, has produced remarkably deep divergence among geographically isolated matrilines. Our results highlight the importance of evaluating multiple genetic markers for a more complete understanding of population structure and history.