RESUMO
Perhaps the most important recent advance in species delimitation has been the development of model-based approaches to objectively diagnose species diversity from genetic data. Additionally, the growing accessibility of next-generation sequence data sets provides powerful insights into genome-wide patterns of divergence during speciation. However, applying complex models to large data sets is time-consuming and computationally costly, requiring careful consideration of the influence of both individual and population sampling, as well as the number and informativeness of loci on species delimitation conclusions. Here, we investigated how locus number and information content affect species delimitation results for an endangered Mexican salamander species, Ambystoma ordinarium. We compared results for an eight-locus, 137-individual data set and an 89-locus, seven-individual data set. For both data sets, we used species discovery methods to define delimitation models and species validation methods to rigorously test these hypotheses. We also used integrated demographic model selection tools to choose among delimitation models, while accounting for gene flow. Our results indicate that while cryptic lineages may be delimited with relatively few loci, sampling larger numbers of loci may be required to ensure that enough informative loci are available to accurately identify and validate shallow-scale divergences. These analyses highlight the importance of striking a balance between dense sampling of loci and individuals, particularly in shallowly diverged lineages. They also suggest the presence of a currently unrecognized, endangered species in the western part of A. ordinarium's range.
Assuntos
Ambystoma mexicanum/genética , Espécies em Perigo de Extinção , Loci Gênicos , Animais , México , Modelos Genéticos , FilogeniaRESUMO
A long-standing question in evolutionary biology is what becomes of adaptive traits when a species expands its range into novel environments. Here, we report the results of a study on an adaptive colour pattern polymorphism (stripes) of the coqui frog, Eleutherodactylus coqui, following its introduction to Hawaii from Puerto Rico. We compared population differentiation (Φ ST and F ST ) for the stripes locus--which underlies this colour pattern polymorphism--with neutral microsatellite loci to test for a signature of selection among native and introduced populations. Among native populations, Φ ST and F ST for stripes were lower than expected under the neutral model, suggesting uniform balancing selection. Alternatively, among introduced populations, Φ ST and F ST for stripes did not differ from the neutral model. These results suggest that the evolutionary dynamics of this previously adaptive trait have become dominated by random genetic drift following the range expansion.
Assuntos
Anuros/genética , Deriva Genética , Seleção Genética , Animais , Cor , Evolução Molecular , Variação Genética , Genética Populacional , Havaí , Repetições de Microssatélites , Modelos Biológicos , Fenótipo , Polimorfismo Genético , Dinâmica Populacional , Porto RicoRESUMO
Many species of frog exhibit striking color and pattern polymorphisms, but the genetic bases of these traits are not known for most species. The coqui frog, Eleutherodactylus coqui, a species endemic to the island of Puerto Rico, exhibits a wide variety of color and pattern polymorphisms including 4 discrete stripe patterns on its dorsal surface and an unstriped morph. We conducted breeding experiments to determine the mode of inheritance for these 5 dorsal color patterns in E. coqui. We analyzed results from 14 different cross types, which included 1519 offspring from 71 clutches. We found that color patterns segregate at ratios consistent with a single autosomal locus, 5-allele model, in which all alleles coding for stripes are codominant and the allele coding for the unstriped morph is recessive. We propose that this locus be named "stripes" with alleles B (interocular bar), L (dorsolateral stripes), N (narrow middorsal stripe), W (wide middorsal stripe), and u (unstriped). The results of this experiment suggest the genetic basis of stripe patterns in this well-studied species and provide a model for studying the evolution and maintenance of this phenotypic polymorphism.
Assuntos
Anuros/anatomia & histologia , Anuros/genética , Padronização Corporal/genética , Pigmentação da Pele/genética , Alelos , Animais , Cruzamento , Cruzamentos Genéticos , Genes Dominantes , Genes Recessivos , Variação Genética , Haplótipos , Fenótipo , Polimorfismo Genético , Porto RicoRESUMO
The success of non-native species may depend on the genetic resources maintained through the invasion process. The Coqui (Eleutherodactylus coqui), a frog endemic to Puerto Rico, was introduced to Hawaii in the late 1980s via the horticulture trade, and has become an aggressive invader. To explore whether genetic diversity and population structure changed with the introduction, we assessed individuals from 15 populations across the Hawaiian Islands and 13 populations across Puerto Rico using six to nine polymorphic microsatellite loci and five dorsolateral colour patterns. Allelic richness (R(T)) and gene diversity were significantly higher in Puerto Rico than in Hawaii populations. Hawaii also had fewer colour patterns (two versus three to five per population) than Puerto Rico. We found no isolation by distance in the introduced range, even though it exists in the native range. Results suggest extensive mixing among frog populations across Hawaii, and that their spread has been facilitated by humans. Like previous research, our results suggest that Hawaiian Coquis were founded by individuals from sites around San Juan, but unlike previous research the colour pattern and molecular genetic data (nuclear and mtDNA) support two separate introductions, one on the island of Hawaii and one on Maui. Coquis are successful invaders in Hawaii despite the loss of genetic variation. Future introductions may increase genetic variation and potentially its range.