Delimiting genetic units in Neotropical toads under incomplete lineage sorting and hybridization

Abstract

BackgroundDelimiting genetic units is useful to enhance taxonomic discovery and is often the first step toward understanding evolutionary mechanisms generating diversification. The six species within the Rhinella crucifer group of toads were defined under morphological criteria alone. Previous data suggest limited correspondence of these species to mitochondrial lineages, and morphological intergradation at transitions between forms suggests hybridization. Here we extensively sampled populations throughout the geographic distribution of the group and analyzed mitochondrial and nuclear sequence data to delimit genetic units using tree–based and allele frequency–based approaches.ResultsThese approaches yielded complementary results, with allele frequency-based methods performing unexpectedly well given the limited number of loci examined. Both mitochondrial and nuclear markers supported a genetic structure of five units within the group, with three of the inferred units distributed within its main range, while two other units occur in separate isolates. The inferred units are mostly discordant with currently described forms: unequivocal association exists for only two of the six species in the group. Genetic evidence for hybridization exists for two pairs of units, with clear cyto–nuclear allele mixing observed in one case.ConclusionsOur results confirmed that current taxonomy does not represent evolutionary units in the Rhinella crucifer group. Correspondence between genetically distinguishable units and the currently recognized species is only possible for Rhinella henseli and R. inopina. The recognition of other species relies on the reassessment of the geographic range of R. crucifer, the examination of the type series of R. ornata for hybrids, and on the use of additional markers to verify the genetic distinctiveness of R. abei. We state that R. pombali should not remain a valid species since its description appears to be based on hybrids, and that the name R. pombali should be considered a synonym of both R. crucifer and R. ornata. The fifth inferred but undescribed genetic unit may represent a new species. Our results underscore the potential of the R. crucifer species group to contribute to a better understanding of diversification processes and hybridization patterns in the Neotropics, and provide the basis for future evolutionary and taxonomic studies.

Ancient divergence and recent population expansion in a leaf frog endemic to the southern Brazilian Atlantic forest

“…Multilocus approaches based on the coalescent theory and/ or allele frequency have been successful in combining the information of different genes to reveal population groups even with reduced genome sampling and in the presence of incomplete lineage sorting and/or hybridization (Fusinatto et al 2013;Thomé et al 2012). Here, the two lineages of P. distincta revealed by mtDNA analysis were unambiguously corroborated by multilocus analyses, albeit with some evidence of intermediate genomes suggesting either incomplete lineage sorting or mixing (Fig.…”

Phylogenetic relationships of toads of the Rhinella granulosa group (Anura: Bufonidae): a molecular perspective with comments on hybridization and introgression

“…However, under experimental conditions, it is known that some species of Bufonidae have high rates of interspecific hybridization and survival of hybrids (Blair, ; Malone and Fontenot, ). Overall, these biological and reproductive characteristics could provide recurrent opportunities for genetic exchange between different species, as is noticeable in the R. granulosa (this work), the R. crucifer (Thomé et al., ), and the R. marina (Sequeira et al., ) groups, Bufotes (Stöck et al., ; Colliard et al., ), the Anaxyrus americanus group (Fontenot et al., ), and Bufo (Yamazaki et al., ; Garcia‐Porta et al., ; but see Arntzen et al., ) where extensive nuclear and/or mitochondrial introgression was observed. Moreover, Stöck et al.…”

A new species of Chiasmocleis (Microhylidae, Gastrophryninae) from the Atlantic Forest of Espírito Santo State, Brazil

“…Recent molecular phylogenies of anuran, including work on species from the Brazilian Atlantic Forest, did not recovered as monophyletic the species groups clustered based mostly on morphology (Amaro et al 2009, Canedo and Haddad 2012, Fouquet et al 2012, Thomé et al 2012). …”