Abstract
BackgroundRecent studies have demonstrated that Bayesian species delimitation based on the multispecies coalescent model can produce inaccurate results by misinterpreting population splits as species divergences. An approach based on the genealogical divergence index (gdi) was shown to be a viable alternative, especially for delimiting allopatric populations where gene flow is low. We implemented these analyses to assess species boundaries in Southeast Asian toads, a group that is understudied and characterized by numerous unresolved species complexes.ResultsMultilocus phylogenetic analyses showed that deep evolutionary relationships including the genera Sigalegalephrynus, Ghatophryne, Parapelophryne, Leptophryne, Pseudobufo, Rentapia, and Phrynoides remain unresolved. Comparison of genetic divergences revealed that intraspecific divergences among allopatric populations of Pelophyrne signata (Borneo vs. Peninsular Malaysia), Ingerophrynus parvus (Peninsular Malaysia vs. Myanmar), and Leptophryne borbonica (Peninsular Malaysia, Java, Borneo, and Sumatra) are consistent with interspecific divergences of other Southeast Asian bufonid taxa. Conversely, interspecific divergences between Pelophryne guentheri/P. api, Ansonia latiffi/A. leptopus, and I. gollum/I. divergens were low (< 3%) and consistent with intraspecific divergences of other closely related taxa. The BPP analysis produced variable results depending on prior settings and priors estimated from empirical data produced the best results that were also congruent with the gdi analysis.ConclusionsThis study showed that the evolutionary history of Southeast Asian toads is difficult to resolve and numerous relationships remain ambiguous. Although some results from the species delimitation analyses were inconclusive, they were nevertheless efficacious at identifying potential new species and taxonomic incompatibilities for future in-depth investigation. We also demonstrated the sensitivity of BPP to different priors and that careful selection priors based on empirical data can greatly improve the analysis. Finally, the gdi can be a robust tool to complement other species delimitation methods.
Highlights
Recent studies have demonstrated that Bayesian species delimitation based on the multispecies coalescent model can produce inaccurate results by misinterpreting population splits as species divergences
The maximum likelihood (ML) tree was poorly supported at the basal nodes, including the genera Sigalegalephrynus, Parapelophryne, Leptophryne, Pseudobufo, Ghatophryne, Rentapia, and Phrynoidis
The BEAST tree differed only in the placement of the genus Ghatophryne, which was recovered as the sister lineage to Parapelophryne + Leptophryne, as opposed to the ML tree, where it was the sister lineage to Rentapia + Phrynoidis
Summary
Recent studies have demonstrated that Bayesian species delimitation based on the multispecies coalescent model can produce inaccurate results by misinterpreting population splits as species divergences. Taxonomic nomenclature is constantly in flux [2,3,4,5,6,7,8,9,10,11], as it attempts to keep pace with the increasing frequency at which new species are being described (especially cryptic species) and revised [12,13,14,15,16,17,18,19,20,21,22,23,24,25,26] These insights have improved our understanding of Southeast Asian amphibian biodiversity considerably, many taxa have yet to be sequenced or subjected to molecular analyses, and more fine-scale geographic sampling is still needed to adequately characterize species boundaries and distribution ranges. Most research focused on small subsets relating to specific taxon groups, thereby precluding the detection of broad biodiversity and evolutionary patterns that can only be revealed by more comprehensive studies conducted at a broader scale [5]
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