Morphotypes or distinct species? A multilocus assessment of two East Asian scimitar babblers (Aves,Timaliidae)

In birds, widespread species complexes often exhibit dramatic plumage differences across their distribution, which can give rise to discordance between morphotypes and phylogroups. Accurate identification of species diversity may require an integrated approach in which multilocus genetic data are used for inference and further corroborated by ecological, morphometric or behavioural data. Pomatorhinus gravivox and P. swinhoei, which were formerly considered component races of P. erythrogenys, were recently split using a delimitation system that mainly relied on the quantification of differences in phenotypic traits. We therefore carried out a reassessment of this taxonomic recommendation by conducting phylogenetic and population genetic analyses with multilocus genetic data. A deep mitochondrial split with a Kimura 2-parameter distance of 0.061 was observed, mainly corresponding to the two morphologically defined species. However, one individual from P. swinhoei harboured a haplotype of P. gravivox. Individual-based analyses of nuclear loci identified two distinct clusters that were exactly congruent with the two species. BPP delimitation also provided support for the separation. These congruencies support the notion that these two taxa are best regarded as two separate species. The presence of the P. gravivox mitochondrial haplotype in P. swinhoei was most likely a result of hybridization, due to the clear separation of nuclear loci. The speciation might be attributed to paleoclimatic changes but requires further evaluation due to the likelihood of ecological speciation. This study was in accordance with the results inferred from the quantitative system but highlighted the importance of sampling various data, especially in contact zones, in the study of taxonomy and speciation history.