Isolation by geographical distance after release from Pleistocene refugia explains genetic and phenotypic variation in Xylotrupes siamensis (Coleoptera: Scarabaeidae)

Consistent and objective species delimitation is crucial to biodiversity studies, but challenges remain when conflicting taxonomic decisions have been made because different data sets and analytical methods were used to delineate species. In the rhinoceros beetle, Xylotrupes siamensis, the use of different morphological characters has resulted in taxonomic disagreement between studies. We used three molecular loci (mitochondrial CO1 and nuclear ITS2 and H3) to investigate the genetic divergence between populations exhibiting different male horn phenotypes. We also applied an approximate Bayesian computation approach to test alternative historical hypotheses that might explain the present genetic diversity among geographical populations. Furthermore, we used species distribution models to estimate the temporal variation in the geographical distribution of suitable habitats. The results show that the two phenotypic taxa within X. siamensis are not genetically structured and that their gen...