Mitochondrial phylogeny of the troidine genera Atrophaneura and Byasa (Lepidoptera: Papilionidae) clarifies species boundaries and highlights the role of the Hengduan Mountains and Sundaland in their biogeographic history

The Palaearctic, Indomalayan, and Australasian biogeographic regions are known for their high butterfly species diversity and complex geographic variation, yet the mechanisms shaping this biogeographic pattern remain poorly understood. Here, we investigate the macroevolutionary processes driving the temporal and geographical diversification of the troidine genera Atrophaneura and Byasa (Papilionidae: Troidini). We sequenced three mitochondrial DNA sequences for 109 specimens, representing all species, and performed Bayesian and maximum-likelihood phylogenetic inferences to refine species boundaries. Subsequent Bayesian molecular dating analyses were carried out to estimate divergence times, and maximum-likelihood model were used to reconstruct the biogeographic history and estimate diversification rates for Atrophaneura and Byasa. Our results show that Atrophaneura and Byasa originated around 19 million years ago in a broad range including Sundaland, Indochina, South China, and the Hengduan Mountains. A vicariance event likely led to the origin of Atrophaneura in Sundaland and subsequently dispersed to adjacent regions, while Byasa originated in the Hengduan Mountains. We further find that the diversification of the clade decreased toward the present and is more likely tied to temperature variations or sea-level fluctuations, which emerged as the putative drivers of their diversification. Our research underscores the significance of the Sundaland and Hengduan Mountains as independent biogeographic regions in the evolutionary history of these butterfly species. Our findings provide valuable insights into the distinct evolutionary trajectories of these two sister genera, highlighting the importance of both geographic and climatic factors in shaping biodiversity patterns in this mega-diverse tropical region.