Dr Avrajjal Ghosh is the first PhD student to graduate from BioGeoSys. At the lab, he worked on the biogeographic history of three endemic genera of skinks. A year on, he gives a brief description of what his PhD was about and conclusions it has brought. Currently, Dr Ghosh is a post-doctoral fellow at Charles University, Prague.
Dispersal events, rather than Gondwanan vicariance, have shaped the modern distribution of biota within the Indian subcontinent, particularly following late Cretaceous volcanism. During its northward drift and subsequent collision with Asia, favorable climates enabled colonization events and in situ radiations, giving rise to endemic lineages. Ancient lizards like the lizard family Scincidae (skinks) offer valuable insights into such evolutionary processes. My Ph.D. investigated the biogeographic histories of three endemic Lygosomine genera—Ristella and Kaestlea from the Western Ghats, and Lankascincus from Sri Lanka.
Using a multi-locus dataset, I found that Ristella and Lankascincus are sister taxa within the Eugongyline group, while Kaestlea is allied to the Sphenomorphus group. Ancestral range analyses suggested that all three groups had Asian ancestors and arrived on the Indian subcontinent following two independent transoceanic dispersal events, one during the late Paleocene (around 60 million years ago) and the other during the early Eocene (52 million years ago).
Further analysis of Ristella and Kaestlea, using phylogenetics, species delimitation, haplotype networks, and distribution modeling, revealed cryptic diversity shaped by geo-climatic factors and physical barriers in the Western Ghats, such as the Palghat and Shencottah Gaps. In Kaestlea, diversification occurred during the Pliocene-Pleistocene, possibly facilitated by climatically conducive dispersal corridors during glacial periods. Within Ristella, I found a case of geo-climatic separation between two distinct morphotypes that were also separated phylogenetically. These skinks started diversifying in the climatically stable southern Western Ghats during the early Miocene. Lineage accumulation in these strictly forest-dwelling skinks was majorly during the Late Miocene-Early Pliocene, indicating a case of aridity-induced vicariance. Finally, with the help of citizen science platforms, a coastal Indian population of Lankascincus fallax, previously thought to be Sri Lankan endemic, was discovered. This Indian population likely represents a case of human-mediated dispersal, as paleoclimatic data did not support natural connectivity.