A team of researchers led by Avrajjal Ghosh from the National Institute of Science Education and Research, Odisha, has discovered a population of Lankascincus fallax, a species of skink perceived to be endemic to Sri Lanka, on the western coast of India. The study gauges at the possibilities of the dispersal of this species to be human-mediated.
India and Sri Lanka have long shared a common diversity of species. In-situ diversification of species within various regions of the Indian subcontinent has led to high levels of endemism, particularly in biodiversity hotspots like the Western Ghats. Fluctuating sea levels gave rise to land bridges, which led to the natural dispersal of multiple taxa between the two countries.
In 2021, with the help of citizen science, naturalists and researchers stumbled upon an interesting skink species on the Indian west coast which was hitherto known only from Sri Lanka. Researchers from the National Institute of Science Education and Research, Odisha; Indian Institute of Science, Bangalore; Centre for Cellular and Molecular Biology, Hyderabad; and Wayanad Wild, Kerala, collected samples from Kerala, where multiple specimens were found. Eager to understand its origin, they started a project using an integrative approach, comprising morphological measurements, molecular phylogenetics, divergence dating analysis, and species distribution modeling.
Aided by the morphological comparisons along with the phylogeny researchers identified the specimens as Lankascincus fallax, which is endemic to Sri Lanka. Through their divergence dating analysis, a method that helps determine when two species diverged from a common ancestor, the researchers found that the genus Lankascinus diverged from its sister genus Ristella, which is endemic to the Western Ghats in India, in the late Palaeocene (56 million years ago). Lankascincus fallax is over 2.8 million years old and the Indian population, which was found in Kerala, split from a Sri Lankan counterpart over 1.7 million years ago.
To understand the journey of the species from Sri Lanka to the southwestern Indian coast, researchers used species distribution modelling using present and past climatic data. No suitable terrestrial corridor was found during the middle-late Pliocene to the present time that could have aided the dispersal of this species to mainland India. The occurrence of the species along the coasts and lack of evidence of a possible terrestrial corridor indicates that the dispersal is perhaps human-mediated.
Although the divergence date predates human presence in this landscape, researchers caution that the old divergence date is directly correlated with high levels of genetic divergence between the Kerala and Sri Lankan populations which originate from different source populations. Another possible reason for its dispersal could be transoceanic currents. While the species has also been recorded in the nearby islands of Maldives, there’s no evidence of an established population or whether it arrived there from India or Sri Lanka.
Such studies raise several questions: Does the species remain endemic to Sri Lanka, or could it potentially become invasive in its newly discovered range in India? “This is an interesting question, and I’ve reflected on it as well,” says Ghosh, lead author of the study.
Many believe the species is still endemic to Sri Lanka, though a better phrase would be ‘endemic to Sri Lanka, but possibly accidentally introduced to India and the Maldives.
To understand the extent of invasion, Ghosh explains, one would need to show that the species not only survives but also has the tendency to become invasive —impacting local ecosystems — through a different method of investigation.
“Given the presence of multiple populations across a large area (spanning at least 275 km in length), it is reasonable to conclude that the species is breeding and spreading on its own in Kerala, which would classify these populations as invasive by definition,” says Nitya Prakash Mohanty, a Marie-Skłodowska-Curie Postdoctoral Fellow at the Muséum National d’Histoire Naturelle in Paris, France, and a scientist not associated with the study. The population in Kerala could be more widespread than currently recorded.
Without intensive biosecurity at the national or state level, the spread of non-native species into India (and from India) will likely increase.
Mohanty further adds, “Unscreened trade, unlike best practices in countries like New Zealand, will inevitably lead to multiple invasions, though there may be a delay in detection.”