Chattopadhyay, B. | Search bioRxiv

bioRxiv2021

Historical climate change and megafaunal extinctions linked to genetic diversity declines in shorebirds

Understanding the relative contributions of historical and anthropogenic factors to declines in genetic diversity is important for informing conservation action. Using genome-wide DNA of fresh and historic specimens, including that of two species widely thought to be extinct, we investigated fluctuations in genetic diversity and present the first complete phylogenomic tree for all nine species of the threatened shorebird genus Numenius, known as whimbrels and curlews. Most species faced sharp declines in effective population size, a proxy for genetic diversity, soon after the Last Glacial Maximum (around 20,000 years ago). These declines occurred prior to the Anthropocene and in spite of an increase in breeding area predicted by environmental niche modelling, suggesting that they were not caused by climatic or recent anthropogenic factors. Crucially, these genetic diversity declines coincide with mass extinctions of mammalian megafauna in the Northern Hemisphere. Demise of ecosystem-engineering megafauna which maintained open habitats would have been detrimental for grassland and tundra-breeding Numenius shorebirds. Our work suggests that the impact of historical factors such as megafaunal extinction may have had wider repercussions on present-day population dynamics of open habitat biota than previously appreciated.

evolutionary biology↗

bioRxiv2020

Western Ghats Myrtaceae are not Gondwana elements but likely dispersed from south-east Asia

Gondwana break-up is one of the key sculptors of the global biogeographic pattern including Indian subcontinent. Myrtaceae, a Gondwana family, demonstrates a high diversity across Indian Western Ghats. A rich paleo-records in Deccan Intertrappean bed in India strive to reconcile two contending hypothesis of origin and diversification of Myrtaceae in India, namely Gondwana elements floated on peninsular India or lineages invading from south-east Asia. In this study, we have reconstructed the biogeographic history of Myrtaceae of Western Ghats of India combining fossil-calibrated phylogeny, ancestral area reconstruction, and comparing various dispersal models. Phylogenetic reconstructions divided lineages into multiple clades at the tribal level that mostly is in agreement with previous descriptions. Dated tree indicated a presumable Gondwanan origin of Myrtaceae (95.7 Ma). The Western Ghats taxa are relatively younger and seem to have arrived either through long-distance oceanic dispersal in middle Eocene (Rhodomyrtus tomentosa), and Miocene (Eugenia) or through major overland dispersals throughout Miocene (Syzygium). However, late Cretaceous fossilsin India lends support to the existence of proto-Myrtaceae on floating peninsular India. Taken together, we conclude that Myrtaceae lineages on the biotic ferry were perhaps extirpated by Deccan volcanism leaving a little or no trace of living Gondwanan link, while the Western Ghats was likely enriched by dispersed elements either from south-east Asia or from South America.

genomics↗