Understanding susceptibility to extinction using historical museum specimens as a genetic time series

SémIdeev
 13/06/2025
 12:00:00
 Samuel Gornard, MNHN
 IDEEV - Salle Rosalind Franklin

The world faces its sixth mass extinction, caused by global changes linked to human activities. Regarding this threat, not all taxa are equal: some ecological traits could be linked to susceptibility to extinction, such as small geographical range or habitat breadth. Similarly, in insular ecosystems, older taxa appear to be at a higher risk of extinction too. However, it is usually difficult to disentangle the relative role of anthropogenic versus natural factors in causing species to be rare and at risk of extinction. Population genetics can cast light on this problem by detecting selection pressures shaping the genomes of endangered species. However, such studies often lack both comparative and temporal perspectives. In this regard, the Mascarene archipelago represents a striking model for studying the impacts of anthropogenic changes on the susceptibility of species to extinction. Indeed, historical and paleontological records show that these islands were devoid of human presence up until the 17th century. The impact of recent human arrival on Mauritius has been unusually severe, with pristine native forest reduced by 98%, alongside the extinction of 30 to 57% of the vertebrate fauna. Thus, our study focuses on two closely related species of birds from Mauritius, Zosterops mauritianus (Mauritius grey White-eye) and Zosterops chloronothos (Mauritius olive White-eye). While the former is commonly found throughout the whole island, the other is critically endangered, according to the IUCN, and only naturally found is a small area of remaining native forest. We hypothesize that the former species has remained common due to adaptation through natural selection, while the rarer species could not, and therefore declined. Using both museum and modern samples, we built a genetic time-series to test for traces of selection in the genome of both species and sought to compare them.