Museum phylogenomics of extinct Oryctes beetles from the Mascarene Islands

The evolution of island systems is characterized by processes that result in extreme morphological diversity and high endemism. Therefore, the phylogeny of island species is often difficult to reconcile, i.e. the flightless dodo from Mauritius was assigned to the family of doves only through DNA analysis of subfossils. On islands, many insect species have gone extinct through habitat loss, but historical specimens have not been harnessed for phylogenomic reconstructions. Here, we employed historical museum specimens from the Mascarene Islands to generate the first whole-genome based phylogeny of three presumably extinct species of the rhinoceros beetle genus Oryctes. We compared their genomes with those of an extant Oryctes species from Réunion, as well as a flightless Réunion-based species previously placed into the supposedly unrelated genus Marronus. We found that Marronus borbonicus belongs instead to the genus Oryctes and that the two Réunion-based species (O. borbonicus and M. borbonicus) are not sister taxa, suggesting two independent invasions. The divergence time between them (<3Myr) overlaps with the volcanic formation of Réunion, likely indicating that M. borbonicus became flightless in situ. Our study showcases the power of genomes from insect museum specimens to address phylogenetic questions in light of skyrocketing extinction rates. Preprint doi: https://doi.org/10.1101/2020.02.19.954339