Genomic signals of natural hybridization between Microcebus murinus and M. ravelobensis in northwestern Madagascar

The crossbreeding between individuals of different species can constitute a threat for biodiversity when a species with a narrow distribution range meets a widespread species. In Madagascar, most of the described lemur species are restricted to small areas, but some species with a larger distribution range are known to live in sympatry with microendemic species, as it is the case in the genus Microcebus. So far, only one single case of hybridization, between the two sister species M. murinus and M. griseorufus, was reported in Microcebus. This study aims to investigate whether hybridization may occur between the more distantly related M. murinus and M. ravelobensis in Ankaranfantsika National Park. Genome-wide SNPs from RAD-seq from 28 M. murinus and 78 M. ravelobensis were used to investigate the occurrence of hybridization in two sampling sites within the Park. Clustering analyses based on nuclear data revealed eight individuals with >1% admixed ancestry. A maximum likelihood tree based on the partial COI gene revealed that all introgressed individuals had a mitochondrial haplotype belonging to M. ravelobensis. Our results suggest occasional unidirectional hybridization between female M. ravelobensis and male M. murinus in the two sites. It is likely that male M. murinus dispersed into the areas occupied by M. ravelobensis and successfully mated with M. ravelobensis females. Introgressive hybridization may have played a larger role during the expansion of M. murinus from southwestern Madagascar towards the North than previously thought. Given that M. ravelobensis is classified as Endangered by the IUCN, this process should receive more attention in the future.