Extensive hybridisation throughout clownfishes evolutionary history

ABSTRACT The contribution of hybridisation in the generation of global species diversity has long been controversial among evolutionary biologists. However, it is now increasingly accepted that hybridisation has many impacts on the process of speciation. Notably, it is an important mechanism fostering adaptive radiation since it can generate new phenotypic combinations enabling the occupancy of new niches. Here, we focused on clownfish (Pomacentridae), a clade of 28 coral reef fishes displaying a mutualistic interaction with sea anemones. This behaviour is the key innovation that triggered adaptive radiation of clownfishes, as each species is able to occupy a different combination of host anemone species and habitat. Previous work suggested that hybridisation might be responsible for the extant diversity of clownfish species. To test this hypothesis, we analysed whole-genome datasets for each clownfish species. First, we reconstructed the phylogeny of the clade based on topology weighting methods, which enables the visualisation of the relationships between taxa across the genome. Then, we highlighted possible ancient hybridisation events based on a comparative genomic framework for detecting introgression in genomes. The resulting phylogeny is consistent with previous works based on a few mitochondrial and nuclear genes, and shallow nodes are now well supported in contrast to past studies. Furthermore, we detected multiple past hybridisation events throughout the evolutionary history of clownfishes, corroborating the potential role of hybridisation in the clownfish adaptive radiation. This study adds to the growing number of studies investigating the genomic mechanisms behind species diversification, drawing us closer to understanding how Earth biodiversity is generated.