Phylogenetic reconstruction of African weakly electric fish (Campylomormyrus spp.) is suggestive of ancient introgression events.

The African weakly electric fish genus Campylomormyrus belongs to the species-rich family Mormyridae and comprises 15 described species. Previous species trees that focus on the genus, have included at most ten species. The resulting phylogenies have been used to explain the evolution of the species-specific electrical organ discharge (EOD) and interpreted in the context of sympatric speciation caused by disruptive selection. However, available molecular phylogenies that are focused on the Campylomormyrus genus rely only on a limited number of genetic markers. Here, we used ddRAD sequencing to genotype 65 individuals from twelve Campylomormyrus species and Gnathonemus petersii at more than 8,000 SNPs. We reconstruct a robust species tree that is suggestive of ancient introgression events between different species, which might affect both genetic and trait variability in the genus. Different levels of genetic and EOD diversity in two significant Campylomormyrus clades reveals that i) certain species might be in early stages of their speciation process, ii) that hybridization/introgression occurs in mormyrids and iii) that EOD-related genes could be potential speciation genes. Our genomic approach demonstrates the significance of these findings in understanding the evolution of Campylomormyrus.