Gill monogeneans of ‘Gnathochromis’ and Limnochromis (Teleostei, Cichlidae) in Burundi: do the parasites mirror host ecology and phylogenetic history?

Monogenea is one of the most species-rich groups of parasitic flatworms. Research on this taxon in Africa has been recently intensified. For example, already more than 100 nominal species belong to Cichlidogyrus, a genus mostly occurring on cichlids. Twenty-two of these were described from Lake Tanganyika which is a biodiversity hotspot in which many vertebrate and invertebrate taxa underwent unique evolutionary radiations. Parasites were also used as a potential tool to uncover host species relationships. This study presents the first investigation of the monogenean fauna occurring on the gills of endemic Gnathochromis species along the Burundese coastlines. We test whether their monogenean fauna reflects the different phylogenetic position and ecological niche of ‘G.’ pfefferi and G. permaxillaris. Worms collected from specimens of Limnochromis auritus, a cichlid belonging to the same tribe as G. permaxillaris, were used for comparison. Morphological as well as genetic characterisation was used for parasite identification. In total, all 73 Cichlidogyrus individuals collected from ‘G.’ pfefferi were identified as C. irenae. This is the only representative of Cichlidogyrus previously described from ‘G.’ pfefferi, its type host. Gnathochromis permaxillaris is infected by a species of Cichlidogyrus morphologically very similar to C. gillardinae. The monogenean species collected from L. auritus is considered as new for science, but sufficient specimens lack for a formal description. Our results confirm previous suggestions about ‘G.’ pfefferi as a good disperser infected by a single monogenean species. Although G. permaxillaris and L. auritus are placed in the same tribe, there is closer morphological similarity between species of Cichlidogyrus occurring on G. permaxillaris and C. irenae from ‘G.’ pfefferi, compared to the monogeneans of L. auritus. This pattern therefore can be caused by various processes in the parasite-host system’s evolutionary history, such as hostswitching or duplication events. Additional samples, allowing phylogenetic analysis, from the species of Cichlidogyrus occurring on G. permaxillaris and L. auritus are needed to reveal their history.