Cichlidogyrus parasitic infection and its potential role in the diversification of its cichlid fish host

Parasites and hosts may engage in arms races, potentially promoting the divergence of host populations exposed to different parasites.
In Lake Victoria, cichlids have undergone adaptive radiation, resulting in a wide ecological. They are infected by Cichlidogyrus, a species-rich genus of monogenean worms that is specific to cichlids and exhibits host specificity in some cichlid lineages.

We investigate the contribution of Cichlidogyrus to Lake Victoria cichlid speciation, by testing: 1) if different host species have different infection profiles, that would emerge from the evolution of specific resistance; 2) for host-parasite co-diversification, as opposed to sorting of ancestral Cichlidogyrus species among newly arisen host, by including a host lineage that is not part of the radiation. We predict a higher worm diversity and abundance in the non-diversified lineage, as it may not have evolved specific resistance.

Cichlidogyrus were isolated from the gills of 6 sympatric endemic cichlid species: the non-diversified A.alluaudi and 5 species of the radiation. Worm morphology was assessed to identify morphospecies.

Infection profiles were similar in all 5 radiating cichlids, inconsistent with parasite-driven diversification. The non-diversified host had more worm individuals and morphospecies. These results suggest that parasite resistance differs between radiating and non-radiating species, but do not support a role of parasites in driving divergence within the radiation.