The role of parasites in host speciation. Testing for parasite-mediated divergent selection at different stages of speciation in cichlid fish

Parasites represent one of the most successful modes of life in nature and are an important component of ecosystems. By imposing fitness costs on their hosts, parasites constitute a major agent of ecological selection. The host-parasite coevolutionary dynamics of adaptation and counter-adaptation may promote host diversification. The cichlid fish of Lake Victoria have rapidly diversified into hundreds of species, making them a good model system for studying the early stages of speciation. I investigate whether parasites drive or contribute to host speciation by analysing infection patterns in closely related cichlid populations. I found support for two prerequisites for parasite-mediated selection: host species differed in their infection profiles and these infection differences were maintained over multiple sampling years. Different parasites were located in different microhabitats in the fish gills, also depending on the host species. Since microhabitat segregation constitutes another axis of infection heterogeneity, I suggest to include it in future studies. Host species variation in infection was not fully explained by exposure to parasites, suggesting that other intrinsic host properties (i.e. immunity) also play a role. Incipient cichlid species reared in aquaria with uniform parasite exposure did not differ in infection, indicating they have not (yet) evolved differences in immunity. This is inconsistent with a role of parasites in driving host divergence. Infection differences accumulate as hosts become more genetically differentiated, but only reproductive isolated host species display a significant difference in infection. This suggests that parasites may contribute to host divergence but they are not initiating it

The role of parasites in host speciation:Testing for parasite-mediated divergent selection at different stages of speciation in cichlid fish

Parasites represent one of the most successful modes of life in nature and are an important component of ecosystems. By imposing fitness costs on their hosts, parasites constitute a major agent of ecological selection. The host-parasite coevolutionary dynamics of adaptation and counter-adaptation may promote host diversification. The cichlid fish of Lake Victoria have rapidly diversified into hundreds of species, making them a good model system for studying the early stages of speciation. I investigate whether parasites drive or contribute to host speciation by analysing infection patterns in closely related cichlid populations. I found support for two prerequisites for parasite-mediated selection: host species differed in their infection profiles and these infection differences were maintained over multiple sampling years. Different parasites were located in different microhabitats in the fish gills, also depending on the host species. Since microhabitat segregation constitutes another axis of infection heterogeneity, I suggest to include it in future studies. Host species variation in infection was not fully explained by exposure to parasites, suggesting that other intrinsic host properties (i.e. immunity) also play a role. Incipient cichlid species reared in aquaria with uniform parasite exposure did not differ in infection, indicating they have not (yet) evolved differences in immunity. This is inconsistent with a role of parasites in driving host divergence. Infection differences accumulate as hosts become more genetically differentiated, but only reproductive isolated host species display a significant difference in infection. This suggests that parasites may contribute to host divergence but they are not initiating it

Four new species of Cichlidogyrus (Platyhelminthes, Monopisthocotyla, Dactylogyridae) from Lake Victoria haplochromine cichlid fishes, with the redescription of C. bifurcatus and C. longipenis.

African cichlids are model systems for evolutionary studies and host-parasite interactions, because of their adaptive radiations and because they harbour many species of monogenean parasites with high host-specificity. Five locations were sampled in southern Lake Victoria: gill-infecting monogeneans were surveyed from 18 cichlid species belonging to this radiation superflock and two others representing two older and distantly related lineages. We found one species of Gyrodactylidae, Gyrodactylus sturmbaueri Vanhove, Snoeks, Volckaert & Huyse, 2011, and seven species of Dactylogyridae. Four are described herein: Cichlidogyrus pseudodossoui n. sp., Cichlidogyrus nyanza n. sp., Cichlidogyrus furu n. sp., and Cichlidogyrus vetusmolendarius n. sp. Another Cichlidogyrus species is reported but not formally described (low number of specimens, morphological similarity with C. furu n. sp.). Two other species are redescribed: C. bifurcatus Paperna, 1960 and C. longipenis Paperna & Thurston, 1969. Our results confirm that the monogenean fauna of Victorian littoral cichlids displays lower species richness and lower host-specificity than that of Lake Tanganyika littoral cichlids. In C. furu n. sp., hooks V are clearly longer than the others, highlighting the need to re-evaluate the current classification system that considers hook pairs III-VII as rather uniform. Some morphological features of C. bifurcatus, C. longipenis, and C. nyanza n. sp. suggest that these are closely related to congeners that infect other haplochromines. Morphological traits indicate that representatives of Cichlidogyrus colonised Lake Victoria haplochromines or their ancestors at least twice, which is in line with the Lake Victoria superflock being colonised by two cichlid tribes (Haplochromini and Oreochromini)

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