Failure to diverge in African Great Lakes: The case of Dolicirroplectanum lacustre gen. nov. comb. nov. (Monogenea,Diplectanidae) infecting latid hosts

Speciation of fish in the African Great Lakes has been widely studied. Surprisingly, extensive speciation in parasites was only recently discovered in these biodiversity hotspots, notably in monogeneans (Platyhelminthes) from Lake Tanganyika. Diplectanum is a monogenean genus of which only a single species is known from the Great Lakes: Diplectanum lacustre (Diplectanidae) living on lates perches (Latidae) of Lake Albert. Despite their primary marine origin, latids have diversified in African freshwaters including several Great Lakes. In better-studied marine diplectanid species, incongruence between morphological and genetic differentiation was documented. As freshwater systems provide more opportunities for speciation than the marine realm, we ask whether diplectanids of Lates spp. of the Great Lakes underwent similar diversification as their hosts. Fresh and museum specimens of five African latid species (Lates angustifrons, L. mariae, L. microlepis, L. niloticus, L. stappersii) were examined for the presence of monogenean gill parasites. Monogeneans were characterised morphologically via morphometrics of sclerotised structures and genetically using nuclear and mitochondrial markers. Continuous morphological variation was documented in these parasites. In addition, the genetic distance, based on the COI region, between parasites of geographically isolated host species did not reach the level typically associated with distinct diplectanid species. Therefore, a single species of a newly described genus, Dolicirroplectanum lacustre gen. nov. comb. nov. is suggested to infect latid species in the examined basins. We discuss this parasite’s failure to diverge in the light of the congruence between the rate of molecular evolution in COI and host historical distribution.