Contrasting host-parasite population structure and role of host specificity: Morphology and mitogenomics of a parasitic flatworm on pelagic deepwater cichlid fishes from Lake Tanganyika

Abstract

Little phylogeographic structure is presumed for highly mobile species in pelagic zones. Lake Tanganyika is a unique ecosystem with a speciose and largely endemic fauna famous for its remarkable evolutionary history. In bathybatine cichlid fishes, the pattern of lake-wide population differentiation differs among species. We tested the magnifying glass hypothesis for their parasitic flatworm Cichlidogyrus casuarinus. Lake-wide population structure of C. casuarinus ex Hemibates stenosoma was assessed based on a portion of the mtCOI gene combined with morphological characterisation. Additionally, intraspecific mitogenomic variation among 80 individuals within one spatially constrained parasite metapopulation sample was assessed using shotgun NGS. While no clear geographic genetic structure was detected in parasites, both geographic and host-related phenotypic variation was apparent. The incongruence with the genetic north-south gradient observed in the host may be explained by the broad host range of this flatworm as some of its other host species previously showed no lake-wide restriction of gene flow. Our results are consistent with host driven morphological variation without genetic differentiation of the parasite, and highlight the importance of integratively approaching parasites`parasites`potential as "tags" for their hosts. We present the first parasite mitogenome from Lake Tanganyika and propose a methodological framework for studying intraspecific mitogenomic variation of dactylogyrid monogeneans.