Morphological and Genetic Divergence in a Gill Monogenean Parasitizing Distant Cichlid Lineages of Lake Tanganyika: Cichlidogyrus nshomboi (Monogenea: Dactylogyridae) from Representatives of Boulengerochromini and Perissodini

Abstract

As hosts constitute the resource for parasites, an adaptive radiation in a host can drive one in a parasite. In Lake Tanganyika, the diversification of cichlids has often led to a diversification of their Cichlidogyrus monogeneans. Hitherto, Cichlidogyrus nshomboi was known only from Boulengerochromis microlepis, the sole member of Boulengerochromini. Surprisingly, we retrieved this monogenean from Perissodus microlepis, P. straeleni and Haplotaxodon microlepis, belonging to Perissodini. We sequenced the nuclear 18S, 28S, ITS1 rDNA, and the mitochondrial COI genes and studied the morphology of the male copulatory organ (MCO) and the anchors of the attachment organ. This confirmed the conspecificity of the specimens. The occurrence of C. nshomboi on unrelated host lineages could be explained by inheritance from a common ancestor, or by host-switching. We further investigated the genetic and morphological variation across taxonomic (host tribes and species) and geographical scales. Results revealed divergence in ITS1 and COI between parasites infecting different tribes, which could indicate incipient speciation. Additionally, morphological differentiation in the shape and size of anchors was found between these groups, which could be attributed to phenotypic plasticity or to adaptation. Monogeneans from large-bodied B. microlepis had significantly larger anchors, whereas only two of the four measurements differed for the MCO. Unexpectedly, no morphological variation was observed between specimens infecting different species of Perissodini from nearby localities. However, differences were found between C. nshomboi infecting P. microlepis from different parts of the lake, which could be linked to the population genetic structure of the host.