Mitogenomics, phylogenetic position, and updated distribution of Ergasilus kandti, an ergasilid copepod parasitizing African cichlid fishes

Ergasilidae is a family of globally distributed copepods parasitizing freshwater fishes. Despite their widespread occurrence, their phylogeographic patterns are poorly understood, specifically in the African Great Lakes. Here, we aim to provide an update on the distribution of Ergasilus kandti, a copepod species infecting Tylochromis polylepis, an endemic cichlid fish species in Lake Tanganyika, and the phylogenetic relationship of African ergasilids. We present the first record of E. kandti parasitizing the gills of T. polylepis in Lake Tanganyika proper, identified through light microscopy and, for the first time for any ergasilid, confocal laser scanning microscopy. We suggest that this technique adds spatial context to characters that are hardly visible while using light microscopy. Phylogenetic analyses based on ribosomal DNA fragments suggest two monophyletic groups of African ergasilids. However, the phylogenetic relationships of Ergasilus remain unresolved, possibly because of the insufficient resolution of these widely used phylogenetic markers and low taxonomic coverage. A comparison of ergasilid mitochondrial genomes highlights traits found in other parasite lineages including genome shrinkage and low evolutionary rates of the cox1 gene. This study presents the most extensive molecular characterization of any ergasilid species to date.