Phylogenetic relationships and genetic diversity of Nemesis Risso, 1826 species found on different elasmobranch host species off the KwaZulu-Natal coast, South Africa

Members of the order Siphonostomatoida (Copepoda) are generally poorly described from South African waters. Nemesis is one of 12 genera in the family Eudactylinidae and includes about nine species. In this study, we investigated whether there is any population structure among Nemesis lamna individuals infecting the white shark Carcharodon carcharias and the shortfin mako Isurus oxyrinchus according to host species or capture locality on the KwaZulu-Natal coast, South Africa. Additionally, we estimated the genetic diversity and the phylogenetic relationships among different Nemesis individuals collected from seven elasmobranch host species. Collected specimens were preserved in 70% ethanol and DNA was extracted, whereafter a fragment of the mitochondrial cytochrome oxidase I (COI) gene was amplified. Sequenced polymerase chain reaction products were aligned and analysed. The total dataset consisted of 34 newly generated COI sequences, four GenBank sequences and Eudactylina pusilla as an outgroup. There was no indication of grouping or population structure among the N. lamna individuals in terms of their host species or capture locality. The estimated topologies confirmed the division of Nemesis individuals into a N. lamna group and a Nemesis spp. group consisting of smaller individuals. These smaller Nemesis spp. individuals from five different host species seemed to represent three different species.