Cosmocercidae (Nematoda) of selected species of amphibians of South Africa

Abstract

Recent studies revealed that parasites outweigh their host species in terms of species richness. This suggests parasitism as the most common lifestyle. In present times, parasites have an even higher species richness and abundance mainly due to host species dispersal, invasion and human activities. Of these, members of the family Cosmocercidae are found globally, most commonly parasitising Anura. These nematodes were found to be one of the most abundant groups of parasites with a wide host range which includes freshwater fish, amphibians, reptiles, with some recorded in birds and mammals. Species of Cosmocercidae are distinguished mainly by the differences in male genital morphology. Numerous inaccurate descriptions, redescriptions and the synonymisation of found species, followed by the lack of male found specimens and molecular data, caused taxonomic uncertainties in this group. Despite the numerous studies and the development of advanced methods and techniques, fauna of cosmocercid nematodes in South Africa is still represented by four species of Aplectana, Railiet and Henry, 1916 and one species of Cosmocerca Diesing, 1861. As a result, the most common species found in many amphibians (and reptiles) throughout South Africa is Cosmocerca ornata (Dujardin, 1845), initially described from the European green (=edible) frog and European common frog in France. This seems unlikely due to the geographical distance and difference in host species. In the present study helminthological material was collected from 193 frog specimens and the nematodes were studied under light microscopes. The morphological and morphometrical data illustrate significant differences between found specimens in comparison to the known species. Morphological differences are also supported by the molecular data of partial 18S and ITS-28S nuclear genes. Species were morphologically different in the number and/or arrangement of papillae from the known species with some resembling Aplectana capensis Baker, 1981 and A. macintoshii Stewart, 1914. These characteristics are used as a common distinguishing feature in species differentiation of cosmocercin nematodes. The number of host species was significantly extended from the known records. Thus, we believe that cosmocercin fauna of South African amphibians are more diverse than previously documented.