Taxonomic status of trichodina heterodentata Duncan, 1977 (Ciliophora: Peritrichia) using standard morphology, as well as molecular techniques

[摘要] English: The family Trichodinidae Raabe, 1959 (Ciliophora, Peritrichia) consists of 11 genera, of which the cosmopolitan genus Trichodina Ehrenberg, 1838 has the largest number of species. A substantial majority of trichodinid species are associated with marine and freshwater fish hosts, while some are also found associated with amphibians, as well as a variety of invertebrate hosts. Some trichodinid species show high levels of host specificity, whilst others occur on a range of hosts. Trichodina heterodentata Duncan, 1977 was first described from fish breeding farms in the Philippines as ectoparasites of imported cichlids, more specifically the Mozambique tilapia from southern Africa, Oreochromis mossambicus (Peters 1885), from the Limpopo River System. Trichodina heterodentata has subsequently been described from Europe, Australia, India, China, South America and Africa, however, it has not yet been found in North America. This cosmopolitan species, with a seeming preference for cichlid hosts, has unambiguous morphological features, but with distinct variances between and within populations. Most fish species harbouring T. heterodentata display multi-trichodinid infestations, however, on its amphibian host, T. heterodentata occurs as a single infestation, which makes it perfect for using it as a model species. After reviewing previous descriptions from North American trichodinids, analysing the morphological data (both from literature along with type material obtained from the Smithsonian Museum) and investigating the distribution patterns of the southern African introduced O. mossambicus throughout North American water systems, it seems likely that Trichodina hypsilepis Wellborn, 1967, is a synonym of T. heterodentata. This not only delegates several North American trichodinid species into synonymy, but also probably indicate an insidious African alien introduction sneaking it way into this continent. Morphological analysis of T. heterodentata, shows that this species is highly variable in regards to its denticle structure, which leads one to wonder if it's might be a species complex, or indeed a single species. Trichodinid taxonomic work to date has primarily focused on morphological characteristics together with host and distribution records. With the advent of modern biochemical laboratory procedures, more and more emphasis is placed on molecular techniques in all fields of taxonomy, especially in parasitology. However, little molecular taxonomy work has been done on trichodinids. Trichodinid specimens were obtained from six different isolated host tadpole (Schlerophrys spp.) populations on the Nxamasere Flood plains, Okavango Panhandle, Botswana. This dissertation will represent the first study in southern Africa to successfully isolate genomic DNA from mobiline symbiotic ciliophorans. Genomic DNA was isolated from T. heterodentata and the 18S rDNA gene was amplified by PCR. After Sanger sequencing a complete phylogenetic tree of all available trichodinid sequences were constructed. All results indicate that trichodinids collected from tadpole hosts in the Okavango Delta are not T. heterodentata, but rather T. hypsilepis, supporting the theory that T. heterodentata, as it is known to date, is a species complex.

[发布机构] University of the Free State