Discovery of a free-living nematode phylogenetically related to vertebrate parasites of the genus Strongyloides (Nematoda : Strongyloidoidea): morphological, anatomical and molecular characterisation

Abstract

Nematodes are important, largely because they frequently act as parasites and threaten the health of plants, animals and even humans. Here, we describe an interesting free-living nematode from land snails on Luofu Mountain, Guangdong, China. Alloionema luofuensis, sp. nov. is phylogenetically related to slug-parasite A. appendiculatum and the well-known vertebrate parasites Strongyloides spp. based on small subunit (SSU) and the D2-D3 domain of large subunit (LSU) rDNA sequences. The new species possesses an extremely transparent body and is easily maintained using C. elegans culture media, suggesting a possible application prospect of this free-living nematode as a comparative model system for its related parasites. Morphology and anatomy of the gonochoristic A. luofuensis, sp. nov. adult were described and illustrated. The species is characterised by a filiform tail bisexually, ‘rhabditiform’ oesophagus and ‘rhabditid-like’ female anatomy, but its male caudal region is completely different from that of typical rhabditid nematodes, being absent from an enveloping bursa. It is the first marker taxon characterised morphologically as well as molecularly from the family Alloionematidae, a group of nematodes with hyperdiverse molecular genetic variations underlying highly conserved anatomy. Further molecular and genetic studies on A. luofuensis, sp. nov. populations hold promise to provide insight into evolution of the clade consisting of vertebrate parasites of the heterogonic nematode genus Strongyloides. This is because of its unusual high levels of heterozygosity maintained by the conserved rRNA genes of partial SSU and the D2-D3 domain of LSU for the type isolate of this species.