Diversity and community structure of gastrointestinal helminths of Rhabdomys spp. and other small mammals in South Africa

[摘要] ENGLISH ABSTRACT: Descriptive information forms the basis for broader ecological questions and therefore plays a vital role in studies that explore patterns in parasite diversity, distribution and species assemblages. Parasite-locality information can further aid in the development of species distribution maps that can be of value in the identification of disease risk and aid proactive disease management. As yet, current knowledge of helminth-host and helminth-locality associations in small mammals in South and southern Africa are scant. As a result, it is uncertain how host and environmental factors shape helminth infections and community structure across a climatically diverse landscape. To address this paucity of information the study aims to: (1) record descriptive information on helminth-host associations and the spatial and temporal distribution of helminth parasites associated with small mammals, (2) using two closely related murid hosts, Rhabdomys pumilio (Sparrman) and Rhabdomys dilectus (de Winton), as models, to investigate if between-host species differences in helminth infections are mainly caused by level of sociality (social R. pumilio and solitary R. dilectus) or environmental conditions (more xeric R. pumilio and more mesic R. dilectus), (3) investigate the effect of social and spatial behaviour, of R. pumilio and R. dilectus, on parasite community organization with reference to species co-occurrence and nestedness and (4) explore factors responsible for patterns in similarity in helminth species composition in R. pumilio and R. dilectus. In total 168433 specimens, comprising 56 helminth taxa were recovered from at least 16 rodent, and sengi and shrew species (n = 1079). The helminth species represented 26 genera of which 16 were nematodes, nine cestodes and one acanthocephalan. Overall, the most abundant helminth species was the nematode Heligmonina spira (133.8 ± 13.5), which was also the most prevalent (26.1%). Rhabdomys dilectus harboured 19 nematode and 7 cestode species while R. pumilio harboured 10 nematode and 5 cestode species. Seven helminth species (4 nematodes and 3 cestodes), were shared between the two rodent species, however, they also harboured their own specific helminths.In general, monoxenous (direct life cycle) nematodes were present in higher abundance compared to heteroxenous (indirect life cycle) nematodes and cestodes. Several novel helminth-host and helminth-locality records, in addition to several potentially new helminth species were noted. Life cycle-specific geographic distributions were recorded for monoxenous and heteroxenous nematodes. Helminth infections varied spatially and seasonally with significantly higher helminth abundance and prevalence in the months following the wet season. Cestode infection as well as nematode abundance, species richness or prevalence did not differ between R. dilectus and R. pumilio in between-host species comparisons. However, incidence of nematode infection was significantly higher in R. dilectus than in R. pumilio. Within-host species comparison showed that nematode abundance and species richness in infracommunities of R. pumilio inhabiting the relatively more xeric Karoo biome were significantly lower than in those inhabiting the relatively less xeric Fynbos biome. General patterns of helminth co-occurrence were similar (positive) in the two hosts, but the strength of positive associations increased with an increase in the mean number of helminth species in R. dilectus and in prevalence of infection in R. pumilio. The two host species differed in the relative frequency of positive and negative pairwise species co-occurrences (only positive in R. dilectus and both positive and negative in R. pumilio). Nestedness-related patterns in helminth infracommunities were only found in R. pumilio (predominantly anti-nested), whereas the opposite was the case for their component communities (only nested in R. dilectus). The level of infection was generally associated with the manifestation of non-randomness in helminth assemblages. Although species composition of infracommunities largely overlapped between R. dilectus and R. pumilio they were still significantly different between the two species. In both rodent species helminth infracommunities were more similar among individuals from the same locality than among localities or biomes. This pattern was more distinct for R. dilectus, which may be attributed to larger spatial distribution. Also, helminth species composition among localities correlated significantly negatively with geographic distance between localities, with a higher rate of decrease of similarity of helminth assemblages with an increase in geographic distance in R. pumilio than in R. dilectus.It is evident that spatial variation in helminth infections and community structure of helminth assemblage are dependent on a complex interplay of host and parasite related factors, compounded by environmental variation.

[发布机构] Stellenbosch University