Diversity and distribution of gastrointestinal nematodes in three sympatric rodent taxa from South Africa

Nematodes are common internal parasites of rodents but information on their diversity and abundance remains limited. This study aimed to document the nematode diversity associated with three sympatric rodent taxa: Rhabdomys spp., Micaelamys namaquensis , and Otomys unisulcatus distributed across the Fynbos, Succulent Karoo, and Nama-Karoo biomes of the Western Cape, South Africa. Rodents (n = 576) were trapped at 12 localities between 2023 and 2025. Fifteen morphologically distinguishable nematode species, representing 14 genera, were microscopically identified from the gastrointestinal tracts of the rodents. Syphacia was the only genus represented by two putatively host-specific species, supported by mtDNA COX1 sequencing. This genus was also the most prevalent and abundant within Rhabdomys spp. and M. namaquensis , which each harboured a total of ten nematode species. The genus Nematodirus was the most prevalent and abundant in O. unisulcatus , which harboured five species. Proportionally, the number of heteroxenous species was highest in M. namaquensis (50%), followed by Rhabdomys spp. (30%) and O. unisulcatus (20%). Monoxenous species were on average more widely distributed compared to heteroxenous species. No consistent biome pattern was observed for the individual nematode species, though heteroxenous species appeared to be more common in the xeric Nama-Karoo compared to the more mesic Fynbos biome. Overall, three new nematode-host associations were recorded for Rhabdomys spp. and for O. unisulcatus and five for M. namaquensis . New locality records are provided for five nematode species, and an undescribed species of the genus Gastronodus was discovered. This study highlights the largely unexplored nematode diversity associated with rodents in South Africa and underscores the importance of host identity and environmental context in shaping nematode diversity and distribution. • 15 putative nematode species present in three sympatric rodent taxa. • Heteroxenous species are proportionally more abundant in omnivorous rodents. • Novel locality records and host-parasite associations noted. • Two host-specific Syphacia lineages were supported by morphology and mtDNA. • Larger number of heteroxenous species recorded in xeric biomes.