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: <i>Rhabdomys</i> spp., <i>Micaelamys namaquensis</i>, and <i>Otomys unisulcatus</i> 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. <i>Syphacia</i> was the only genus represented by two putatively host-specific species, supported by mtDNA <i>COX1</i> sequencing. This genus was also the most prevalent and abundant within <i>Rhabdomys</i> spp. and <i>M. namaquensis</i>, which each harboured a total of ten nematode species. The genus <i>Nematodirus</i> was the most prevalent and abundant in <i>O. unisulcatus</i>, which harboured five species. Proportionally, the number of heteroxenous species was highest in <i>M. namaquensis</i> (50%), followed by <i>Rhabdomys</i> spp. (30%) and <i>O. unisulcatus</i> (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 <i>Rhabdomys</i> spp. and for <i>O. unisulcatus and</i> five for <i>M. namaquensis</i>. New locality records are provided for five nematode species, and an undescribed species of the genus <i>Gastronodus</i> 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.