Examination of parasite guilds in the hindgut of the American Giant Millipede, Narceus americanus

Student: Meg Deeter
Mentor: Ramon Carreno (Department of Zoology)

It is not uncommon for host organisms to be concurrently infected with multiple species of parasites. One example exists within the hindgut of the American giant millipede, Narceus americanus. The hindgut houses a microcommunity of symbionts that includes a variety of parasitic nematodes. Interestingly enough, it appears that different parasite species aggregate within the hindgut tandem to one another in predictable portions of the hindgut. This may be due to resource partitioning along the hindgut. The primary objective of our study was to quantify the diversity and distribution patterns of these parasites. 

The distribution of pinworm species (Nematoda: Oxyurida) within arthropod host organisms is not well documented, particularly in those that harbor multiple parasite species concurrently. Individual American giant millipedes, Narceus americanus, are model organisms towards understanding parasite distribution patterns, as they simultaneously harbor 2 distinctive species of pinworm, Aorurus agile and Thelastoma spp. in their hindguts. Additionally, N. americanus also yields large populations of Rhigonema spp. (Nematoda: Rhigonematidae) in the anterior end of the hindgut. The lower intestinal tracts from N. americanus individuals (n=98) were dissected in the posterior-to-anterior direction in 5 mm increments. With each increment, the prevalence of each type of nematode was recorded. Nematodes were collected and preserved following each dissection’s completion. Preliminary data show Aorurus agile to span the entirety of the hindgut, whereas Thelastoma spp. are more likely to aggregate in the medial region of the hindgut. Rhigonema spp. are almost exclusively found within 10 mm of the pylorus, the valve connecting the mid- and hindgut regions. Our results support the existence of realized niches for parasitic nematodes occupying N. americanus.