Does competition affect the distribution of parasites within hosts? Testing for intra- and interspecific competition among intestinal parasites in whitecheek surgeonfish (Acanthurus nigricans) of Kiritimati Island, Northern Line Islands

Background/Question/Methods

Competition is recognized as an important determinant of the distribution of free-living species but its role in shaping parasite communities is uncertain. We assessed the influence of competition on the within-host distribution of parasites, using the intestinal parasite guild of whitecheek surgeonfish (Acanthurus nigricans) collected on Kiritimati Island, a coral atoll of the central equatorial Pacific. We detected a microscaphiid trematode, two species of cucullanid nematode, and an acanthocephalan in the intestines of these hosts, and made a detailed investigation of the response of the most abundant parasite – the trematode – to the presence of potential competitors of the same and different species. 

Results/Conclusions

In general, we observed more trematodes in the posterior of the intestine than in the anterior of the intestine. We observed reduced overall trematode abundance in the presence of potential competitors of other species. Where other species were present, the trematode was distributed differently across the intestinal habitat: in the presence of acanthocephalans, the trematodes were more posteriorly distributed than they were when the trematode occurred alone. These differences could be a consequence of interspecific competition. Our study provides supporting evidence for the potential importance of interspecific interactions in shaping the within-host distribution of intestinal parasites.