Foraging networks influence the parasite community of the eastern chipmunk (Tamias striatus)

Background/Question/Methods

Parasite infection depends initially on the host being exposed to an infective stage and yet the likelihood of this exposure event varies greatly between individual hosts. Indeed, the overarching hypothesis in parasite ecology is that variation in infection levels with parasites like helminths can generally be accounted for by variation in susceptibility and exposure; yet hypotheses regarding variation in exposure have not been investigated in detail.  A major challenge in disease ecology is to quantify exposure and identify the behavioral factors that shape it, including social behavior, sexual behavior and foraging behavior.  In this study, we examined the role of foraging behavior on parasite transmission using network techniques to infer how an ecological contact network influenced the exposure and subsequent transmission of parasites in natural populations of eastern chipmunks (Tamias striatus).  We hypothesized that shared foraging space increases transmission of fecal-oral transmitted parasites and tested the prediction that foraging interactions, measured via network edges defined by parasite transmission mode, positively correlate with infection.

Results/Conclusions

The between-host interactions that result from where hosts forage, in relation to other hosts, had a strong positive correlation to infection with parasites that are directly transmitted. This correlation was only present when the definition of a network edge corresponded to the transmission route; there was no correlation between host foraging interactions and infection with indirectly transmitted parasites that require an intermediate host for transmission. In addition, greater degrees of contact in the foraging network predicted the richness of an individual’s intestinal parasite community.  We were able to precisely define infectious interactions in a system where exposure could be examined through foraging and feeding behaviors that reflect the transmission of an endemic community of parasites.  Defining the appropriate measure for exposure is strongly dependent on an understanding of the transmission mode of the parasite(s) of interest and, more generally, a specific and biologically meaningful edge definition is necessary when applying network theory to ecological systems.  Within-host processes, at the interaction of hosts and parasites, will always remain a key to the infection and transmission process, but this study highlights how an understanding of host-host and host-environment interactions that determine exposure to, and spread of, parasite infectious stages is necessary for fuller understanding of host-parasite dynamics.