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Host and Parasite Counteradaptations: An Example from a Freshwater Snail
Dennis J. Minchella, Bonnie K. Leathers, Kenneth M. Brown and James N. McNair
The American Naturalist
Vol. 126, No. 6 (Dec., 1985), pp. 843-854
Stable URL: http://www.jstor.org/stable/2461259
Page Count: 12
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Host-parasite interactions may lead to a variety of outcomes. Trematode infection of pulmonate snails is often associated with increased growth and/or survivorship of snail hosts. We use the freshwater pulmonate Lymnaea elodes and its trematode parasites to test whether this increase is a parasite adaptation, a host adaptation, or a side effect that serves no adaptive function for either participant. Field experiments indicate that trematode parasitism significantly reduces host fecundity and causes a temporary elevation and subsequent reduction in host growth. A 2-yr field survey of the prevalence of trematode infection in three snail populations revealed a significant positive relationship between shell size and prevalence. Apparently, L. elodes does not outlive its trematode infections. When survey data are compared with theoretical curves generated from a simple model of the system, it appears that trematode parasitism increases the survivorship of infected snails. Overall, the results suggest that increased survivorship in trematode-infected L. elodes is a parasite strategy for providing a stable, longterm resource for the parasite.
The American Naturalist © 1985 The University of Chicago Press