Ecological conditions that favor the evolution of intermediate-virulence in an environmentally transmitted parasite |
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Authors: | Michael Golinski Ernest Barany Mary Ballyk |
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Institution: | (1) Department of Biology, New Mexico State University, Las Cruces, NM 88003, USA;(2) Department of Mathematical Sciences, New Mexico State University, Las Cruces, NM 88003, USA |
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Abstract: | In this paper we develop and analyze several populaion-dynamic models of an environmentally transmitted symbiotic parasite
infecting an isolated population of susceptible hosts. In our most basic model infection acts only to decrease the average
lifetime of the infected host, parasites are only transmitted to uninfected hosts, there is no recovery from infection, and
the rate of parasite transmission is an increasing function of the level of parasite virulence. It is shown that invasion
of the parasite-free equilibrium cannot occur for virulence levels that are either too high or too low. We then incorporate
a number of modifications to the model, among them the possibility that host fertility is reduced by infection, and that transmission
rate depends additionally on susceptible host density. It is shown that the essential nature of the conditions for invasion
are preserved. Thus, natural selection for intermediate virulence is a generic property of a broad class of population models. |
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Keywords: | Free living parasite Intermediate virulence hypothesis Environmental transmission |
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