Andrea Pugliese (Universita' di Trento)
00/11/17, 13:30-
at Room No.3631 (6th floor of the 3rd building of the Faculty of Sciences)
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Evolutionary models for macro-parasites are, to a large degree, missing, possibly because of the complexity of the equations describing their dynamics. In this talk I analyse the subject of virulence evolution for macro-parasites assuming, as widely used for micro-parasites since Anderson and May (1982), a trade-off between virulence and parasite fecundity. Starting point is a model consisting of infinitely many equations for the interaction of a host population with two macro-parasite species. These models have been generally been studied through approximations (Dobson, 1985) that do not lend themselves to evolutionary interpretation. On the other hand, I could compute analytically the conditions for invasion of a new strain in the exact infinite model (Pugliese, 2000). Using the invasion conditions, one finds a unique evolutionary stable strategy of intermediate virulence. In reasonable numerical example, it appears that the virulence at the evolutionary stable strategy, though intermediate relative to feasible strategies, is rather high compared with hosts' natural death rate and optimal strategies for micro-parasites. I will consider the effect of parasites' sexual reproduction and of multiple infections on the evolution of virulence. It appears that both these factor reduce noticeably the evolutionary level of virulence, bringing it closer to empirical estimates. In this analysis, the host is assumed to be genetically fixed, so that coevolutionary issues can not be considered. This is certainly a serious drawback, since both organisms can be expected to evolve at similar time-scales. This analysis mainly provides a framework for future work.
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