Evolution of trophic transmission in parasites: Why add intermediate hosts?

American Naturalist
By: , and 



Although multihost complex life cycles (CLCs) are common in several distantly related groups of parasites, their evolution remains poorly understood. In this article, we argue that under particular circumstances, adding a second host to a single-host life cycle is likely to enhance transmission (i.e., reaching the target host). For instance, in several situations, the propagules of a parasite exploiting a predator species will achieve a higher host-finding success by encysting in a prey of the target predator than by other dispersal modes. In such a case, selection should favor the transition from a singleto a two-host life cycle that includes the prey species as an intermediate host. We use an optimality model to explore this idea, and we discuss it in relation to dispersal strategies known among free-living species, especially animal dispersal. The model found that selection favored a complex life cycle only if intermediate hosts were more abundant than definitive hosts. The selective value of a complex life cycle increased with predation rates by definitive hosts on intermediate hosts. In exploring trade-offs between transmission strategies, we found that more costly trade-offs made it more difficult to evolve a CLC while less costly trade-offs between traits could favor a mixed strategy.

Publication type Article
Publication Subtype Journal Article
Title Evolution of trophic transmission in parasites: Why add intermediate hosts?
Series title American Naturalist
DOI 10.1086/375681
Volume 162
Issue 2
Year Published 2003
Language English
Publisher The University of Chicago Press
Contributing office(s) Western Ecological Research Center
Description 10 p.
First page 172
Last page 181
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