Evol Ecol Res 11: 1169-1188 (2009)     Full PDF if your library subscribes.

Testing assumptions of the trade-off theory of the evolution of parasite virulence

Jesse L. Brunner1 and James P. Collins2

1Department of Environmental and Forest Biology, SUNY College of Environmental Science and Forestry, Syracuse, New York and  2School of Life Sciences, Arizona State University, Tempe, Arizona, USA

Correspondence: J.L. Brunner, Department of Environmental and Forest Biology, SUNY College of Environmental Science and Forestry, Syracuse, NY 13210, USA.
e-mail: jbrunner@esf.edu

ABSTRACT

Background: Parasite replication is essential for transmission, but is thought to have inevitable virulent effects. The trade-off theory of parasite virulence asserts that parasites balance virulence (the increased death rate of infected hosts), which shortens the infectious period and thus reduces transmission opportunities, against transmissibility (the probability of transmission given a contact) to maximize overall transmission.

Questions: To what extent are virulence and transmissibility parasite traits? Are these traits correlated such that more virulent infections are more transmissible?

Methods: We infected tiger salamander (Ambystoma tigrinum) larvae with nine isolates of the Ambystoma tigrinum virus (ATV) and then exposed naive larvae to these infected larvae, measuring mortality rates in both to test the heritability of virulence. We then exposed five lineages of A. tigrinum larvae to five ATV isolates in a factorial design and measured mortality rates and virus shedding in each host–virus combination to determine the extent to which transmissibility and virulence are traits of the host and parasite, and whether they are related.

Results: Virulence is a heritable trait of virus isolates, but the variation among isolates is swamped by the much larger differences among host lineages. Transmissibility is clearly a viral trait. Within a given host lineage or across host–virus combinations there was little evidence that more virulent infections were also more transmissible. These results do not support the trade-off theory of virulence, but may reflect selection for alternative routes of ATV transmission.

Keywords: evolution of virulence, ranavirus, tiger salamander, trade-off theory, transmissibility.

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        © 2009 Jesse L. Brunner. All EER articles are copyrighted by their authors. All authors endorse, permit and license Evolutionary Ecology Ltd. to grant its subscribing institutions/libraries the copying privileges specified below without additional consideration or payment to them or to Evolutionary Ecology, Ltd. These endorsements, in writing, are on file in the office of Evolutionary Ecology, Ltd. Consult authors for permission to use any portion of their work in derivative works, compilations or to distribute their work in any commercial manner.

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