Parasite-mediated disruptive selection in a natural Daphnia population
1 W. K. Kellogg Biological Station, Michigan State University, Hickory Corners, MI 49060, USA
2 Department of Zoology, University of Wisconsin, Madison, WI 53706, USA
3 School of Biology, Georgia Institute of Technology, Atlanta, GA 30332-0230, USA
4 School of Biological Sciences, University of Nebraska, Lincoln, NE 68588, USA
5 School of Integrative Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA
6 Department of Biology, Indiana University, Bloomington, IN 47405, USA
7 Division of Environmental Biology, National Science Foundation, Arlington, VA 22230, USA
8 Department of Plant Biology, Michigan State University, East Lansing, MI, USA
BMC Evolutionary Biology 2008, 8:80 doi:10.1186/1471-2148-8-80Published: 7 March 2008
A mismatch has emerged between models and data of host-parasite evolution. Theory readily predicts that parasites can promote host diversity through mechanisms such as disruptive selection. Yet, despite these predictions, empirical evidence for parasite-mediated increases in host diversity remains surprisingly scant.
Here, we document parasite-mediated disruptive selection on a natural Daphnia population during a parasite epidemic. The mean susceptibility of clones collected from the population before and after the epidemic did not differ, but clonal variance and broad-sense heritability of post-epidemic clones were significantly greater, indicating disruptive selection and rapid evolution. A maximum likelihood method that we developed for detecting selection on natural populations also suggests disruptive selection during the epidemic: the distribution of susceptibilities in the population shifted from unimodal prior to the epidemic to bimodal after the epidemic. Interestingly, this same bimodal distribution was retained after a generation of sexual reproduction.
These results provide rare empirical support for parasite-driven increases in host genetic diversity, and suggest that this increase can occur rapidly.