Divergent resistance to a monogenean flatworm among three-spined stickleback populations

Abstract

1.Given their ubiquity, we might expect parasites to play an important role in the adaptive divergence of host populations. Specifically, adaptation to local parasite communities is predicted to influence the evolution of a number of host traits such as parasite resistance. 2.To investigate the possibility that divergent parasite-mediated selection drives population-level variation in parasite resistance, we artificially infected lab-reared three-spined sticklebacks with the monogenean flatworm Gyrodactylus gasterostei. The fish were derived from five populations from North Uist, Scotland, that were chosen because they differed in natural infection levels of Gyrodactylus arcuatus. 3.We found substantial differences in resistance to G. gasterostei among populations. Resistance was defined largely by the ability to limit the size of the worm population rather than by the timing of the host response. 4.Experimental resistance was not significantly correlated with natural infection levels of G. arcuatus. However, in general, populations with greater exposure to G. arcuatus were shown to be more resistant to G. gasterostei. Fish from the only naturally unexposed population showed the highest susceptibility, which may be the result of less selection to maintain resistance. 5.Taken together, these results suggest that the divergent selection mediated by Gyrodactylus may play a role in driving population-level variation in resistance to this parasite. © 2010 The Authors. Functional Ecology © 2010 British Ecological Society.