Evol Ecol Res 4: 219-226 (2002) Full PDF if your library subscribes.
Temporal and spatial distributions of parasites and sex in a freshwater snail
Curtis M. Lively1* and Jukka Jokela2
1Department of Biology, Indiana University, Bloomington, IN 47405-3700, USA and 2Department of Biology, University of Oulu, FIN-90014, Finland
Author to whom all correspondence should be addressed.
The Red Queen hypothesis predicts that sexual reproduction should be favoured in geographic locations where the risk of infection is high. We surveyed 20 lakes on the South Island of New Zealand to determine whether an association exists between the presence of individuals sterilized by trematode larvae and the presence of males in a common freshwater snail (Potamopyrgus antipodarum). The snail is unique in that populations are often mixtures of triploid asexual females that reproduce by apomictic parthenogenesis and diploid sexual individuals that reproduce by cross-fertilization. We compared the results to a similar study conducted over 10 years ago. The results showed a highly significant correlation between the frequency of males in the past and present data. In addition, the results showed a strong significant correlation between the prevalence of trematodes in past and present data sets, indicating that any selection imposed by the parasites has remained reasonably constant. Finally, the frequency of males averaged over both data sets was significantly and positively correlated with the mean frequency of infected individuals. These results suggest that infection levels and male frequency may be relatively stable and that parasites may be a factor in selecting for sexual reproduction.
Keywords: Microphallus, New Zealand, Potamopyrgus antipodarum, Red Queen hypothesis, sexual reproduction.
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