Geographic variation in sterilizing parasite species and the Red Queen

Abstract

The Red Queen hypothesis predicts that sexual reproduction should be favoured in locations where the risk of infection by virulent parasites is consistently high. When hosts are exposed to multiple parasites over their geographic range, the coevolving parasite species may vary among host populations. We surveyed 26 streams on the South Island of New Zealand to determine whether the frequency of snails (Potamopyrgus antipodarum) infected by various sterilizing trematode parasite species was correlated with the frequency of sexual individuals. We compared the results with a survey conducted over 20 years ago to determine whether the associations were consistent. We also evaluated different measures of parasite-mediated selection among populations, including prevalence of the most common local parasite (MCLP) species and parasite diversity to assess the best predictor of sexual reproduction among stream populations. The results showed that the relationship between male frequency and parasite infection is more geographically widespread than previously recorded. Additionally, we found that the prevalence of the MCLP was the best predictor of sex in habitats where hosts populations are infected with multiple parasites (approximately 15 trematode species). This study provides evidence that sexual snails occur more often in environments with high infection levels, and that the pattern of parasiteimposed selection is geographically variable. Support for the Red Queen may be strengthened by focussing on the MCLP, which may vary among host populations.

Parasites, Sex, and Clonal Diversity in Natural Snail Populations

“…Consistent with previous work (e.g., Lively and Jokela 2002;King and Lively 2009), we found that the frequency of sexual individuals increased with the prevalence of infection (Fig. 1A).…”

“…The frequency of infection with the most common parasite was highly correlated with infection by all parasite species (Pearson correlation: r = 0.932, P < 0.001). However, in a previous study examining various measures of parasite-mediated selection, the frequency of the most common local parasite species was found to be the most appropriate (King and Lively 2009). Therefore, we used the infection frequency of the common parasite for all analyses.…”

The ecology of sexual reproduction

“…In addition, recent biogeographical studies of this snail have been consistent with earlier work, suggesting that asexual forms of the snail are more likely to occur in lakes and streams where parasites are rare (Lively, ; Lively & Jokela, ; King & Lively, ; King et al ., ). This pattern could, of course, be generated if males or sexual snails are, in general, inherently more susceptible to infection, but this is not the case (Vergara et al ., ).…”

Higher parasite resistance in Daphnia populations with recent epidemics

“…, 2006; Hasu et al. , 2009; King & Lively, 2009). In particular, whether spatial variation in infection frequency is because of environmental factors, genetic variation for host resistance or a combination of both factors is still unresolved.…”