Fine-scale association between parasites and sex in Potamopyrgus antipodarum within a New Zealand lake

Why sexual reproduction is so common despite major costs remains a widely debated evolutionary question. One of the most plausible potential explanations is the Red Queen hypothesis, which proposes that coevolving parasites can generate a selective advantage for sex. This hypothesis predicts that sexual reproduction should be most common where individuals experience a relatively high risk of parasitic infection. Here, we test this prediction at a very fine spatial scale by evaluating whether variation in the frequency of infection by sterilising trematode parasites within a single New Zealand lake population is positively associated with similar variation in the relative frequency of sexually vs. asexually reproducing Potamopyrgus antipodarum, a native New Zealand snail. We found that sexual snails were significantly more common in sites within the lake that were subject to a higher frequency of parasite infection, consistent with the prediction of the Red Queen hypothesis. This result extends previous research on the connection between sexual reproduction and infection in P. antipodarum to a new lake and a finer spatial scale than previously documented.