Parasites tend to track common host genotypes, and according to the Red Queen Hypothesis, this should provide an advantage to hosts that reproduce sexually over asexually since genetic recombination will continuously create new or rare genotypes. One prediction that arises from this hypothesis is that the frequency of sexual reproduction and infection will be negatively correlated—with asexual populations generally experiencing greater parasitism loads. However, in the many decades of research on the Red Queen hypothesis, studies have tested this prediction across a broad diversity of ecological and taxonomic scales—from comparisons among populations within a species, to between related species, and even among host communities that vary in richness and diversity. Here we provide the first synthesis of 47 studies testing the Red Queen hypothesis across a broad range of host–parasite systems to explore scale-dependent variation in parasite loads among sexual and asexual hosts.
Results/Conclusions
Our meta-analysis supports the prediction that asexual hosts experience greater parasitism loads than sexual hosts, but also points to substantial heterogeneity across scales of comparison, in particular with asexual–sexual comparisons among closely related host species within the same genus, and among hybrid species, which are common study systems for testing the Red Queen Hypothesis. These findings emphasize the need to also consider taxonomic differences among hosts used in asexual/sexual contrasts, and how these differences can impact how parasites act as selective agents for moderating the advantages/disadvantages of sexual reproduction.