Infection of parthenogenetic lizards by blood parasites does not support the "Red Queen hypothesis" but reveals the costs of sex.

Abstract

Sexual organisms should be better suited than asexual ones in a context of continuous evolution in response to opposite organisms in changing environments ("Red Queen" hypothesis of sex). However, sex also carries costs associated with the maintenance of males and mating (sex cost hypothesis). Here, both non-mutually excluding hypotheses are tested by analysing the infestation by haemogregarines of mixed communities of Darevskia rock lizards composed of parthenogens generated by hybridisation and their bisexual relatives. Prevalence and intensity were recorded from 339 adult lizards belonging to six species from five syntopic localities and analysed using Generalized Mixed-Models (GLMM). Both infestation parameters depended on host-size (like due to longer exposure with age), sex and, for intensity, species. Once accounting for locality and species, males were more parasitized than conspecific females with bisexual species, but no signal of reproductive mode itself on parasitization was recovered. Essentially, male-male interactions increased haemogregarine intensity while females either sexual or asexual had similar reproductive costs when in the same conditions. These findings deviate from the predictions from "Red Queen" dynamics while asymmetric gender costs are here confirmed. Thus, increased parasitization pressure on males adds to other costs, such as higher social interactions and lower fecundity, to explain why parthenogenetic lizards apparently prevail in the short-term evolutionary scale. How this is translated in the long-term requires further phylogenetic analysis.