Sex-specific manipulation of sexually cannibalistic mantid mating behavior by hairworms

Changes in the morphology, physiology, and behavior of parasitized organisms provide an ideal opportunity to examine the extended phenotype of parasites. Because the quality of the host directly affects the fitness of the parasite, parasites may increase their fitness by manipulating phenotypes of low-quality hosts. Males are usually preyed on by females in sexual cannibalism. Thus, the males of sexually cannibalistic species are unsafe and low-quality hosts for parasites, whereas females may be beneficial hosts because of the chance of nutrient intake from cannibalized males. Under passive modes of transmission, parasites cannot choose the host sex. Such parasites exploiting sexually cannibalistic organisms are subjected to contrasting fitness effects and may evolve to manipulate host mating behavior in a sex-specific manner: decreasing male mating to avoid cannibalism and promoting female mating to engage in cannibalism. We examined this hypothesis by a behavioral experiment using a mantid–hairworm system. Parasitized male mantids (Tenodera angustipennis) changed their behavior as expected, exhibiting increased escapes and decreased courtships and mountings, potentially avoiding encounters with the female. Interestingly, male attack behavior was promoted, possibly decreasing contact with the encountered female. However, contrary to our prediction, parasitized females also exhibited decreased propensities of mating, suggesting costs or little benefits of host mating for parasites in the female host. This study provides novel insights into the evolution of parasite strategies in response to sexual differences in host quality.