Female response to predation risk alters conspecific male behaviour during pre-copulatory mate guarding

Mating behaviour often increases predation risk, but the vulnerability within mating pairs differs between the sexes. Such a sex difference is expected to lead to differences in responses to predation risk between the sexes. In the two-spotted spider mite Tetranychus urticae, males engage in pre-copulatory mate guarding because only the first mating results in fertilisation. We investigated (i) whether pre-copulatory pairs are more conspicuous to the predatory mite Phytoseiulus persimilis than solitary females, (ii) whether the vulnerability to the predator differs between sexes within the pre-copulatory pair, (iii) whether each sex of T.urticae responds to predation risk during pre-copulatory mate guarding and (iv) whether T.urticae's response to predation risk affects predator behaviour. Because T.urticae females are immobile during pre-copulatory mate guarding, we observed male behaviour to evaluate effects of predation risk. We found that the predators detect more pre-copulatory pairs than solitary females and that more females than males of the pre-copulatory pairs are preyed upon by the predators. The preference of spider mite males for pre-copulatory pairs versus solitary females was affected by whether or not the female had been exposed to predators during development. Male T.urticae exposed to predation risk did not alter their behaviour. These results suggest that only the most vulnerable sex, that is the female, responds to predation risk, which modifies male behaviour. Regardless of T.urticae females' experience, however, P.persimilis detected more T.urticae pre-copulatory pairs than solitary females, suggesting that pre-copulatory mate guarding itself is dangerous for T.urticae females when these predators are present. We discuss our results in the context of sex-dependent differences in predation risk.