Sex differences in alternative reproductive tactics in response to predation risk in tree crickets

Abstract

Predation risk has been hypothesised to drive the evolution of alternative mate-search strategies, but few empirical studies have examined this. In crickets, mate-search involves acoustic signalling by males and acoustic-mediated movement by females. It is unclear whether predators affect fitness of both sexes directly, by reducing survival, or indirectly, by affecting mate-searching. We empirically examined effects of increased predation risk on mate-searching behaviour and survival of male and female tree crickets, and their effects on mating success, using field-enclosure experiments with tree crickets Oecanthus henryi and their primary predator, green lynx spiders, Peucetia viridans. Crickets were allocated into three treatments with differential levels of predation risk. Increased predation risk strongly reduced survival, and thereby mating success, for both sexes. With increasing predation risk, males reduced calling and increased movement towards neighbouring callers, which had negative effects on mating success. Using simulations, we found male movement was significantly directed towards other calling males implying a switch to satellite strategies. Female movement behaviour, however, remained unaltered. Males and females thus differed in their response to comparable levels of predation risk, showing that the role of predation as a driver of alternative mate search strategies is sex and strategy-specific.