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

1. Alternative reproductive tactics (ARTs) are variable, often
discontinuous, behaviours that allow a particular sex to achieve enhanced
mating success. Predation risk has been hypothesised to drive the
evolution of ARTs, but few empirical studies have examined this. It is
unclear whether predators affect fitness of the two sexes directly, by
reducing survival, or indirectly, by altering mate-searching. 2. In
crickets, mate-search typically involves acoustic signalling by males and
acoustic-mediated movement towards males by silent females. Males and
females may however employ ARTs, which includes silent searching by males,
and mating without performing phonotaxis in females. 3. 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 different levels of
predation risk. 4. 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,
with negative effects on mating success. By comparing with simulated
random movement, we found that male movement was significantly directed
towards other calling males, implying a switch to satellite strategies.
Female movement behaviour, however, remained unaltered. 5. Males and
females thus differed in their response to comparable levels of predation
risk, implying that the role of predation as a driver of alternative mate
search strategies is sex-specific.