THE COSTS OF MATING AND MATE CHOICE IN WATER STRIDERS

Predation risk associated with the various components of the mating behaviour of the water strider Gerris buenoi are investigated with a series of experiments. Mating behaviour in this species includes frequent harassment of females by males (mate searching), pre-mating struggles that may function as mate choice by females, mating which includes copulation and male mate guarding, and post-mating struggles. Each component of the mating behaviour of females increases predation risk. Escape by females from harassment by males increases the movement rate of females and predacious backswimmers are attracted to movement at the water surface. Capture success of backswimmers is almost tripled on females engaged in pre- and post-mating struggles relative to single females. Because longer pre-mating struggles are one mechanism by which females bias the mating success of male phenotypes in water striders, these data demonstrate that mate choice is costly to females. Finally, mating females are at twice the risk of predation than are single females. Some components of mating behaviour in males also appear to increase predation risk. Males searching for mates spend a higher portion of their time in the open water habitat (out of refuge) and move more often than females. Use of the open water habitat increases exposure to backswimmers and movement on the surface attracts backswimmers. Males that successfully grasp females engage in pre-mating struggles, during which capture success by backswimmers on males is significantly increased. However, in contrast to females, there was no significant increase in capture success of backswimmers on mating relative to single males.