Postmating sexual selection: the effects of male body size and recovery period on paternity and egg production rate in a water strider

The role of male body size in postmating sexual selection was explored in a semiaquatic insect, the water strider Gerris lateralis. To separate effect s of male size per se from those due to numeric sperm competition, male rec overy period (shown here to be proportional to ejaculate size) was manipula ted independently of body size in a factorial experiment where virgin femal es were mated first with sterile males and then with focal males. Both rela tive male fertilization success and female reproductive rate were measured. The number of sperm transferred increased with male recovery period, an ef fect that was mediated by longer copulation duration, but there were no eff ects of body size on ejaculate size. Neither male size nor recovery period had any significant direct effects on male fertilization success. However, copulation duration influenced relative fertilization success, suggesting t hat males able to transfer more sperm also achieved higher fertilization su ccess. Females exercised cryptic female choice by modulating their reproduc tive rate in a manner favoring large males and males that were successful i n terms of achieving high relative fertilization success. Thus, successful males gained a twofold advantage in postmating sexual selection. This study has important implications for previous estimates of sexual selection in t his group of insects because pre- and postmating sexual selection will be a ntagonistic due to limitations in male sperm production: males mating frequ ently (high mating success) will on average transfer fewer sperm in each ma ting and will hence tend to fertilize fewer eggs per mating (low fertilizat ion success).