SEXUAL CONFLICT AND THE ENERGETIC COSTS OF MATING AND MATE CHOICE IN WATER STRIDERS

Analyses of intersexual conflicts of interest over courtship, mating, or mate guarding require an understanding of the physiological costs o f sexual interaction. Repeated respirometric measures of energetic exp enditure were taken on female Aquarius remigis while unladen and while carrying a mating male, a small metal weight, or a euthanized male. U nladen ''cruising'' locomotion consumed an average of 334.6 mu W of en ergy (82 J kg(-1) m(-1)); this estimate of the cost of locomotion coin cides with measures from voluntarily locomoting arthropods of similar mass and represents the first energetic measure of skating on a water surface. Cruising females carrying males or metal weights consumed 24% and 28% more energy than unladen females, respectively. Females engag ed in ''escape'' locomotion consumed 43% more energy while carrying a male than while unladen. Further, our study shows that premating strug gles, and therefore selective mating decisions, are energetically cost ly. Struggling females consumed an average of 936.6 mu W, a 126% incre ase compared to cruising, non-struggling females, and 64% more than ma ting females engaged in escape locomotion. We develop a quantitative m odel showing that at a certain harassment rate threshold, accepting su perfluous matings becomes the ''best of a bad job'' for females.