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

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ABSTRACT

Analyses of intersexual conflicts-of-interest over courtship, mating or mate-guarding require an understanding of the physiological costs of sexual interaction. Repeated respirometric measures of energetic expenditure were taken on female Aquarius remigis while unladen, and while carrying a mating male, a small metal weight or a euthanized male. Unladen "cruising" locomotion consumed an average of 334.6 microwatts (uW) of energy (82 J kg^-1 m^-1); this estimate of the cost of pedestrian locomotion is moderately low compared to other insects 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 engaged in "escape" locomotion consumed 43% more energy while carrying a male than while unladen. Further, our study shows that pre-mating struggles, and therefore selective mating decisions, are energetically costly. Struggling females consumed an average of 936.6 uW, a 126% increase compared to cruising, non-struggling females, and 64% more than mating females engaged in escape locomotion. We develop a quantitative model showing that at a certain harassment rate threshold, accepting superfluous matings becomes the "best of a bad job" for females.