The dark side of sexual selection

[Extract] A casual reader of the behavioural ecology literature might think that sexual selection provides boundless evolutionary benefits to females. Females can directly choose a mate, or let males establish their worth by fighting amongst themselves for the chance to mate. We know that males trade the advantages of being chosen as a mate against the energy loss and risk to their lives of competing with one another and signalling to females. In contrast, our understanding of the process from the female perspective is dominated by attempts to resolve the benefits that females derive from mate choice or from multiple mating. The idea that a single mating can decrease a female's lifespan, and each additional mating or refusal to mate further decreases her survival and fecundity has received attention from only a handful of researchers.\ud \ud The hidden costs to females when males compete to mate can be understood in terms of conflict between the sexes in the way that reproductive success is optimized5. A competitive male that outsignals or outfights other males will mate with more females and thus sire more offspring, even if his actions lead to a reduction in each mated female's reproductive output. The higher the potential variance in male mating success, the more important sexual selection becomes, and the greater the likelihood that it will lead to the evolution of traits incidentally harmful to females6. Female mate choice is one, but by no means the only, female adaptation that results from competition between males for mates. How females balance the costs of courtship and harassment by males with those of mating (e.g. sperm toxicity7 and vulnerability to predators2) is a crucial aspect of female ecology. Variation in female tendency to remate greatly influences the strength and form of sexual selection in a population