Costs of breeding and their effects on the direction of sexual selection.

A recent life-history model has challenged the importance of the operational sex ratio and the potential reproductive rates of males and females as the factors most important for the control of sexual selection, arguing that the cost of breeding, interpreted as the probability of dying as a consequence of the current breeding attempt, is the single most important factor that best predicts a mating system. In one species of bushcricket, the mating system can be reversed by resource manipulation. Here, we examine the costs of breeding in this system. Consistent with the model, increased costs of breeding can explain female competition and increased male choosiness under resource limitation. However, this is due to differences in the time required for a breeding attempt, rather than differences in breeding mortality which did not differ between the sexes. In general, males lived longer than females and we discuss the possible reasons behind this pattern of sex-biased non-breeding mortality.