Figure 1.

Sexual conflict over mating rate. (a) In this example, we consider a system in which more mating increases male fitness but decreases female fitness (+ and – signs along pathways I for males and females, respectively). Sexual conflict is generated by these opposing effects of mating rate on male and female fitness (w), and results in selection favouring male and female traits that shift mating rate towards each sex's optimum (+ and – signs along pathways II). Sex-specific traits have positive indirect effects on each sex's fitness through effects on mating rate (dashed lines), along with negative direct effects borne by each sex (e.g. trait costs; solid lines). Ecological variation can be expected to shape relationships between traits, mating rate and fitness, at pathways I, II and III (see §2). Adapted with permission from Rowe and Day [29]. (b) Each sex's optimum is set by the balance of sex-specific benefits and costs; arrows indicate the direction of selection. Benefits and costs will be influenced by the local environment; for example, the sexes might experience conflict over a wider range of mating rates in one environment than another. Adapted with permission from Rowe et al. [30].