Figure 2.

Routes to fitness for female and male gamete producers. (a) Routes to fitness for your sex, and (b) routes to fitness for the opposite sex. The two sexes are completely interchangeable. In (a), individuals and their gametes of the focal sex are the subject of competition, and in (b) they are the object of competition. As such, in (a) selection arises within the focal sex, and in (b) selection arises within the opposite sex, as a result of gametic traits and other phenotypes in the focal sex. Both (a) and (b) will occur concurrently. Yellow lines denote routes to fitness via narrow-sense natural selection, blue lines denote routes to fitness via sexual selection, and green lines denotes routes where both natural and sexual selection may yet occur. Solid lines denote fitness routes influenced by gamete quality or quantity in the focal sex, and dotted lines denote fitness routes influenced by other traits.