Figure 3.

Genital coevolution via sexual conflict. (A) Waterfowl, in which the elaboration of the vagina correlates with penis length (vagina on the left, penis on the right in mallard, harlequin, and long-tailed duck) Scale bars, 2 cm, and (B) seed beetles (Callosobruchus), in which the presence and abundance of spines on the aedagus correlates with the thickness of the wall of the female’s bursa copulatrix. (From Rönn et al. 2007; reprinted, with permission, from the National Academy of Sciences © 2007.)