8 - The evolution of water strider mating systems: causes and consequences of sexual conflicts

Summary

ABSTRACT

Water striders (Heteroptera: Gerridae) exhibit two different types of mating behavior. The most common mating system (type I) is characterized by strong apparent conflicts of interest between the sexes, and conspicuous pre– and postcopulatory struggles. Some species exhibit a mating system that involves much less apparent conflict (type II) and lack the intense copulatory struggles.

I argue that the predominant mating system in water striders is a direct consequence of sexual conflicts over mating decisions. Matings involve high costs to females (increased predation risk and energetic expenditure) but few, if any, balancing direct benefits. Sperm–displacement rates are high, and males thus gain from rematings. Mating frequencies are high; females mate multiply for reasons of convenience. In these species, males are considered to have ‘won’ the evolutionary conflict over the mating decision in the sense that they have made acceptance of superfluous matings ‘the best of a bad job’ for females, by evolving behavioral and morphological traits that make it costly for females to reject males attempting copulations. Females, however, have apparently evolved a variety of counteradaptations to male harassment, to gain control over mating. Further, I suggest that sexual conflict may have played a crucial role in the evolution of type II matings from type I matings.