Selection on female remating interval is influenced by male sperm competition strategies and ejaculate characteristics

Abstract

Female remating rate dictates the level of sperm competition in a population, and extensive research has focused on how sperm competition generates selection on male ejaculate allocation. Yet the way ejaculate allocation strategies in turn generate selection on female remating rates, which ultimately influence levels of sperm competition, has received much less consideration despite increasing evidence that both mating itself and ejaculate traits affect multiple components of female fitness. Here, we develop theory to examine how the effects of mating on female fertility, fecundity and mortality interact to generate selection on female remating rate. When males produce more fertile ejaculates, females are selected to mate less frequently, thus decreasing levels of sperm competition. This could in turn favour decreased male ejaculate allocation, which could subsequently lead to higher female remating. When remating simultaneously increases female fecundity and mortality, females are selected to mate more frequently, thus exacerbating sperm competition and favouring male traits that convey a competitive advantage even when harmful to female survival. While intuitive when considered separately, these predictions demonstrate the potential for complex coevolutionary dynamics between male ejaculate expenditure and female remating rate, and the correlated evolution of multiple male and female reproductive traits affecting mating, fertility and fecundity.

The polyandry revolution

“…female remating versus sperm utilization), and changes dynamically over evolutionary times. Alonzo & Pizzari [23] present a theoretical framework to analyse the coevolutionary dynamics arising from different effects that mating can have on female fertility, fecundity and mortality. The study shows how selection on female propensity for polyandry is determined by the complex interactions of such effects.…”

Sexual Conflict Arising from Extrapair Matings in Birds

“…However, when females mate with more than one male, sexual conflict necessarily becomes a multiplayer game. The players include at least the pair female, pair male, and extrapair male (Petrie and Kempenears 1998;Rice 1998;Westneat and Stewart 2003;Alonzo and Pizzari 2013). In some cases, the female paired with the extrapair male may also suffer fitness losses because of her mate's activities, in which case, the conflict becomes a fourplayer game (Petrie and Kempenaers 1998).…”

“…The two males will typically be in conflict over the occurrence of the EPCs because they compete to fertilize the same ova-usually a zero-sum game. Although male -male cooperation over matings with a single female is theoretically feasible (e.g., when courtship and copulation with different males greatly stimulate female fecundity [Alonzo and Pizzari 2013]), this idea remains to be tested empirically. These conflict-of-interest diagrams help to illustrate how conflict changes under different social scenarios.…”

“…Any benefits gained by the extrapair male are thought to lead to direct fitness costs for the within-pair male because the within-pair male then sires fewer offspring than he would otherwise. But EPP may cause females to increase their investment, either through the stimulatory effects of ejaculates from multiple males (Alonzo and Pizzari 2013) or when females engage in EPP to upgrade the genetic quality of their offspring, resulting in differential allocation of maternal care (Burley 1988). Thus, changes in female investment should be considered when evaluating the fitness costs to the pair male and the effects on his contribution to parental care (Sheldon 2000(Sheldon , 2002.…”

“…Traits shows plasticity when their expression depends on the mating role in which they are manifest (e.g., different expression in extrapair versus within-pair males) (Fig. 1) (Petrie and Kempenaers 1998;Ball and Parker 2003;Westneat and Stewart 2003;Parker 2006;Alonzo and Pizzari 2013). Role-specific traits must necessarily be flexible, and they also require an assessment…”