Sexual Selection When Fertilization Is Not Guaranteed

Abstract

Abstract. Much of the theory of sexual selection assumes that females do not generally experience difficulties getting their eggs fertilized, yet sperm limitation is occasionally documented. How often does male limitation form a selection for female traits that improve their mating rate? The question is difficult to test, because if such traits evolve to be efficient, sperm limitation will no longer appear to be a problem to females. Here, we suggest that changes in choosiness between populations, and in particular between virgin and mated females, offer an efficient way to test this hypothesis. We model the ''wallflower effect,'' that is, changes in female preferences due to time and mortality costs of remaining unmated (for at least some time). We show that these costs cause adaptive reductions of female choice, even if mate encounter rates appear high and females only rarely end their lives unfertilized. We also consider the population consequences of plastic or fixed mate preferences at different mate encounter rates. If mate choice is plastic, we confirm earlier verbal models that virgins should mate relatively indiscriminately, but plastic increase of choosiness in later matings can compensate and intensify sexual selection on the male trait, particularly if there is last male sperm precedence. Plastic populations will cope well with unusual conditions: eagerness of virgins leads to high reproductive output and a relaxation of sexual selection at low population densities. If females lack such plasticity, however, population-wide reproductive output may be severely reduced, whereas sexual selection on male traits remains strong.

Socially flexible female choice differs among populations of the Pacific field cricket: geographical variation in the interaction coefficient psi (Ψ)

“…Empirically, it is well established that females change their mate preferences based on prior experience [37 -41], that they can become choosier when a range of male phenotypes is experienced [21,42], and that both sexes can learn about the distribution of male phenotypes in the environment based on interactions with conspecifics [26,43,44]. Taken together, these observations validate theoretical models that predict that females should flexibly modify their choosiness based on social interactions, that different populations should vary in that flexibility and that populations experiencing sexual selection should exhibit strong, positive C [9,45]. Quantifying C for traits involved in mate choice should yield insights about the dynamics of sexual selection in a given population or species [46].…”

Lonely hearts or sex in the city? Density-dependent effects in mating systems

“…Thus, while one can imagine dispersal rules that lead to high-density aggregations in both sexes, the example of figure 1b shows that the details of adaptive mate searching rules can retain, or even accentuate, the effects of low density. The need of females to adapt to situations of high or low mate availability should, therefore, not be immediately dismissed (Kokko & Mappes 2005).…”

“…Unsurprisingly, models that incorporate mate encounter rates generally predict that females become less selective when mate availability is low (Hubbell & Johnson 1987;Crowley et al 1991;Kokko & Monaghan 2001;Härdling & Kaitala 2005;Kokko & Mappes 2005), yet few studies have predicted the net effect on the rate of multiple mating (but see Härdling & Kaitala 2005). A less direct way to assess the effects of density is achieved by varying the cost of mate sampling: low density corresponds to high costs of locating another male.…”

“…What is clear is that there are good reasons to believe that female behaviours can lead to very different sexual selection at varying densities, and this does not necessarily require particularly sophisticated reaction norms. For example, females often mate relatively indiscriminately when they first mate ( Jennions & Petrie 2000;Kokko & Mappes 2005). This makes sense: compared to the often slight effects of male quality, it makes a large difference to female fitness whether she can commence reproduction at all.…”

The Mothematics of Female Pheromone Signaling: Strategies for Aging Virgins

“…However, equation (2) is not valid for situations where females cannot be certain about local male density. While females possess evolutionary knowledge regarding typical male densities, circumstances will often deviate from the average (Kokko and Mappes 2005), and females should adjust their signaling effort over time if previous efforts have not led to a desirable male arrival rate. Consider the female in a habitat patch where signaling leads to a low arrival rate, described by l L (S) p 5 (1 Ϫ exp(ϪS)), or in a patch where higher arrival rates can be expected, l H (S) p 10 (1 Ϫ exp(ϪS)) (depicted in fig.…”