A conceptual review of mate choice: stochastic demography, within-sex phenotypic plasticity, and individual flexibility

Abstract

Mate choice hypotheses usually focus on trait variation of chosen individuals. Recently, mate choice studies have increasingly attended to the environmental circumstances affecting variation in choosers' behavior and choosers' traits. We reviewed the literature on phenotypic plasticity in mate choice with the goal of exploring whether phenotypic plasticity can be interpreted as individual flexibility in the context of the switch point theorem, SPT (Gowaty and Hubbell 2009). We found >3000 studies; 198 were empirical studies of within-sex phenotypic plasticity, and sixteen showed no evidence of mate choice plasticity. Most studies reported changes from choosy to indiscriminate behavior of subjects. Investigators attributed changes to one or more causes including operational sex ratio, adult sex ratio, potential reproductive rate, predation risk, disease risk, chooser's mating experience, chooser's age, chooser's condition, or chooser's resources. The studies together indicate that "choosiness" of potential mates is environmentally and socially labile, that is, induced - not fixed - in "the choosy sex" with results consistent with choosers' intrinsic characteristics or their ecological circumstances mattering more to mate choice than the traits of potential mates. We show that plasticity-associated variables factor into the simpler SPT variables. We propose that it is time to complete the move from questions about within-sex plasticity in the choosy sex to between- and within-individual flexibility in reproductive decision-making of both sexes simultaneously. Currently, unanswered empirical questions are about the force of alternative constraints and opportunities as inducers of individual flexibility in reproductive decision-making, and the ecological, social, and developmental sources of similarities and differences between individuals. To make progress, we need studies (1) of simultaneous and symmetric attention to individual mate preferences and subsequent behavior in both sexes, (2) controlled for within-individual variation in choice behavior as demography changes, and which (3) report effects on fitness from movement of individual's switch points.

Keywords: Adaptive flexibility; OSR; choosy; genetic complementarity; indiscriminate; mate choice; parasite load; switch point theorem.

Figure 1

The evolution of adaptive, fitness enhancing, and flexible individuals (the fourth column above) able to switch their reproductive decisions based on their current demographic situations depends upon probabilistic (stochastic) variation in (first column above) a focal individual's encounter probability with potential mates, e, their survival probability s, the duration of any postmating time‐outs that the focal has experienced o, and the number of potential mates in the population n, which together predict an individual's expected mean lifetime number of mates under demographic stochasticity. The second column above indicates the SPT's explicit dependence upon the within‐population random distribution of fitness that would be conferred. The third column above indicates that the SPT assumes that selection occurred so that what evolved was (1) individual sensitivities to probabilities of encounter of potential mates e, probability of survival s, the duration of postmating time‐outs o, and the number of potential mates in the population n and the w‐distribution and in (2) abilities to assess the fitness that would be conferred by any potential mate. The SPT proved mathematically (the fourth column above) that individuals fixed in their reproductive behavior would be selected against relative to flexible individuals able to make real‐time mating decisions fit to their current ecological and social situations, as though decision‐makers are Bayesians able to update their priors to better fit their actions to the demographic and social circumstances they are in (Gowaty and Hubbell 2013).