Mate‐sampling costs and sexy sons

Abstract

Costly female mating preferences for purely Fisherian male traits (i.e. sexual ornaments that are genetically uncorrelated with inherent viability) are not expected to persist at equilibrium. The indirect benefit of producing 'sexy sons' (Fisher process) disappears: in some models, the male trait becomes fixed; in others, a range of male trait values persist, but a larger trait confers no net fitness advantage because it lowers survival. Insufficient indirect selection to counter the direct cost of producing fewer offspring means that preferences are lost. The only well-cited exception assumes biased mutation on male traits. The above findings generally assume constant direct selection against female preferences (i.e. fixed costs). We show that if mate-sampling costs are instead derived based on an explicit account of how females acquire mates, an initially costly mating preference can coevolve with a male trait so that both persist in the presence or absence of biased mutation. Our models predict that empirically detecting selection at equilibrium will be difficult, even if selection was responsible for the location of the current equilibrium. In general, it appears useful to integrate mate sampling theory with models of genetic consequences of mating preferences: being explicit about the process by which individuals select mates can alter equilibria.

Fisher's lost model of runaway sexual selection

“…Maybe Fisher never derived a mathematical model that met his high standards. Notably, many later models of the runaway process (Lande 1981;Pomiankowski et al 1991;Iwasa and Pomiankowski 1995;Day 2000;Kokko et al 2015) and of sexual selection more generally (Grafen 1990;Iwasa et al 1991;Tazzyman et al 2014;Dhole et al 2018: reviewed in Kuijper et al 2012 are characterized by considerable analytical sophistication and by numerical techniques that were unavailable or impractical in Fisher's pre-digital era.…”

The relation between R. A. Fisher's sexy-son hypothesis and W. D. Hamilton's greenbeard effect

“…Notable exceptions are the models of Pomiankowski () and Kokko et al. (), in which the cost of female preference is explicitly assumed to decrease as the frequency of ornamented males increases, implying facultative female preference. More generally, a mixture of facultative and obligate effects will often be more realistic, as some of the costs of female preference (e.g., the hazards of rejecting unwanted mating attempts) are likely to vary as a function of the rate of encounters with ornamented versus unornamented males, whereas others (e.g., overhead investment into requisite cognitive machinery) are likely to remain relatively constant.…”

“…The models of Pomiankowski () and Kokko et al. () are, again, exceptional in this respect: they explicitly assume that female preference is exerted by rejection of unornamented males, and hence describe greenbeards of the harming variety. To our knowledge, no model of the sexy‐son hypothesis has yet been developed that takes an explicitly helping approach, such that preference is exerted by choosy females being just as receptive to unornamented males as are nonchoosy females, but being more receptive to ornamented males than are nonchoosy females.…”

Direct detection of male quality can facilitate the evolution of female choosiness and indicators of good genes: Evolution across a continuum of indicator mechanisms

“…When search costs are frequency-independent, the latter effect does not take place, although the former does. Although frequency-independent search costs are stronger, for a given s h , than frequency-dependent costs (see Kokko et al 2015), overall evolution of both choosiness and the display behave very similarly across the continuum of indicators mechanisms with frequency-independent search costs vs. with frequency-dependent ones (compare Fig. S3, S4 to Fig.…”