Male mate choice influences female promiscuity in Soay sheep

Abstract

In most animal species, males are predicted to compete for reproductive opportunities, while females are expected to choose between potential mates. However, when males' rate of reproduction is constrained, or females vary widely in 'quality', male mate choice is also predicted to occur. Such conditions exist in the promiscuous mating system of feral Soay sheep on St Kilda, Scotland, where a highly synchronized mating season, intense sperm competition and limitations on sperm production constrain males' potential reproductive rate, and females vary substantially in their ability to produce successful offspring. We show that, consistent with predictions, competitive rams focus their mating activity and siring success towards heavier females with higher inclusive fitness. To our knowledge, this is the first time that male mate choice has been identified and shown to lead to assortative patterns of parentage in a natural mammalian system, and occurs despite fierce male-male competition for mates. An additional consequence of assortative mating in this population is that lighter females experience a series of unstable consorts with less adept rams, and hence are mated by a greater number of males during their oestrus. We have thus also identified a novel male-driven mechanism that generates variation in female promiscuity, which suggests that the high levels of female promiscuity in this system are not part of an adaptive female tactic to intensify post-copulatory competition between males.

Male phenotypic quality influences offspring sex ratio in a polygynous ungulate

“…Indeed, the detailed data on red deer from the Isle of Rum, Scotland, have convincingly demonstrated that maternal dominance (within cohorts) affect offspring sex ratio and the subsequent fitness of those offspring as predicted by the TWM (Clutton-Brock et al 1984, 1986Kruuk et al 1999a). In some cases, male mate choice is targeted towards the most fertile females (Berger 1989;Preston et al 2005), which may confound observational studies of sex ratio trying to separate DAH and TWM, such as on Rum. However, there is currently no evidence that male mate choice is that important in red deer or reindeer.…”

Sexual Selection When Fertilization Is Not Guaranteed

“…There are examples in which much larger fractions than 1% of females do remain unmated. Insects often feature high mating investment of males in the form of time or energy (Bonduriansky 2001), and there is evidence from other taxa as well that females can become sperm limited (Wedell et al 2002;Preston et al 2005). Several studies document that sperm availability can then limit female reproductive success.…”

“…Consequently, any risk of failure should select for female mating adaptations that ensure that sperm is available for fertilization whenever needed. Finding potential examples of such adaptations is easy: prolonged sperm storage capabilities (Parker 1970;Ridley 1988), female pheromones that help males find a female (Greenfield 1981), and multiple mating (Sheldon 1994;Preston et al 2005). However, examining whether a lack of mates was responsible for the observed adaptation is challenging.…”

Unexpected male choosiness for mates in a spider

“…Nevertheless, mate guarding is both time consuming (Komdeur 2001; Bel-Venner & Venner 2006; Segoli et al 2006) and energetically costly due to fierce fights between rival males (Plaistow et al 2003;Low 2006). Males should thus benefit from selecting their mates depending on their own competitive ability and the variation in mate quality (Burley 1977;Parker 1983;Huber 2005;Preston et al 2005), both of which are reflected by body size in the populations studied here. Large females laid both more and heavier eggs than did small ones in the field (see §2).…”

“…The degree of choosiness for mates, and of withinsex competition, can be tightly linked with changes in OSR ( Forsgren et al 2004). However, in conventional sex-role species, evidence of male choosiness is accumulating (Parker 1983;Schwagmeyer & Parker 1990;Olsson 1993;Cunningham & Birkhead 1998;Amundsen 2000;Bonduriansky 2001;Dunn et al 2001;Preston et al 2005). Both theoretical and empirical evidence suggested that males should be most choosy when mating is costly and when the quality of individual females varies greatly ( Parker 1983;Johnstone et al 1996;Kvarnemo & Simmons 1998;Wong & Jennions 2003).…”