Social Polyandry, Parental Investment, Sexual Selection, and Evolution of Reduced Female Gamete Size

Abstract

Sexual selection in the form of sperm competition is a major explanation for small size of male gametes. Can sexual selection in polyandrous species with reversed sex roles also lead to reduced female gamete size? Comparative studies show that egg size in birds tends to decrease as a lineage evolves social polyandry. Here, a quantitative genetic model predicts that female scrambles over mates lead to evolution of reduced female gamete size. Increased female mating success drives the evolution of smaller eggs, which take less time to produce, until balanced by lowered offspring survival. Mean egg size is usually reduced and polyandry increased by increasing sex ratio (male bias) and maximum possible number of mates. Polyandry also increases with the asynchrony (variance) in female breeding start. Opportunity for sexual selection increases with the maximum number of mates but decreases with increasing sex ratio. It is well known that parental investment can affect sexual selection. The model suggests that the influence is mutual: owing to a coevolutionary feedback loop, sexual selection in females also shapes initial parental investment by reducing egg size. Feedback between sexual selection and parental investment may be common.

Parental conflict in birds: comparative analyses of offspring development, ecology and mating opportunities

“…Sexual conflict may therefore constitute primarily a feedback relationship between parental care and mating opportunities, and patterns of both parental care and polygamy depend only weakly, if at all, on ecological factors (Arnqvist & Rowe 2005). This latter theory allows for only a weak direct effect of ecological factors on parental care, for example, if species breeding where the productive season is short or unpredictable need to provide more care than those breeding where the season is longer or less seasonal (King 1974;Andersson 2004). Recent studies have highlighted the possibility of such feedback relationships (Alonzo & Warner 2000;Székely et al 2000;Andersson 2004;Alonzo in press).…”

“…For instance, in cold environments, both parents may be needed to continuously incubate the eggs and brood the young, whereas in milder climates one parent may be sufficient to supply incubation and brooding. It has been hypothesized that the spatial or temporal availability of resources or mates may dictate to what degree individuals can engage in polygamy, and that this in turn influences parental care levels ( Verner & Willson 1966;Orians 1969;Emlen & Oring 1977;Arnold & Duvall 1994;Andersson 2004). This view predicts that there should be a close relationship between ecology, the ambient environment and mating opportunities, and in turn between mating opportunities and levels of parental care.…”

The mismeasurement of sexual selection

“…Both the Bateman gradient and selection gradients used to quantify the strength of sexual selection on traits other than mating success have been referred to as 'sexual selection gradients'. To avoid confusion between the two, the regression of reproductive success on mating success is now typically referred to as the Bateman gradient (see also Andersson &Iwasa, 1996 andJones, 2009). and male fitness is mate-limited. We first assume an unbiased OSR consisting of three males and three females in which there is a moderate degree of monopolization ( Fig.…”

“…However, there was no evidence of directional selection on male body size 36. Andersson (2004) No N ⁄ A…”

Evolutionary Pathways in Shorebird Breeding Systems: Sexual Conflict, Parental Care, and Chick Development

“…This hypothesis has led to important advances in theories of mating system evolution (Emlen and Oring 1977;Davies 1991). In contrast, the sexual conflict hypothesis (SCH) suggests that mating and parental behaviors influence one another (Alonzo and Warner 2000;Székely et al 2000a;Andersson 2004). The SCH infers that the benefits of desertion depend on the mating opportunities available to each sex.…”