Fecundity selection theory: concepts and evidence

Abstract

Fitness results from an optimal balance between survival, mating success and fecundity. The interactions between these three components of fitness vary depending on the selective context, from positive covariation between them, to antagonistic pleiotropic relationships when fitness increases in one reduce the fitness of others. Therefore, elucidating the routes through which selection shapes life history and phenotypic adaptations via these fitness components is of primary significance to understanding ecological and evolutionary dynamics. However, while the fitness components mediated by natural (survival) and sexual (mating success) selection have been debated extensively from most possible perspectives, fecundity selection remains considerably less studied. Here, we review the theoretical basis, evidence and implications of fecundity selection as a driver of sex-specific adaptive evolution. Based on accumulating literature on the life-history, phenotypic and ecological aspects of fecundity, we (i) suggest a re-arrangement of the concepts of fecundity, whereby we coin the term 'transient fecundity' to refer to brood size per reproductive episode, while 'annual' and 'lifetime fecundity' should not be used interchangeably with 'transient fecundity' as they represent different life-history parameters; (ii) provide a generalized re-definition of the concept of fecundity selection as a mechanism that encompasses any traits that influence fecundity in any direction (from high to low) and in either sex; (iii) review the (macro)ecological basis of fecundity selection (e.g. ecological pressures that influence predictable spatial variation in fecundity); (iv) suggest that most ecological theories of fecundity selection should be tested in organisms other than birds; (v) argue that the longstanding fecundity selection hypothesis of female-biased sexual size dimorphism (SSD) has gained inconsistent support, that strong fecundity selection does not necessarily drive female-biased SSD, and that this form of SSD can be driven by other selective pressures; and (vi) discuss cases in which fecundity selection operates on males. This conceptual analysis of the theory of fecundity selection promises to help illuminate one of the central components of fitness and its contribution to adaptive evolution.

Function‐related Drivers of Skull Morphometric Variation and Sexual Size Dimorphism in a Subterranean Rodent, Plateau Zokor (Eospalax baileyi)

“…Alternatively, the variation in body size might result from faster growth rates of one of the sexes, or individuals of one sex might grow for a longer time F I G U R E 5 Linear regression between log (male body size) on log (female body size) in plateau zokors (a) and that of plateau zokors with eight other zokor species (b) F I G U R E 6 Linear regression between log (litter size) on log (female body size) in females (a) and distribution of testicle size to body size in males (b) plateau zokors than the opposite sex (Blanckenhorn et al, 2007). Our results revealed that different age-groups showed alterations in different morphological traits mainly owing to the growth and maturation of animals that might also reflect the different habits between males and females for the ingestion of diverse food items for heat production in cold climates in addition to other physiological regulators of food intake (Patterson & Abizaid, 2013). The bigger morphological traits in males in group I during the initial stages of development validate the assumption that SSD starts as early as possible, which supports the body for further growth and development as age advances (Le Galliard, Massot, Landys, Meylan, & Clobert, 2006).…”

“…The sexual selection hypothesis (Blanckenhorn et al, 2007) predicts that larger males might compete more efficiently to gain access to mates for better reproductive success and this drives MBSSD (Stillwell, Blanckenhorn, Teder, Davidowitz, & Fox, 2010). The fecundity selection theory states that larger females would produce higher numbers of healthier offspring and/ or reproduce more frequently than smaller ones, thereby driving FBSSD or "reversed" sexual size dimorphism (Pincheira-Donoso & Hunt, 2017). An alternative, sex-based ecological divergence (Brown, Madsen, & Shine, 2017) hypothesis states that SSD evolves to facilitate different sexes to exploit the available resources differently to reduce competition between them (Szekely, Reynolds, & Figuerola, 2000).…”

Intrasexually selected weapons

“…For instance, spiders are one of the few groups that exhibit ISWs in which males are not larger than females. Female-biased sexual size dimorphism, prevalent in invertebrates and ectothermic vertebrates (but also occurring in endotherms; Ralls, 1976), is probably a result of fecundity selection (Darwin, 1871;Andersson, 1994;Pincheira-Donoso & Hunt, 2017). In spiders, an additional selective factor that keeps males smaller than females is related to enhanced dispersal abilities of males while searching for mates (Corcobado et al, 2010).…”

“…In this review, we follow the traditional division of sexually dimorphic traits in three groups: primary, secondary, and ecological sex traits (Darwin, 1871;Andersson, 1994;Williams & Carroll, 2009); yet we highlight the necessity of an in-depth discussion of this classification taking into account fecundity selection (review in Pincheira-Donoso & Hunt, 2017), social competition (West-Eberhard, 1983), and sexual differences in offspring care or other behaviours associated with reproduction (e.g. Cade & Maclean, 1967;Wilson et al, 2003;Ponssa & Barrionuevo, 2012).…”

Allometry for sexual dimorphism in millipedes (Diplopoda)

“…21] . Rensch's rule may be explained by sexual selection and fecundity selection [22][23][24][25][26][27][28][29] . The macro-evolutionary pattern is unresolved in Diplopoda [30] .…”