The evolution of female ornaments and weaponry: social selection, sexual selection and ecological competition

Abstract

Ornaments, weapons and aggressive behaviours may evolve in female animals by mate choice and intrasexual competition for mating opportunities—the standard forms of sexual selection in males. However, a growing body of evidence suggests that selection tends to operate in different ways in males and females, with female traits more often mediating competition for ecological resources, rather than mate acquisition. Two main solutions have been proposed to accommodate this disparity. One is to expand the concept of sexual selection to include all mechanisms related to fecundity; another is to adopt an alternative conceptual framework—the theory of social selection—in which sexual selection is one component of a more general form of selection resulting from all social interactions. In this study, we summarize the history of the debate about female ornaments and weapons, and discuss potential resolutions. We review the components of fitness driving ornamentation in a wide range of systems, and show that selection often falls outside the limits of traditional sexual selection theory, particularly in females. We conclude that the evolution of these traits in both sexes is best understood within the unifying framework of social selection.

Color in competition contexts in non-human animals

“…The evolution of female ornaments is less well understood than that of males, and has, arguably, been limited by the typical view of Darwinian sexual selection, in which males compete for mates while females choose. Competition among females does not map onto the classical sexual selection framework easily, as in many cases females are more limited by access to resources than they are by access to mates (Tobias et al, 2012). For example, female primates gestate and suckle offspring, usually born one at a time, and provide the vast majority of offspring care.…”

“…Inter-sexual selection occurs for traits that make an individual more attractive to members of the opposite sex (e.g., female mate choice). These two concepts remain key pillars of sexual selection theory today (Andersson, 1994), although there is on-going debate as to how to accommodate female-female competition over resources within classical sexual selection theory (CluttonBrock, 2009;Tobias, Montgomerie, & Lyon, 2012).…”

Assortative mating by colored ornaments in blue tits: space and time matter

“…Indeed, quantifying mating patterns is the first step in disentangling the still‐debated factors underlying the evolution of female ornaments. For instance, female ornaments may be an evolutionary by‐product resulting from selection for male ornaments and/or emerge from direct sexual or social selection on female traits (Clutton‐Brock, 2007; Tobias, Montgomerie, & Lyon, 2012). …”

Why aren't signals of female quality more common?

“…Exaggerated ornamental traits are far more 24 common in males than females. Moreover, in at least some if not most of the species where 25 we see some female ornamentation, it is rudimentary and possibly due to inter--sexual genetic 26 correlations (Poisant et al 2010; Tobias et al 2012). Exaggerated traits are largely believed 27 to be favored in males because females tend to be choosy (as a result of their greater parental 28 investment: Trivers 1972) and males signal to attract choosy females (Andersson 1994 Taking typical sex--roles as a given, there are two classical explanations for this lack of female 42 ornamentation.…”