Female ornaments revisited – are they correlated with offspring quality?

Abstract

Summary1. The evolution and signalling content of female ornamentation has remained an enduring challenge to evolutionary biologists, despite the fact that secondary sexual characters are widespread in females. While females usually invest significant amounts of their resources, including carotenoids, in offspring, all the resources allocated to elaborate ornamentation reduce resources available for other purposes. This may in turn constrain female fitness leading to dishonest female signalling. 2. We review the literature for empirical studies on mutually ornamented species with conventional sex roles, by focusing on the association between female ornaments and quality of their offspring. 3. We found 43 papers where 33 (77%) are bird-studies, nine (21%) are on fishes, and one (2%) is a lizard-study. Nine of these report negative, 14 non-existing, and 20 positive associations between female ornament and offspring quality. Eighteen of the bird studies (55%) show a positive association between the two traits investigated, whereas five (15%) of the studies report a negative association. The number of fish studies, although few, is skewed in the opposite direction with two (22%) and four (44%) studies supporting positive and negative association, respectively. A minority of studies on carotenoids-based ornaments reports a positive association (4 of 18 studies, or 22%) between the traits, which is low compared to studies on non-carotenoids-based ornaments (16 of 25 studies, or 64%). 4. The above-mentioned relative large number of studies with negative association, especially common in studies on fishes and in carotenoids-based-ornaments, challenges the generality of the direct selection hypothesis to account for female fineries. This is important because this hypothesis seems to have strong support in recent literature on the topic. In the present paper, we also propose possible explanations for the observed differences between taxa and suggest directions and ideas for future research on the evolution of female ornamentation.

Determinants of making success in female Tree Swallows (Tachycineta Bicolor)

“…Previous studies in tree swallows also have shown that more ornamented females have greater levels of nest parasitism, poorer immune defences, lower hematocrit levels and produce offspring that are smaller or in poor condition (Coady, 2011;Bentz and Siefferman, 2013). This negative relationship between female ornamentation and offspring quality could be interpreted as evidence in support of the genetic correlation hypothesis (Nordeide et al, 2013); however, more ornamented female tree swallows may experience social costs as a result of conspecifics challenging their status (Coady, 2011;Chapter 3), thereby resulting in poorer quality offspring produced by more ornamented females.…”

“…In contrast, traits that appear to not be preferred by males or reflect female quality, or are negatively related to offspring quality (e.g., Muma and Weatherhead, 1989;Cuervo et al, 1996;Wolf et al, 2004; reviewed in Nordeide et al, 2013), are hypothesized to evolve as a by-product of selection acting on ornamentation displayed by males (i.e., genetic correlation hypothesis, Lande, 1980). The focus of studies on male mate choice, however, may be too narrow to fully understand the evolution of ornamentation in females (Tarvin and Murphy, 2012), especially since ornamental traits, such as aggressive behaviour, may enable females to outcompete conspecifics (Rosvall, 2008), but entail costs to offspring quality (Rosvall, 2011b).…”

“…Female animals from a wide variety of taxa display 'male-like' traits, such as elaborate or brightly coloured plumage, and despite increased recent empirical investigation, explaining the function and evolution of such traits has remained a challenge (e.g., Tarvin and Murphy, 2012;Tobias et al, 2012;Nordeide et al, 2013). In species where both sexes display elaborate ornamentation, such traits may evolve by mutual sexual selection (Kraaijeveld et al, 2007) if they provide an advantage to females in competition for access to mates (Johnson, 1988), or are attractive to or preferred by males (e.g., Torres and Velando, 2005;Griggio et al, 2009).…”

“…For example, females that invest resources, such as carotenoids, into the production of elaborate ornaments have been observed to produce poor-quality eggs (Morales et al, 2009). Consequently, males of mutually ornamented species may not benefit from choosing the most elaborately ornamented females as mates if their offspring are lower quality, and thus a negative relationship between female ornamentation and offspring quality is interpreted as support for the genetic correlation hypothesis (Nordeide et al, 2013). While this explanation may be limited to species where allocation of resources to the production of ornamentation and offspring coincide during the breeding season and/or male mate choice has been shown to operate (reviewed in Nordeide et al, 2013), it is also important to consider alternative explanations that may arise by social mechanisms that maintain signal honesty.…”

“…Consequently, males of mutually ornamented species may not benefit from choosing the most elaborately ornamented females as mates if their offspring are lower quality, and thus a negative relationship between female ornamentation and offspring quality is interpreted as support for the genetic correlation hypothesis (Nordeide et al, 2013). While this explanation may be limited to species where allocation of resources to the production of ornamentation and offspring coincide during the breeding season and/or male mate choice has been shown to operate (reviewed in Nordeide et al, 2013), it is also important to consider alternative explanations that may arise by social mechanisms that maintain signal honesty. For example, enlarging the size of forehead patch of male collared flycatchers (Ficedula albicollis) increased competition among males, and yearling males displaying enlarged forehead patches spent more time involved in competition and as a result, provisioned their nestlings less compared to control males (Qvarnström, 1997).…”