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Sexual signal evolution is shaped by whether only one or both sexes execute mate choice. When mate choice by both sexes is considered, the same signalling modality is generally inferred for males and females. In the noctuid moth Chloridea (Heliothis) virescens (Lepidoptera: Noctuidae), both sexes may be signallers and responders, as both emit a sex-specific pheromone. Male mate choice is based on the female sex pheromone, perceived via the antennae, and has been well documented. However, whether females choose partners and whether their choice is based on the male pheromone are unknown. Since female mate choice is expected when males vary in quality, we reared males on two different larval diets that affected their size, which correlated positively with their fitness. When given a choice, more females mated with larger than with smaller males, and these females produced more eggs and larvae. Female choice was not affected by the absolute amount or composition of the male pheromone. Moreover, we found that antennaless females mated as readily as intact females, indicating that antennal sensory input is not required for females to mate. To determine whether females make an active choice, we studied courtship behaviour in detail and observed that females determined the outcome of courtship by moving away from the male (avoidance) or by facilitating copulation with an abdominal bend (acceptance). Additionally, we discovered that tactile sensory stimuli may be involved during courtship. Because tactile interactions may mediate contact-based (chemical) communication, we also investigated putative pheromone components on moth legs, but found no differences between the sexes. Together, our study is the first comprehensive investigation of female mate choice in a heliothine moth.

Factors affecting the evolution of plumage conspicuousness in females are nowadays the focus of debate, and here we explore the possibility that the conspicuousness of female plumage and male participation in nest building are associated in birds. We hypothesize that males that participate in nest building will gain higher fecundity from high-quality ornamented females, whereas ornamented females will adjust fecundity to the costly nest-building behaviour of males. Large-sized species might experience higher costs of nest building and, thus, body size should affect the scenario described above. We used information on male contribution to nest construction (yes/no), male and female conspicuousness (conspicuous or cryptic plumage) and body size of Western Palaearctic passerines. In accordance with the hypothesis, we found that female conspicuousness, in interaction with body mass, was strongly associated with male participation in nest building. For large-sized species, female conspicuousness was positively associated with male participation in nest building. Discrete analyses of correlated evolution rendered evidence of female conspicuousness determining the evolution of male contributions to nest building, with the loss of female conspicuousness occurring more frequently before the loss of male participation in nest building. We discuss possible adaptive scenarios explaining the detected evidence because of mutual sexual selection in males and females, The study was financed by the Ministerio de Economía y Competitividad MINECO (CGL2013-48193-C3-1-P, CGL2013-48193-C3-2-P, CGL2013-48193-C3-3-P and CGL2017-83103-P) and the European Regional Development Fund (FEDER)

Many conspicuous ornamental traits in animals are expressed in both males and females. Despite this, most research has focused on sexually dimorphic ornamentation. Mutual ornamentation has often been viewed as a result of either a nonadaptive genetic correlation between the sexes or similar selection pressures in both sexes. Here, we review the theoretical underpinning and empirical evidence for these ideas. Few studies have attempted to test empirically whether a genetic correlation between the sexes can constrain the evolution of sexual dimorphism, and the results have been mixed. By contrast, there is good evidence that mutual ornaments can have a signal function in both sexes, especially in terms of mate choice. Other possible signalling functions have received little attention. Social status signalling is especially likely to be important, because competition over nonsexual resources is more balanced between the sexes than sexual competition. There is a need for experimental studies that explicitly test these hypotheses simultaneously in both sexes.

Many conspicuous ornamental traits in animals are expressed in both males and females. Despite this, most research has focused on sexually dimorphic ornamentation. Mutual ornamentation has often been viewed as a result of either a nonadaptive genetic correlation between the sexes or similar selection pressures in both sexes. Here, we review the theoretical underpinning and empirical evidence for these ideas. Few studies have attempted to test empirically whether a genetic correlation between the sexes can constrain the evolution of sexual dimorphism, and the results have been mixed. By contrast, there is good evidence that mutual ornaments can have a signal function in both sexes, especially in terms of mate choice. Other possible signalling functions have received little attention. Social status signalling is especially likely to be important, because competition over nonsexual resources is more balanced between the sexes than sexual competition. There is a need for experimental studies that explicitly test these hypotheses simultaneously in both sexes.

We investigated the adaptive significance of a sexually monomorphic ornament in the black swan Cygnus atratus. Both sexes grow curled feathers on their wings (range 7‐22 curled feathers per wing), which are displayed prominently in a range of social interactions. The number of curled feathers increased until the birds reached sexual maturity (at 2 years of age) but did not vary with age thereafter. We found evidence for both sexual and social functions of the ornament. Paired, mature individuals of both sexes had higher numbers of curled feathers than unpaired, mature birds, and individuals paired assortatively with respect to curled feather number, suggesting the feathers may be involved in mutual sexual selection. More ornamented individuals were dominant in agonistic interactions with birds of the same sex and pairing status. Highly ornamented pairs were also more likely to maintain extended tenancy of preferred cygnet feeding areas, which resulted in improved offspring survival. The curled feathers thus appear to function as a signal of social dominance, which is highly correlated with reproductive success and is therefore a reliable signal of parental quality in mate choice. Key words: black swans, Cygnus atratus, dominance, mutual sexual selection, ornamentation, signaling, social selection. [Behav Ecol 15:380–389 (2004)]