Expression Of Sexual Signals Research Articles

Developmental plasticity in multimodal signals: light environment produces novel signalling phenotypes in a butterfly.

Developmental plasticity can alter the expression of sexual signals in novel environments and is therefore thought to play an important role in promoting divergence. Sexual signals, however, are often multimodal and mate choice multivariate. Hence, to understand how developmental plasticity can facilitate divergence, we must assess plasticity across signal components and its cumulative impact on signalling. Here, we examine how developmental plasticity influences different components of cabbage white butterfly Pieris rapae multimodal signals, its effects on their signalling phenotypes and its implications for divergence. To do this, we reared P. rapae caterpillars under two different light environments (low-light and high-light) to simulate conditions experienced by P. rapae colonizing a novel light habitat. We then examined plasticity in both visual (wing coloration) and olfactory (pheromone abundance) components of male sexual signals. We found light environments influenced expression of both visual and olfactory components and resulted in a trade-off between signal modalities. The 'low-light' phenotype had duller wing colours but higher abundance of the pheromone, indole, whereas the 'high-light' phenotype had comparatively brighter wings but lower abundance of indole. These results show that by simultaneously altering expression of different signal components, developmental plasticity can produce multiple signalling phenotypes, which may catalyse divergence.

Male and female identity and environmental contexts influence courtship behaviour in a songbird

Behavioural variation in courtship has become a central theme in the study of sexual selection. Courtship behaviour can vary consistently between males (between-individual variation) due to inherent characteristics of individuals, but males may also plastically adjust their courtship (within-individual variation) in response to the characteristics of the potential breeding mate or the environmental contexts. However, the relative importance of these components in courtship behaviour remains poorly understood. Here, we exposed male collared flycatchers, Ficedula albicollis , to different stimulus females simulating a female's visit to the male's territory during mate choice. We measured the male's latency to explicitly invite the female to visit the nestbox (hereafter, invitation latency), as a proxy of the male's motivation to mate. Repeated measurements of focal males (exposed to different stimulus females) and stimulus females (presented to different males) allowed us to assess the relative importance of male and female identity in male courtship, while also assessing the importance of their phenotype and other environmental sources of within-individual variation in invitation latency. We found that invitation latency was determined by male and, to a lesser extent, female identity, with the latter suggesting the existence of male mate choice in the species. We failed to identify specific traits of males and females that influenced courtship behaviour, although male responsiveness to stimulus females increased as the season advanced, possibly due to the costs of delaying breeding in temperate breeding areas. Overall, these results suggest that invitation latency is a consistent courtship attribute in males that can be adjusted plastically according to perceived female quality and environmental conditions. We emphasize that understanding within- and between-individual sources of courtship variation is essential for assessing its evolutionary potential, as plasticity in the expression of sexual signals may affect their reliability and the strength of sexual selection on them. • We simulated female visits to the male's territory and measured courtship. • Courtship behaviour varied consistently between males. • Males adjusted their courtship according to perceived female identity. • Courtship behaviour was also sensitive to seasonality. • Plasticity in sexual signal expression may affect the strength of sexual selection.

Androgen Elevation Accelerates Reproductive Senescence in Three-Spined Stickleback.

Costs of reproduction shape the life-history evolution of investment in current and future reproduction and thereby aging. Androgens have been proposed to regulate the physiology governing these investments. Furthermore, androgens are hypothesized to play a central role in carotenoid-dependent sexual signaling, regulating how much carotenoids are diverted to ornamentation and away from somatic maintenance, increasing oxidative stress, and accelerating aging. We investigated these relationships in male three-spined stickleback in which we elevated 11-ketotestosterone and supplied vitamin E, an antioxidant, in a 2 × 2 design. Androgen elevation shortened the time stickleback maintained reproductive activities. We suspect that this effect is caused by 11-ketotestosterone stimulating investment in current reproduction, but we detected no evidence for this in our measurements of reproductive effort: nest building, body composition, and breeding coloration. Carotenoid-dependent coloration was even slightly decreased by 11-ketotestosterone elevation and was left unaffected by vitamin E. Red coloration correlated with life expectancy and reproductive capacity in a quadratic manner, suggesting overinvestment of the individuals exhibiting the reddest bellies. In contrast, blue iris color showed a negative relationship with survival, suggesting physiological costs of producing this aspect of nuptial coloration. In conclusion, our results support the hypothesis that androgens regulate investment in current versus future reproduction, yet the precise mechanisms remain elusive. The quadratic relationships between sexual signal expression and aspects of quality have wider consequences for how we view sexual selection on ornamentation and its relationship with aging.

Social and abiotic factors differentially affect plumage ornamentation of young and old males in an Australian songbird

Both abiotic environmental conditions and variation in social environment are known to impact the acquisition of sexual signals. However, the influences of abiotic environmental and social factors are rarely compared to each other. Here we test the relative importance of these factors in determining whether and when male red-backed fairy-wrens, Malurus melanocephalus , moult into ornamented breeding plumage , a known sexual signal. One-year-old male red-backed fairy-wrens vary in whether or not they acquire ornamentation, whereas males age 2 years and older vary in their timing of ornament acquisition. It is unclear whether these processes are determined by the same or different factors, and we examined both events using a combination of long-term breeding records and nonbreeding social networks. We found that 1-year-old males that paired prior to the start of the breeding season were more likely to acquire ornamented plumage, but rainfall did not influence whether 1-year-old males acquired ornamented plumage. Thus, for young individuals, social cues appear to play a larger role than abiotic environmental factors in determining ornament acquisition. For older males, timing of ornamented plumage acquisition was constrained by rainfall, with drier nonbreeding seasons leading to poorer physiological condition and later moult dates. Thus, sexual signal variation in older males appears to be a condition-dependent trait, driven by abiotic environmental and physiological factors rather than social cues. These findings reveal that factors influencing sexual signal expression can vary with age when age classes exhibit different forms of signal variation. Our results suggest that social environment may drive sexual signal variation in young individuals, whereas abiotic environmental variation may drive sexual signal variation in older individuals. • The factors influencing sexual signal expression remain unclear. • Social factors determined whether 1-year-old males acquired ornamented plumage. • Rainfall determined when older males acquired ornamented plumage. • Factors influencing sexual signal expression can vary with age.

Wildfire affects expression of male sexual plumage through suppressed testosterone circulation in a tropical songbird

Natural disturbances like drought and wildfires are expected to increase in prevalence, so understanding how organisms are affected is a key goal for conservationists and biologists alike. While many studies have illustrated long‐term effects of perturbations on survival and reproduction, little is known of short‐term effects to physiology and sexual signal expression. Ornamental traits have been proposed as reliable indicators of environmental health, yet studies are lacking in the context of natural disturbances. Here we present short‐term (7–65 days) responses of male red‐backed fairywrens Malurus melanocephalus to wildfire near the onset of the typical breeding season. Young males of this species are characterized by plastic expression of sexual plumage phenotypes depending on circulating testosterone and body condition. Using two populations with fairywren captures before and after separate wildfires we illustrate that wildfire suppressed molt into ornamented plumage. Neither baseline plasma corticosterone or furcular fat stores were affected by fire. However, fire seemed to interfere with the termporal increase in plasma testosterone during the pre‐breeding season, leading to a lower proportion of males molting into ornamented plumage. Collectively, these findings suggest that wildfires inhibit or greatly delay acquisition of ornamentation in males through enduring suppression of testosterone circulation.

Different underlying mechanisms drive associations between multiple parasites and the same sexual signal

Associations between parasite loads and sexual signal expression have long been the focus of research. However, our understanding of how sexual selection operates in the context of multiple parasite infections within the same host is still quite limited. We examined the expression of plumage coloration, which is sexually selected in North American barn swallows, Hirundo rustica erythrogaster , and tail streamer length, which is sexually selected in other barn swallow subspecies, in the context of eight different parasite infections. We found that two parasites, nest mites and Plasmodium , were associated with colour expression, but in opposite directions. Attractive males were less likely to have mites in their nests, but more likely to be infected with Plasmodium . We found that different underlying mechanisms were generating the links between these different parasites and the same colour signal. Males that invested more in colour expression were less likely to survive when infected with Plasmodium , suggesting a physiological mechanism linking colour to Plasmodium infections. However, we found no clear cost to males when examining nest mites, which primarily infect offspring. Instead, using experimental mite manipulations, we provide evidence for a behavioural mechanism, where territorial behaviour and male–male competition likely drive the association between colour expression and nest mite infections. We did not find associations between parasites and streamer length in this subspecies, suggesting that the links between divergent sexual signals and parasites may be quite flexible. These results suggest that the evolution of a single sexual signal can be shaped by several, even opposing, links with different parasite infections. • We examined associations between plumage colour and parasite loads in barn swallows. • Darker males had fewer nest mites but greater likelihood of Plasmodium infection. • Colour investment decreased survival when males were infected with Plasmodium. • Territorial behaviour likely drives colour expression–nest mite association. • Sexual signal evolution can be shaped by different links with multiple parasites.

When night never falls: female sexual signalling in a nocturnal insect along a latitudinal gradient

The environment can play an important role in animal communication by affecting signal transmission and detection. Variation in the signalling environment is expected to be especially pronounced in widely distributed species, potentially affecting how their signals are detected. Such environmental variability is presumably relevant for sedentary females of a nocturnal capital breeder, the European common glow-worm (Lampyris noctiluca), which produce green light during the night to attract flying males to mate. Being widely distributed in Europe, glow-worm populations are exposed to both rapidly descending, darker summer nights in the south, and slowly dimming, brighter summer nights further north, with the latter potentially posing challenges to the visibility of the female glow. To test how female signalling is affected by latitude, we sampled glowing females during summer nights along a latitudinal gradient in Finland, Northern Europe, and used a novel apparatus to measure the intensity and peak wavelength (hue/colour) of their glow. Surprisingly, females at higher latitudes, similar to those at lower latitudes, were commonly glowing during the brightest (and hence the shortest) nights of the year. Females also glowed brighter in more northern areas, partly due to their larger body size, whereas the colour of their glow was not associated with latitude. Since females glow even during midsummer, independent of latitude, the increase in glow intensity at higher latitudes presumably serves to maintain signal visibility in brighter signalling conditions. Overall, these findings highlight the influence of environmental conditions on the evolution of sexual signals, especially in the context of species distribution range.Significance statementWhen environmental conditions impact signal transmission and perception, local conditions can have a crucial role in shaping animal communication and signal evolution. To analyse how dark-dependant common glow-worm females cope with variable nocturnal light environments, we used a novel apparatus, presumably not applied to living animals before, to measure female glow intensity at various latitudes along a latitudinal gradient. Interestingly, females did not avoid signalling during the brightest summer nights, but instead, their glow intensity and body size both increased with latitude. These findings suggest that females can ensure visibility to mate-searching males over a range of local conditions. Our study therefore shows how females can adapt to environmental constraints on signal visibility, and how the expression of sexual signals is shaped not only by social interactions but also by the signalling environment.

Male rock lizards may compensate reproductive costs of an immune challenge affecting sexual signals

AbstractSexual signals can be evolutionarily stable if they are condition dependent or costly to the signaler. One of these costs may be the trade-off between maintaining the immune system and the elaboration of ornaments. Experimental immune challenges in captivity show a reduction in the expression of sexual signals, but it is not clear whether these detrimental effects are important in nature and, more importantly, whether they have reproductive consequences. We designed a field experiment to challenge the immune system of wild male Carpetan rock lizards, Iberolacerta cyreni, with a bacterial antigen (lipopolysaccharide). The immune challenge decreased relative reflectance of ultraviolet structural and melanin-dependent sexual coloration in the throat and the lateral ocelli, whereas the carotenoid-dependent dorsal green coloration was not affected. Immune activation also decreased proportions of ergosterol and cholesta-5,7-dien-3-ol in femoral secretions. These results support a trade-off between the immune system and both visual and chemical sexual ornaments. Moreover, the reproductive success of males, estimated with DNA microsatellites, depended on the expression of some color and chemical traits. However, the immune challenge did not cause overall differences in reproductive success, although it increased with body size/age in control but not in challenged males. This suggests the use of alternative reproductive strategies (e.g., forced matings) in challenged males, particularly in smaller ones. These males might consider that their survival probabilities are low and increase reproductive effort as a form of terminal investment in spite of their “low-quality” sexual signals and potential survival costs.

Attractive male sticklebacks carry more oxidative DNA damage in the soma and germline.

Trade-offs between the expression of sexual signals and the maintenance of somatic and germline tissues are expected when these depend upon the same resources. Despite the importance of sperm DNA integrity, its trade-off with sexual signalling has rarely been explored. We experimentally tested the trade-off between carotenoid-based sexual coloration and oxidative DNA damage in skeletal muscle, testis and sperm by manipulating reproductive schedule (early vs. late onset of breeding) in male three-spined sticklebacks. Oxidative DNA damage was measured as the amount of 8-hydroxy-2-deoxyguanosine in genomic DNA. Irrespective of the experimentally manipulated reproductive schedule, individuals investing more in red coloration showed higher levels of oxidative DNA damage in muscle, testis and sperm during the peak breeding season. Our results show that the expression of red coloration traded off against the level of oxidative DNA damage possibly due to the competing functions of carotenoids as colorants and antioxidants. Thus, female sticklebacks may risk fertility and viability of offspring by choosing redder, more deteriorated partners with decreased sperm DNA integrity. The evolution of sexual signal may be constrained by oxidative DNA damage in the soma and germline.

Sexual Incentive and Choice

In the present manuscript, we review the most important sexual cues in rodents and mammals that influence mate choice. Sexual cues lead to the approach and selection of a partner. In both sexes, hormone levels play an important role by increasing the sensitivity towards the sexual signals emitted by the potential partners and determining the expression of sexual signals that allows the potential partner or intra-sexual competitor to identify the reproductive status. Similarly, sexual cues emitted by both sexes can modify the hormonal status of the potential partner or intra-sexual competitors, so that they can be better skilled reproductively for sexual competition. Future research should analyze the impact of the use of hormonal contraceptives, since it has been shown that they alter the sexual signals emitted and could influence the selection of partners in humans. In addition, this review will be important for anyone using a rodent model to understand sexual motivation.

Sex and seasonal differences in mRNA expression of estrogen receptor α (ESR1) in red-sided garter snakes (Thamnophis sirtalis parietalis)

Estrogens are important regulators of reproductive physiology including sexual signal expression and vitellogenesis. For the regulation to occur, the hormone must bind and activate receptors in target tissues, and expression of the receptors can vary by sex and/or season. By simultaneously comparing circulating hormone levels with receptor expression, a more complete understanding of hormone action can be gained. Our study species, the red-sided garter snake (Thamnophis sirtalis parietalis), provides an excellent opportunity to study the interaction between sex steroid hormones and receptor expression in addition to sexual dimorphism and seasonality. During the spring mating season, male garter snakes rely exclusively on the female’s skin-based, estrogen-dependent sex pheromone to direct courtship. Males can be stimulated to produce this sexual attractiveness pheromone by treatment with estradiol (E2), which also induces male vitellogenesis. Estrogen receptors (ESRs) are required to transduce the effects of estrogens, thus we used quantitative RT-PCR to analyze expression of ESR alpha (ERα; gene ESR1) mRNA in the skin and liver of wild caught male and female garter snakes across simulated spring and fall conditions in the laboratory. While ESR1 was present in the skin of both sexes, there were no sex or seasonal differences in expression levels. Liver expression of ESR1, however, was sexually dimorphic, with females showing greatest expression in fall when circulating E2 concentrations were lowest. There were no statistically significant correlations between E2 and ESR1 expression. Our data suggest that the skin of both sexes is sensitive to estrogen signaling and thus the production of sex pheromone is dependent on bioavailable levels of E2. Female expression of ESR1 in the liver may increase in the fall to prime energy storage mechanisms required for vitellogenesis the following year.

Predation cost of a sexual signal in the threespine stickleback

Lay SummaryThe factors that limit sexual signal expression and ensure honest signaling of mate quality are poorly known. We show that predation risk is a cost of the sexually selected red coloration of the threespine stickleback and, hence, could contribute to signal honesty. A common predator selectively preys on colorful stickleback males in the field, and an experimental study showed that the bright coloration attracts the predator independent of the behavior of the male.

When limited availability of data meets with a thorough meta-analysis: a comment on Moore et al.

On the basis of a systematic literature survey, Moore et al. (2016) have reviewed correlative evidence for the relationship between the expression of sexual signals and stress response. They have identified 38 published studies on 26 species reporting 118 effect sizes for the focal relationship that were entered in a phylogenetic metaanalysis. The analysis failed to derive a general support for the hypothesis that males (or females) with more elaborate traits would experience different stress regimes at the metabolic level than conspecifics with smaller traits. Although Moore et al. (2016) elegantly applied a modern statistical approach, I suggest that the inferences that can be made from their study are limited due to the scarcity of data that are currently available to test the underlying hypothesis. Below, I point to 3 issues to consider for the interpretations of the meta-analytic results. First, the available sample sizes correspond to a statistical power that allow identifying significant associations for very strong effects only. Although Moore et al. (2016) relied on more than 100 effect sizes, these were largely nonindependent. The variation in the predictor variables typically resided on the betweenstudy or between-species levels; thus, the degrees of freedom that were associated with most of the meta-regression tests were determined by the number of studies/species (and not by the number of effect sizes). As a result, most of the effect size estimates were derived with a considerably broad confidence interval (see Table 2 in Moore et al. 2016), which incurs the risk that a biologically meaningful association with smaller effect size remains undetected in a null hypothesis–testing framework. However, for biological reasons, it is expected that most of the relationships would fall into weak to intermediate effect size ranges (sensu Cohen 1988). This is because the focal traits (both physiological measure of stress and sexual traits) are measured with error, and the causal relationship between them, if one exists, is indirect (i.e., mediated by immune suppression or body condition) and involves other physiological/behavioral components (i.e., testosterone levels, escape behaviors). These confounding factors likely set up an upper limit for the strength of the correlations, well below the magnitude of large effect sizes that can be detected between the studied traits. The underlying dataset of Moore et al. (2016) does not have an appropriate statistical power to cope with the biologically expected range of effect sizes. Second, the relationship between the focal traits is complex, may involve nonlinear associations, and be mediated by different mechanistic routes that are difficult to handle statistically given the available sample sizes (and degrees of freedom). For example, as the authors also mention, completely different rules might be applied for the relationship between call rate and glucocorticoid levels in a toad species than for the relationship between repertoire size and levels of heat-shock proteins in a bird species. Furthermore, it would be desirable to distinguish between mechanisms due to baseline stress levels and stress response and to consider confounding effects that are mediated by the ecology of species (Moore et al. 2016). To investigate such complex associations, statistical models that include higher level of interactions between the fixed effects and consider additional potentially confounding variables would be needed. Currently, the limited sample size precludes modeling complex biological mechanisms. Third, at low sample sizes, the problems imposed by influential data points are more emphasized. A careful inspection of the single significant result that has been found in the study (the difference in mean effect size across different types of sexually selected traits) was caused by a single species. This species is the human, which has a distinguished phylogenetic position and the only species that falls in the “opposite sex preference” category. It is therefore likely that the exclusion of this species/category would change the results, and such sensitivity would limit considerably what can be generalized from the current data. In summary, Moore et al. (2016) investigate a timely question in behavioral ecology by summarizing currently available evidence in a thorough meta-analysis. However, the data that have been accumulated on the topic to date are so limited that they undermine any conclusions that can be made from their systematic review. When more data become available, the approach of Moore et al. (2016) will be a straightforward way to follow.

Stress and sexual signaling: a systematic review and meta-analysis

The vertebrate stress response has been shown to suppress investment in reproductive and immune function and may also lead to a reduced investment in the production of secondary sexual traits. However, it has been difficult to model roles of stress in sexual selection due to the inconsistent results seen in empirical studies testing for the effect of stress on the expression of secondary sexual traits. We conducted a phylogenetically controlled meta-analysis of published associations between physiological correlates of stress and sexual signaling in vertebrates in order to identify any consistent patterns. Our analysis included signaling in both males and females, 4 stress measures, and 4 categories of sexually selected traits (vocalizations, traits that varied in size, traits that varied in coloration, and opposite-sex preference). Across 38 studies of 26 species, there was no significant relationship between physiological correlates of stress and the expression of sexual signals. Mean effect size, however, varied significantly across the 4 types of sexually selected trait. We propose development of a model that incorporates the nuanced effects of species ecology, trait type, ecological context, and the complex nature of the physiological stress response, on the expression of sexually selected traits.

Expression of multiple sexual signals by fathers and sons in the East-Mediterranean barn swallow: are advertising strategies heritable?

The level of expression of sexually selected traits is generally determined by genes, environment and their interaction. In species that use multiple sexual signals which may be costly to produce, investing in the expression of one sexual signal may limit the expression of the other, favoring the evolution of a strategy for resource allocation among signals. As a result, even when the expression of sexual signals is condition dependent, the relative level of expression of each signal may be heritable. We tested this hypothesis in the East-Mediterranean barn swallow (Hirundo rustica transitiva), in which males have been shown to express two uncorrelated sexual signals: red-brown ventral coloration, and long tail streamers. We show that variation in both signals may partially be explained by age, as well as by paternal origin (genetic father-son regressions), but that the strongest similarity between fathers and sons is the relative allocation towards one trait or the other (relative expression index), rather than the expression of the traits themselves. These results suggest that the expression of one signal is not independent of the other, and that genetic strategies for resource allocation among sexual signals may be selected for during the evolution of multiple sexual signals.

Immunocompetence handicap hypothesis in tree frog: trade-off between sexual signals and immunity?

The immunocompetence handicap hypothesis (ICHH) assumes that testosterone plays a dual role in mediating both sexual signal expression and immunosuppression. Although there is good evidence of the ICHH in birds, it was primarily tested using only one sexual signal approach. By focusing on the European tree frog Hyla arborea, a species for which mate choice is based on both acoustic and visual signals, we test for the first time the ICHH in a multimodal communication system. The ICHH may be viewed as a universal way to explain signal honesty no matter the sensory modality used by animals. After studying the effects of testosterone on the acous- tic and visual sexual signals through a daily testosterone supplementation, the effects of androgen on the immune system response were measured through a phytohaemagglutinin injection. In H. arborea, we demonstrate that both the acoustic and visual sexual sig- nals were testosterone dependent. However, the phytohaemagglutinin injection did not provoke immunosuppression for testosterone- supplemented males. Surprisingly, the testosterone-supplemented males with a high body mass presented an immunoenhancement. Therefore, it seems that ICHH is not an integrating mechanism that is able to explain signal honesty in the multimodal signaling system used by H. arborea in mate choice. On the contrary, our results support the idea that multiple mechanisms (e.g., cost-added and index signals) operating simultaneously may explain signal honesty of both acoustic and visual signals.

A novel mechanism regulating a sexual signal: The testosterone-based inhibition of female sex pheromone expression in garter snakes

Vertebrates communicate their sex to conspecifics through the use of sexually dimorphic signals, such as ornaments, behaviors and scents. Furthermore, the physiological connection between hormones and secondary sexual signal expression is key to understanding their dimorphism, seasonality and evolution. The red-sided garter snake (Thamnophis sirtalis parietalis) is the only reptile for which a described pheromone currently exists, and because garter snakes rely completely on the sexual attractiveness pheromone for species identification and mate choice, they constitute a unique model species for exploring the relationship between pheromones and the endocrine system. We recently demonstrated that estrogen can activate female pheromone production in male garter snakes. The purpose of this study was to determine the mechanism(s) acting to prevent female pheromone production in males. We found that castrated males (GX) are courted by wild males in the field and produce appreciable amounts of female sex pheromone. Furthermore, pheromone production is inhibited in castrates given testosterone implants (GX+T), suggesting that pheromone production is actively inhibited by the presence of testosterone. Lastly, testosterone supplementation alone (T) increased the production of several saturated methyl ketones in the pheromone but not the unsaturated ketones; this may indicate that saturated ketones are testosterone-activated components of the garter snake's skin lipid milieu. Collectively, our research has shown that pheromone expression in snakes results from two processes: activation by the feminizing steroid estradiol and inhibition by testosterone. We suggest that basal birds and garter snakes share common pathways of activation that modulate crucial intraspecific signals that originate from skin.

Multimodal Sexual Signaling and Mating Behavior in Olive Baboons (Papio anubis)

In primate species, mating decisions seem to be based on multiple signal elements with different roles in the signaling of female reproductive status. Whereas some primate signals are relatively well described (e.g., sexual swellings and copulation calls), studies that simultaneously assess visual, auditory, behavioral, and olfactory cues as signals of reproductive state are rarely undertaken. We used data on variation in sexual behaviors and sexual swellings in relation to the fertile period (estimated from the date of swelling detumescence) from a troop of semi-free ranging olive baboons (Papio anubis) to assess how different signals influence patterns of mate choice. Using an objective and quantitative measure of swelling size and color, along with detailed data on sexual behaviors from 13 cycles of nine adult females, we found that fine-scale variation in sexual swelling size, female behavior and copulation call rates could advertise the beginning of the fertile phase whereas swelling color did not. Rates of olfactory inspections by males also increased during the fertile phase, suggesting that olfactory signals were of interest to males and may contain information about ovulation. There was no relationship between female characteristics (age and rank) and the expression of sexual signals, except for proceptive behaviors which increased with female rank. Males displayed more sexual behaviors such as approaches and holding and tended to direct more ejaculatory mounts during the fertile phase. All together, we suggest that whereas all males could have information concerning the timing of ovulation through female proceptive behaviors and swelling size, consorting males may have access to additional signals (olfactory cues). Sexual communication in olive baboons is consistent with a multimodal framework for fertility signaling, potentially allowing males and females to establish different mating strategies. The possible selective pressures leading to multi-modal signaling are discussed.

Body condition influences sexual signal expression independent of circulating androgens in male red-backed fairy-wrens

Androgens play a major role in the regulation of sexual signal expression of male vertebrates. In this study we assessed the prevalent, yet largely untested, assumption that signal honesty is maintained through condition-dependent androgen regulation by experimentally manipulating body condition of male red-backed fairy-wrens (Malurus melanocephalus) through trimming several flight feathers before the prenuptial molt. In their first reproductive season males of this species exhibit androgen-regulated plasticity in plumage coloration, ranging from red/black (high androgens) to brown (low androgens). Red/black plumage is preferred by females and might be constrained by a negative relationship between body condition and androgen levels. We also evaluated whether corticosterone changes to altered conditional state mediate the relationship between condition and androgens. While we predicted that males with trimmed feathers would expend greater energy and thus be in poorer condition at the time of molt, they were counter-intuitively in better condition compared to control birds, likely as a consequence of subtle behavioral changes. These birds in better condition molted a greater proportion of red/black plumage, as predicted, and also molted more heavily. However, experimental and control birds did not differ in their androgen or corticosterone concentrations. Furthermore, analysis of long-term data from the same population revealed no correlation between condition and androgen levels. Collectively, these results challenge the notion that condition-dependent androgen regulation alone is responsible for maintaining the honesty of sexual signals and highlights the necessity of considering alternate explanations.

Social context decouples the relationship between a sexual ornament and testosterone levels in a male wild bird

In order to maximise fitness individuals should adjust their level of signalling according to their surrounding social environment. However, field experiments showing such adjustment of current signalling associated to changes in social context are lacking. Here, we manipulated levels of male aggressive- and dominance-related displays in a wild bird in our treated area by increasing testosterone levels using implants in a subset of males. We then compared the expression of sexual signals (i.e. comb size) between non-treated red grouse Lagopus lagopus scoticus males from control and treatment areas. We further explored the potential endocrinological mechanism linking social environment and signal expression by analysing testosterone levels in all males. Our treatment successfully increased overall aggressive- and dominance-related behaviours in the treatment area. Furthermore, testosterone-implanted birds increased their comb size as repeatedly shown in previous studies in male red grouse. Interestingly, untreated males living in the treatment area decreased their comb size, whilst increasing testosterone levels. Since comb size is a signal of dominance, untreated males from the treatment area may have perceived themselves as subordinate individuals and decreased their signalling levels to avoid confrontations with testosterone-treated, dominant individuals. In conclusion, our findings show that social context has the potential to regulate sexual signalling and testosterone levels. Our results highlight the role of social context when exploring the link between testosterone and behaviour, as it may reverse the relationship between both traits. Our results suggest that social context affects signalling and testosterone independently.