High brood patch temperature of less colourful,less pheomelanic female Barn Swallows Hirundo rustica

In birds, even a minor difference in egg temperature (1–1.5 °C) has been shown to affect the fitness of offspring by changing hatching success, incubation period and nestling quality. Female, but not male, passerines develop brood patches. Thus if there are traits, such as plumage ornamentation, that indicate optimal egg temperature, males should pair with females that exhibit those traits. However, no study has yet investigated the relationship between female brood patch temperature, which would directly affect egg temperature, and female plumage ornamentation. In this study, we examined the surface temperature of female brood patches during nocturnal incubation and examined its relationship with female plumage ornaments in Asian Barn Swallows Hirundo rustica gutturalis. After controlling for ambient air temperature, brood patch temperature was negatively associated with colour saturation of the female throat patch. No other female ornaments, such as tail‐length, white tail spots or throat patch size, predicted brood patch temperature. When oral (mouth) temperature was statistically controlled, females with less colourful throats and longer tails showed higher brood patch temperature, indicating that these females had hotter brood patches in relation to the temperature of other body parts. Furthermore, we found a negative relationship between pheomelanin pigmentation and brood patch temperature after controlling for ambient air temperature or oral temperature. To our knowledge, this is the first study to show that female ornaments can predict the absolute/relative thermal investment in brood patches. This relationship, together with other aspects of female quality, may affect male mate preference and female ornamentation.     

The role of functional constraints in nonrandom mating patterns for a dance fly with female ornaments

Most hypotheses to explain nonrandom mating patterns invoke mate choice, particularly in species that display elaborate ornaments. However, conflicting selection pressures on traits can result in functional constraints that can also cause nonrandom mating patterns. We tested for functional load‐lifting constraints during aerial copulation in Rhamphomyia longicauda, a species of dance fly that displays multiple extravagant female‐specific ornaments that are unusual among sexual traits because they are under stabilizing selection. R. longicauda males provide females with a nuptial gift before engaging in aerial mating, and the male bears the entire weight of the female and nuptial gift for the duration of copulation. In theory, a male's ability to carry females and nuptial gifts could constrain pairing opportunities for the heaviest females, as reported for nonornamented dance flies. In concert with directional preferences for large females with mature eggs, such a load‐lifting constraint could produce the stabilizing selection on female size previously observed in this species. We therefore tested whether wild‐caught male R. longicauda collected during copulation were experiencing load‐lift limitations by comparing the mass carried by males during copulation with the male's wing loading traits. We also performed permutation tests to determine whether the loads carried by males during copulation were lighter than expected. We found that heavier males are more often found mating with heavier females suggesting that whereas R. longicauda males do not experience a load‐lift constraint, there is a strong relationship of assortative mating by mass. We suggest that active male mate choice for intermediately adorned females is more likely to be causing the nonrandom mating patterns observed in R. longicauda.     

Sexually selected sexual selection: Can evolutionary retribution explain female ornamental colour?

By preferring mates with increasingly costly ornaments or courtship displays, females cause an escalation of male reproductive costs. Such increased costs should promote male selectivity based on fecundity‐linked female attributes, leading to female ornamentation in species with traditional sex roles. Consequently, female ornamentation should evolve more frequently in taxa where male reproduction is costly than in comparable taxa where it is cheaper. We assessed the prevalence of female ornamental colouration in two clades of viviparous cyprinodontid fish: the Goodeinae, where stringent female choice imposes male mating costs, and the Poeciliinae, whose males can circumvent female mate choice. We found that although in the Poeciliinae female ornamental colour is a correlated, but paler version of male coloration, females of the Goodeinae often display vivid ornamental colours that are distinct from those of males. Thus, male and female ornaments are not (phylo)genetically correlated in the Goodeinae. Furthermore, phylogenetic signal on male and female colour is clearly detectable in the Poeciliinae, but absent in the Goodeinae, suggesting that ornamental colour of males and females in the latter may be the consequence of selection. Given that enforceable female choice has promoted male ornaments, we propose that evolutionary retribution has promoted distinct female ornaments in the Goodeinae.     

Experimental trait mismatches uncover specificity of evolutionary links between multiple signaling traits and their interactions in hummingbirds*

Many animal signals co‐occur, and these signals may coevolve due to their interactive properties. Previous work has demonstrated ecological drivers of evolutionary relationships between signals and the environment, which leads to questions about why specific signal pairs evolved among species that possess multiple signals. We asked whether the coloration of different species was optimized for presentation with its natural behavioral display. We investigated this in “bee” hummingbirds, where males exhibit angle‐dependent structurally‐colored plumage and a stereotyped courtship (shuttle) display, by experimentally creating mismatches between the behavior and plumage of five species and quantifying how these mismatches influenced male color appearance during a display. Specifically, we photographed the plumage from a given species as we moved its feathers through the position‐and‐orientation‐specific courtship display path of other species and quantified the resulting color appearance during the display in order to compare the mismatched color appearance to each species’ natural color appearance. We found that mismatches significantly altered display flashiness (% change in coloration during displays) compared to the natural plumage‐behavior pairings, and that such departures in flashiness were predicted by differences in shuttle behaviors alone. These results illustrate a tight evolutionary relationship between shuttle displays and color flashiness in these hummingbirds. Further, we found that interspecific variation in male plumage, behavior, and natural color appearance predicted deviations between natural and mismatched flashy color appearance. Altogether, our work provides a new method for testing signal coevolution and highlights the complex evolutionary relationships between multiple signals and their interactions.     

Colourful traits in female birds relate to individual condition,reproductive performance and male-mate preferences: a meta-analytic approach

Colourful traits in females are suggested to have evolved and be maintained by sexual selection. Although several studies have evaluated this idea, support is still equivocal. Evidence has been compiled in reviews, and a handful of quantitative syntheses has explored cumulative support for the link between condition and specific colour traits in males and females. However, understanding the potential function of females'' colourful traits in sexual communication has not been the primary focus of any of those previous studies. Here, using a meta-analytic approach, we find that evidence from empirical studies in birds supports the idea that colourful female ornaments are positively associated with residual mass and immune response, clutch size and male-mate preferences. Hence, colourful traits in female birds likely evolved and are maintained by sexual selection as condition-dependent signals.     

Me against who? Male guppies adjust mating behaviour according to their rival’s presence and attractiveness

Sexual selection theory suggests that males need to constantly reappraise their mating decisions to take account of the presence and the phenotypes of their rivals. Here we examine this expectation by asking: (i) If the presence of a rival influences male mating behaviour; (ii) How important is the attractiveness of the rival (absolute attractiveness) in shaping male behaviour; and (iii) How does a male's attractiveness in comparison to his rival (relative attractiveness) influence a male's mating decisions. Using the Trinidadian guppy, a species in which female mate choice (based on males’ attractive traits) plays an important role in male mating outcomes, we recorded the frequency of courtship displays and unsolicited attempts by focal males. First, we quantified focal male mating behaviour with and without a rival. Since the probability of a successful mating is, on average, halved by the presence of a rival, we predicted that under competition the focal male would invest more in less costly mating tactic—unsolicited attempts. Second, we examined how the rival's standard length and area of orange coloration mediated focal male mating behaviour. We found that rival presence influenced how focal males responded to females in terms of both mating tactics. However, the rival attractiveness elicited changes only in male courtship display. Focal males increased courtship display rate if his rival was small or if possessed large amounts of orange, regardless of considering rival absolute or relative attractiveness. Our results show that males invest in the costlier mating tactic when there is no rival or in the presence of a smaller rival. Interestingly, they make a similar investment in the presence of an attractive orange rival. Overall, this study highlights the importance of fine‐grained male decisions in mating encounters and shows that mating tactics are differentially shaped by multiple competition risk cues.     

The Association Between Personality Traits,Morphological Traits and Alternative Mating Behaviour in Male Endler's Guppies,Poecilia wingei

Alternative mating behaviour, personality traits and morphological characters are predicted to be correlated. Bolder, larger and more colourful males are expected to preferentially court females, while shy, small and drab‐coloured individuals are predicted to sneak copulations. We used males of Endler's guppy, Poecilia wingei, to test this association over a long temporal period (hence including ontogenetic changes) and under two social environments (male‐biased and female‐biased). We found that personality traits (exploration, boldness, activity) of P. wingei males were highly repeatable across long time spans, but they were not correlated (formed no behavioural syndrome). Male age and social environment had no effect on any personality trait, despite their effects on alternative mating behaviour. Young males with higher activity levels were more likely to attempt sneaking. In older fish, there was an association between orange coloration, courtship and boldness, but this was not observed in young males. Our results suggest that alternative mating behaviour is more flexible than personality traits and is independent of them. Non‐colour‐based morphological traits (gonopodium length, body length, caudal straps length, dorsal fin length) were not correlated with any particular mating behaviour.     

Variation in female mate choice within guppy populations: population divergence,multiple ornaments and the maintenance of polymorphism

The evolutionary significance of variation in mate choice behaviour is currently a subject of some debate and considerable empirical study. Here, I review recent work on variation within and among guppy (Poecilia reticulata) populations in female mate choice and mating preferences. Empirical results demonstrate that there is substantial variation within and among populations in female responsiveness and choosiness, and much of this variation is genetic. Evidence for variation in preference functions also exists, but this appears to be more equivocal and the relative importance of genetic variation is less clear cut. In the second half of this review I discuss the potential significance of this variation to three important evolutionary issues: the presence of multiple male ornaments, the maintenance of polymorphism and divergence in mate recognition among populations. Studies of genetic variation in mate choice within populations indicate that females have complex, multivariate preferences that are able to evolve independently to some extent. These findings suggest that the presence of multiple male ornaments may be due to multiple female mating preferences. The extreme polymorphism in male guppy colour patterns demands explanation, yet no single satisfactory explanation has yet emerged. I review several old ideas and a few new ones in order to identify the most promising potential explanations for future empirical testing. Among these are negative frequency dependent selection, environmental heterogeneity coupled with gene flow, and genetic constraints. Last, I review the relative extent of within and among-population variation in mate choice and mating preferences in order to assess why guppies have not speciated despite a history of isolation and divergence. I argue that variation within guppy populations in mate choice and enhanced mating success of new immigrants to a pool are major impediments to population divergence of the magnitude that would be required for speciation to occur.     

拟环纹豹蛛雄蛛触肢上黑白相间毛饰物的功能

狼蛛科雄蛛附肢上多样化的饰装往往与求偶行为相偶联,这些特殊的饰装通常被认为是雌性选择的结果。拟环纹豹蛛Pardosa pseudoannulata,属狼蛛科豹蛛属,雄蛛触肢胫节密被白毛,跗舟密被黑毛,具有典型的性二型现象;同时,只有成熟的雄蛛才展现触肢黑白相间的毛饰物。推测拟环纹豹蛛雄蛛触肢这种黑白相间的毛饰物可能在物种识别中具重要作用。在室内我们拟通过涂抹操作对拟环纹豹蛛雄蛛触肢黑白相间毛饰物的功能进行分析。实验分为4组,分别是对照组(A组,雄蛛不做任何处理)、雄蛛触肢白色胫节全部涂成黑色(B组)、雄蛛触肢黑色跗舟全部涂成白色(C组)和雄蛛触肢的黑色跗舟被涂成黑色(D组),然后采用雌雄配对进行求偶交配行为测定。实验结果表明,B组雄蛛的交配成功率显著低于A、C和D组的雄蛛,而后3组雄蛛的交配成功率无显著差异。相反,B组雄蛛被雌蛛相食百分率显著高于其它3组。可见拟环纹豹蛛雄蛛触肢上黑白相间毛饰物,尤其是其胫节上的白色饰物在雌蛛种间识别中起重要作用。     

Animal allure and health linked by plant pigments

Darwin introduced the idea that ornamental secondary sexual traits have evolved in response to female preferences for showy males. Among such traits, yellow and red carotenoid-based ornaments have been considered as particularly good candidates for explaining why and how females would benefit from mating with showy partners. Because carotenoids can be used for promotion of both health and appearance, colourful male ornaments should honestly reveal the vigour of the bearers. Two recent experiments with birds now show how allocation of bodily carotenoids to sexual signalling is traded off against the use of carotenoids for boosting immune function.     

Stable correlation structure among multiple plumage colour traits: can they work as a single signal?

The presence of multiple distinct ornamental traits in the same species is frequently explained by context‐specificity and different information content. However, the expression of multiple ornaments is often correlated, and such traits may therefore function as a single, integrated signal. Delayed use of an integrated signal relative to production requires temporal stability in integration, which has seldom been examined. We used autumn and spring reflectance data from the breast, breast stripe, and crown of great tits (Parus major) to assess the stability and mating implications of colour signal integration, as well as the repeatability of any integrated colour trait and its correlation with condition during moult. We found high levels of stability between seasons, years, sexes, and ages in the correlation patterns of colour measures across the three plumage areas. The first principal component colour axis described joint variation of ultraviolet (UV) reflectance on the crown and the breast stripe, thereby representing an among‐trait UV chroma axis. However, only breast yellow chroma showed condition‐dependence, whereas temporally consistent and significant assortative mating was restricted to crown UV chroma. Our results therefore do not support the idea that the overall UV chroma of the breast stripe and the crown is special in condition‐dependence and repeatability, or that it plays a specific role in mutual sexual selection as an integrated signal. The results show that stable association between display traits is an existing phenomenon. They also indicate that, even in the presence of correlated traits, functional trait integration among these requires further scrutiny. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 114 , 92–108.     

The lek mating system of the worm pipefish (Nerophis lumbriciformis): a molecular maternity analysis and test of the phenotype‐linked fertility hypothesis

The origin and maintenance of mating preferences continues to be an important and controversial topic in sexual selection research. Leks and lek‐like mating systems, where individuals gather in particular spots for the sole purpose of mate choice, are particularly puzzling, because the strong directional selection imposed by mate choice should erode genetic variation among competing individuals and negate any benefit for the choosing sex. Here, we take advantage of the lek‐like mating system of the worm pipefish (Nerophis lumbriciformis) to test the phenotype‐linked fertility hypothesis for the maintenance of mating preferences. We use microsatellite markers to perform a parentage analysis, along with a mark–recapture study, to confirm that the worm pipefish has an unusual mating system that strongly resembles a female lek, where females display and males visit the lek to choose mates. Our results show that the most highly ornamented females occupy positions near the centre of the breeding area, and males mating with these females receive fuller broods with larger eggs compared to males mating with less‐ornamented females. We also conduct a laboratory experiment to show that female ornaments are condition‐dependent and honestly signal reproductive potential. Overall, these results are consistent with the predictions of a sex‐independent version of the phenotype‐linked fertility hypothesis, as male preference for female ornaments correlates with fertility benefits.     

Melanin‐based coloration of sneaker male Atlantic salmon is linked to viability and emergence timing of their offspring

The ‘good genes’ hypothesis of sexual selection predicts that male ornaments are favoured by female mate choice because male ornament reveals genetic quality. In species with different male reproductive tactics, variation in genetic quality among ‘sneaking’ males has rarely been investigated, as usually ‘sneakers’ are thought not to be chosen by females. Here we focused on the alternative reproductive tactic in Atlantic salmon (Salmo salar Linnaeus, 1758) to test whether the skin colour of sneakers may reveal the performance traits of their offspring. A fully factorial breeding design was realized between 20 sneakers and two females using in vitro fertilization. We quantified the red and dark colorations of males and measured the survival of their progeny under semi‐natural conditions. In addition, the size of offspring and their emergence timing from the gravel nest were monitored in the laboratory. We found that darker males sired more viable offspring, whereas red coloration was negatively correlated with offspring survival. Nevertheless, darker and redder male pigmentations were linked to a delay in offspring emergence. These results demonstrate that colours can reveal individual genetic quality in an alternative male reproductive tactic, with male melanin‐based coloration being linked to both beneficial and detrimental effects for the offspring. Our results imply that sneaker ornaments may potentially play a role in both intra‐ and intersexual selection. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111 , 126–135.     

Courtship and genetic quality: asymmetric males show their best side

Fluctuating asymmetry (FA), the small random deviations from perfect morphological symmetry that result during development, is ubiquitous throughout the animal kingdom. In many species, FA seems to play a role in mate choice, perhaps because it signals an individual''s genetic quality and health. However, the relationship between an individual''s FA and behaviour is generally unknown: what do more asymmetric individuals do about their own asymmetry? We now show for the first time that individuals respond behaviourally to their own morphological FA in what appears to be an adaptive manner. During courtship, male guppies exhibiting high FA in ornamental colour, bias their displays towards their more colourful body side, thus potentially increasing their attractiveness by exaggerating the quantity of their orange signal. This appears to be a strictly behavioural male response to cues provided by females, as it does not occur when males court a non-reactive model female. Whether inferior males realize any mating advantage remains uncertain, but our study clearly demonstrates a behavioural response to random morphological asymmetries that appears to be adaptive. We propose that the tendency to show or otherwise use a ‘best side’ is common in nature, with implications for sexual signalling and the evolution of more pronounced asymmetries.     

Male sexual ornament size is positively associated with reproductive morphology and enhanced fertility in the stalk-eyed fly <Emphasis Type="Italic">Teleopsis dalmanni</Emphasis>

Background  

Exaggerated male ornaments and displays often evolve in species where males only provide females with ejaculates during reproduction. Although "good genes" arguments are typically invoked to explain this phenomenon, a simpler alternative is possible if variation in male reproductive quality (e.g. sperm number, ejaculate content, mating rate) is an important determinant of female reproductive success. The "phenotype-linked fertility hypothesis" states that female preference for male ornaments or displays has been selected to ensure higher levels of fertility and has driven the evolution of exaggerated male traits. Females of the stalk-eyed fly Teleopsis dalmanni must mate frequently to maintain high levels of fertility and prefer to mate with males exhibiting large eyespan, a condition-dependent sexual ornament. If eyespan indicates male reproductive quality, females could directly increase their reproductive success by mating with males with large eyespan. Here we investigate whether male eyespan indicates accessory gland and testis length, and then ask whether mating with large eyespan males affects female fertility.     

Seasonal colour change by moult or by the abrasion of feather tips: a comparative study

Many birds undergo seasonal changes in plumage coloration by prebreeding moult, abrasion of cryptic feather tips, or both. Seasonal dichromatism is thought to result from optimizing coloration to the conflicting demands of different life-cycle periods, sexual selection for conspicuousness being substantial during the mating season, whereas selection for camouflage and for social signals may act in all seasons. Furthermore, energetic and time demands may constrain the extent of moult, thereby limiting colour change. We investigated the relative importance of several factors in shaping this variation in a songbird clade using phylogenetic comparative methods. We found that prebreeding moult relates most strongly to breeding onset and winter diet, demonstrating that both time and food availability constrain feather replacement. Feather abrasion was best predicted by winter flocking behaviour, and secondarily by open habitats, implying that exposure to predators and the simultaneous need for social signalling may favour the expression of partially obscured ornaments in the non-breeding season. The combined occurrence of prebreeding moult and feather abrasion was associated with the polygynous mating system, suggesting that species under strong sexual selection may employ both strategies of colour change to ensure the full expression of breeding coloration.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 94 , 711–721.     

Male colour variation in a eurytopic African cichlid: the role of diet and hypoxia

Species that cross strong environmental gradients are expected to face divergent selective pressures that can act on sexually‐selected traits. In the present study, we examine the role of hypoxia and carotenoid availability in driving divergence in two sexually‐selected traits, male colour and reproductive behaviour, in the African cichlid Pseudocrenilabrus multicolor victoriae. Low‐dissolved oxygen (DO) (hypoxic) environments are expected to be energetically challenging; given that male nuptial colour expression and courtship displays can be costly, we expected fish in low‐DO versus high‐DO environments to differ in these traits. First, a field survey was used to describe natural variation in male nuptial colour patterns and diet across habitats divergent in DO. Next, using wild‐caught fish from a low‐DO and high‐DO habitat, we tested for differences in reproductive behaviour. Finally, a laboratory rearing experiment was used to quantify the interaction of DO and diet (low‐ versus high‐carotenoid availability) on the expression of male colour during development. In energetically challenging low‐DO environments, fish were more red and, in high‐DO environments, fish were typically brighter and more yellow. The frequency of reproductive displays in fish of low‐DO origin was 75% lower, although this had no consequence for brooding frequency (i.e. both populations produced the same number of broods on average). Our laboratory rearing study showed carotenoid availability to be important in colour production with no direct influence of DO on colour. Additionally, weak patterns of diet variation across wild populations suggest that other factors in combination with diet are contributing to colour divergence.     

Unravelling the evolution of complex reproductive traits with phenotypic engineering

The social dynamics surrounding courtship, mating and parental care are complex enough when just a single male and female are involved, but for species that employ multiple strategies for achieving fertilization success, the network of interactions among rivals, allies and suitors can be utterly complicated. Such is the case in the ocellated wrasse, Symphodus ocellatus, in which males adopt one of three mating strategies. The large, colourful “nesting males” court females, defend territories and care for fertilized eggs until they hatch. The smaller “satellite males” help the nesting males court females and guard against the third morph, the “sneaker males”, which sneak in when a nesting male is spawning with a female and surreptitiously release sperm. Sneaker males perform no courtship displays nor defend territories, so their reproductive investment is devoted entirely to sperm production. And these alternative male strategies work: 100% of nests contain some eggs fertilized by sneaker and satellite males, despite the fact that parental care is solely the responsibility of nesting males In this issue of Molecular Ecology, work to untangle the proximate mechanisms regulating the reproductive physiology of nesting males and their behaviour towards other males, which impacts the entire social network. Moreover, they describe how variation in neuroendocrine regulation can give rise to variation in reproductive traits, upon which sexual selection can act.     

INTRASEXUAL COMPETITION ALONE FAVORS A SEXUALLY DIMORPHIC ORNAMENT IN THE RUBYSPOT DAMSELFLY HETAERINA AMERICANA

I studied the sex-limited red spots on the wings of male rubyspot damselflies (Hetaerina americana) in relation to territoriality and fitness in the wild. Both observational and experimental (wing spot manipulation) studies indicated that wing spots were selected through competition among males for mating territories, not through female choice or direct competition for females. Males with naturally or artificially large wing spots were more successful at holding territories and consequently mated at higher rates than males with relatively small wing spots. In contrast, sexual selection on male body size appeared to operate among nonterritorial males at the clasping stage of the mating sequence, perhaps because larger males were better at clasping females forcibly. Of four models proposed to explain the evolution of ornaments through territory competition, only the agonistic handicap model makes predictions consistent with the results of this study.     

Female dimorphism and mating behaviour in a damselfly, Ischnura ramburi: females mimicking males

Females of the damselfly Ischnura ramburi exhibit a simple genetic colour dimorphism in which one form is cryptic (heteromorph), and the other closely resembles the more conspicuously colourful males (andromorph). Andromorphs also mimic male behaviour in interactions with males. Consequently they copulate half as often as do heteromorphs, which may give them a frequency-dependent selective advantage. Assuming that females need only mate once, excessive copulations, which average 3 h in duration, waste time for heteromorphs and may expose them to increased predation. The peculiar biology and mating behaviour of ischnurans provides a possible evolutionary context for this mimicry. The polymorphism is probably balanced by a frequency-independent selective disadvantage suffered by the more conspicuous andromorphs, through increased predation.