Egg Colour Covaries with Female Expression of a Male Ornament in the Spotless Starling (Sturnus unicolor)

The sexually selected egg colour hypothesis (SSECH) proposes that egg colouration is as a post-mating sexually selected signal of female phenotypic quality, maintained by a higher allocation of paternal care. Similarly, some female traits can reflect genetic quality or condition and males could use this information in mate choice or in modulating parental investment. In our study, we examined the correlation of individual variation in egg colouration with female expression of a male ornament and how male feeding covaried with these two female traits in the spotless starling, in which egg colour varies widely between clutches and where both sexes possess showy throat feathers that are age dependent and that may signal individual quality. According to the SSECH, high-quality females (females with longer throat feathers) are expected to lay more colourful eggs than low-quality females and males should modify their feeding behaviour accordingly. By means of a principal component analysis, we found that most of the variation in egg colouration was due to brightness differences, and in a lower proportion to chromatic variation. Chromatic variation reflected a ultraviolet (UV) vs. greenness trade-off and was positively associated with throat feather length: females with larger throat feathers laid eggs with higher UV and lower green reflectance. However, egg brightness was not related to female feather length, as the SSECH would predict. Male feedings were positively related to female throat feather length and negatively related to chromatic variation, meaning that males contributed more to nests of females with long throat feathers who laid eggs with higher UV and lower green reflectance. In conclusion, our data provide mixed support for the SSECH: although egg chromatic variation was related to female expression of a male ornament and male parental care, we found no evidence that egg brightness was involved in these processes.     

Ultra-violet reflectance of male and female red grouse, Lagopus lagopus scoticus, sexual ornaments reflect nematode parasite intensity

In many birds, females prefer males with the biggest or brightest sexual ornaments, which might reflect a higher phenotypic quality, such as fewer parasites. Unlike humans, most birds detect near-ultraviolet (UV) light, and UV signals can play an important role in sexual signalling and mate choice. Using a spectrophotometer, we analysed the colour of red grouse Lagopus lagopus scoticus sexual ornaments (their combs). We first show that combs reflect both in the red (600–700 nm) and UV (300–400 nm) part of the spectrum. Second, we investigated whether comb size and colour, and UV reflectance in particular, reflected an aspect of individual quality: the intensity of infection by a main nematode parasite, the caecal threadworm Trichostrongylus tenuis . We first analysed comb size and colour variation, and parasite intensity variation, in relation to sex and age. Males had bigger and redder combs than females, but UV brightness was greater for female than for male combs. Comb colour also differed between age groups, with young birds of both sexes showing brighter UV than old birds. Young grouse also had fewer T. tenuis worms than old grouse. We further tested whether intensity of infection could be predicted from comb characteristics (size and colour) in male and female red grouse. We found that parasite intensity was not significantly related to comb size or red brightness, but fewer worms were predicted from brighter UV in combs, in both males and females. The results indicate that UV reflectance of combs have a quality revealing function and might play an important role in grouse mate choice: UV brightness of combs could enable both male and female red grouse to assess the parasite loads of a potential mate.     

The role of colour in signalling and male choice in the agamid lizard Ctenophorus ornatus

Bright coloration and complex visual displays are frequent and well described in many lizard families. Reflectance spectrometry which extends into the ultraviolet (UV) allows measurement of such coloration independent of our visual system. We examined the role of colour in signalling and mate choice in the agamid lizard Ctenophorus ornatus. We found that throat reflectance strongly contrasted against the granite background of the lizards' habitat. The throat may act as a signal via the head-bobbing and push-up displays of C. ornatus. Dorsal coloration provided camouflage against the granite background, particularly in females. C. ornatus was sexually dichromatic for all traits examined including throat UV reflectance which is beyond human visual perception. Female throats were highly variable in spectral reflectance and males preferred females with higher throat chroma between 370 and 400 nm. However, female throat UV chroma is strongly correlated to both throat brightness and chest UV chroma and males may choose females on a combination of these colour variables. There was no evidence that female throat or chest coloration was an indicator of female quality. However, female brightness significantly predicted a female's laying date and, thus, may signal receptivity. One function of visual display in this species appears to be intersexual signalling, resulting in male choice of females.     

Effect of UV-reflecting markings on female mate-choice decisions in Cosmophasis umbratica, a jumping spider from Singapore

Earlier studies have shown that Cosmophasis umbratica, a jumpingspider from Singapore, is sexually dimorphic in the reflectanceof ultraviolet (UV) (males, but not females, have UV-reflectingmarkings). Here we present the first experimental evidence thatthe male's UV markings influence mate choice of C. umbraticafemales. When presented with males whose appearance was manipulatedby the use of a UV-blocking filter, females spent more timewatching UV+ males (i.e., males with UV present) and less timewatching UV– males (UV absent). We also manipulated thelevels of male brightness by using 2 UV-transmitting neutraldensity filters and showed that UV reflectance was used specificallyfor hue discrimination instead of being used for detecting differencesin brightness alone. This is not only the first strong evidenceof UV influence on female mate-choice decisions for a spiderbut also the best experimental demonstration of color vision,whatever the wavelength.     

Structural plumage colour and parasites in satin bowerbirds Ptilonorhynchus violaceus: implications for sexual selection

We investigated whether variation in structural plumage coloration in satin bowerbirds, Ptilonorhynchus violaceus , could reveal the intensity of infection from parasites, as predicted from models of parasite-mediated sexual selection (PMSS). To do this, we captured adult male, female, and juvenile male satin bowerbirds in Queensland, Australia, and objectively measured individual plumage reflectance from four body regions using a spectrometer. We quantified both ectoparasite load and the intensity of infection from blood parasites. In iridescent blue adult males, plumage reflectance is unimodal, with a single peak in the ultraviolet, while in greenish females and juveniles, plumage reflectance is bimodal, with peaks in both the ultraviolet and green portions of the spectrum. In adult males, the intensity of infection from blood parasites was best predicted by plumage brightness (total reflectance), with brighter males having fewer parasites. Similarly, juvenile males exhibiting greater UV chroma (proportion of reflectance in the UV) had fewer blood parasites. Our findings support a key prediction of PMSS models and provide the first evidence that a structural colour ornament can signal the intensity of infection from blood parasites.     

Ultraviolet plumage ornamentation affects social mate choice and sperm competition in bluethroats (Aves: Luscinia s. svecica): a field experiment

The blue throat feathers of male bluethroats (Luscinia s. svecica) show a reflectance peak in the ultraviolet (UV) waveband (320 to 400 nm). The throat is actively displayed during courtship, suggesting a role for sexual selection on an ultraviolet signal. Indeed, a recent aviary experiment demonstrated that females discriminated against males with artificially reduced UV reflectance (Andersson and Amundsen 1997). Here, we report the results of a similar experimental manipulation applied on free-ranging males. UV-reduced (UVR) males had a lower success in attracting mates, as judged from a significantly later start of egg laying, compared with control (C) males. UVR males also spent significantly less time advertising for additional mates when their own mate was fertile, and they had a lower success in achieving extra-pair fertilizations. Furthermore, UVR males tended to guard their mates more closely and lose more paternity in their own brood than C males did. We conclude that the treatment affected both social and extra-pair mate choice. This is the first experimental evidence that UV signalling influences male mating success in free-ranging birds.     

Reflectance spectra and mating patterns support intraspecific mimicry in the colour polymorphic damselfly <Emphasis Type="Italic">Ischnura elegans</Emphasis>

Coexistence of female colour morphs in animal populations is often considered the result of sexual conflict, where polymorphic females benefit from reduced male sexual harassment. Mate-searching males easily detect suitable partners when only one type of female is present, but become challenged when multiple female morphs coexist, which may result in frequency-dependent mate preferences. Intriguingly, in damselflies, one female morph often closely resembles the conspecific male in body coloration, which has lead to hypotheses regarding intra-specific male-mimicry. However, few studies have quantitatively evaluated the correspondence between colour reflectance spectra from males and male-like females, relying instead on qualitative visual assessments of coloration. Using colour analyses of reflectance spectra, we compared characteristics of the body coloration of ontogenetic male and female colour morphs of the damselfly Ischnura elegans. In addition, we evaluated whether males appear to (1) discriminate between immature and mature female colour morphs, and (2) whether male-like females experience reduced male mating attention and low mating frequencies as predicted from male-mimicry. Spectral reflectance data show that immature female morphs differ substantially in coloration from mature individuals. Mating frequencies were much lower for immature than mature female morphs. For the male-like female morph, measures of colour were statistically indistinguishable from that of both immature and mature conspecific males. Mating frequencies of male-like females were lower than those of other mature female morphs under field and experimental conditions. Together, our results indicate that males may use the observed spectral differences in mate choice decisions. Furthermore, male-like females may be regarded as functional mimics that have reduced attractiveness and lowered rates of sexual harassment by mate-searching males.     

Ultraviolet sexual dimorphism and assortative mating in blue tits

In spite of strong evidence for viability-based sexual selection and sex ratio adjustments, the blue tit, Parus caeruleus, is regarded as nearly sexually monomorphic and no epigamic signals have been found. The plumage coloration has not, however, been studied in relation to bird vision, which extends to the UV-A waveband (320 to 400 nm). Using molecular sex determination and UV/VIS spectrometry, we report here that blue tits are sexually dichromatic in UV/blue spectral purity (chroma) of the brilliant crown patch. It is displayed in courtship by horizontal posturing and erected nape feathers. A previously undescribed sexual dimorphism in crown size (controlling for body size) further supports its role as an epigamic ornament. Against grey-brown leaf litter and bark during pair formation in early spring, but also against green vegetation, UV contributes strongly to conspicuousness and sexual dimorphism. This should be further enhanced by the UV/bluish early morning skylight (''woodland shade'') in which blue tits display. Among 18 breeding pairs, there was strong assortative mating with respect to UV chroma, but not size, of the crown ornament. We conclude that blue tits are markedly sex dimorphic in their own visual world, and that UV/violet coloration probably plays a role in blue tit mate acquisition.     

Mutual Mate Choice for Colorful Traits in King Penguins

While studies of mate choice based on male color pattern are ubiquitous, studies of mate choice based on ornamental color traits in sexually monomorphic species are less common. We conducted manipulative field experiments on two color ornaments of king penguins (Aptenodytes patagonicus), the size of auricular patches of orange feathers and degree of UV reflectance from beak spots, to determine how the degree of ornamentation influenced pairing rate. In a reduction of auricular patch size, females paired significantly more quickly than males in both control and experimental samples. When this bias was taken into account statistically, pairing of individuals with reduced auricular patches was significantly delayed. We also reduced, but did not eliminate, UV reflectance from beak spots by applying a UV filter; no sex difference in pairing rate was evident in this experiment. Treated birds paired significantly more slowly than untreated control individuals, taking more than a week longer to pair on average than their unmanipulated counterparts, a result that was significant for males and approached significance for females. Our results may indicate mutual mate choice via UV reflectance of the beak spot. Given that this is a species where breeding is extremely slow and considerable investment by both males and females is required for successful reproduction, our results support the hypothesis that in such species, sexual selection might act on the same ornament in both sexes.     

Ultraviolet vision and mate choice in the guppy (Poecilia reticulata)

Ultraviolet (UV) vision is well documented for many speciesof vertebrates. UV cues are known to be used in foraging, navigationand in mate choice. We conducted a series of behavioral experimentsto investigate the role of UV perception in mate choice inboth female and male guppies (Poecilia reticulata). In ourexperiments the visual appearance of potential mates was manipulatedusing either UV transmitting (UV+) or UV blocking (UV-) filters.Female guppies significantly preferred UV+ males. Male guppiestended to prefer UV- females, but their preferences were marginallynonsignificant. Further experiments investigating the roleof luminance, indicate that UV wavelengths are probably beingused for color discrimination rather than for detecting differencesin brightness. These experiments raise the possibility thatUV is used in mate assessment in different ways by male andfemale guppies. This may reflect the different strategies thatthe two sexes have in order to maximize reproductive success.To our knowledge, these are the first data showing that UVis used by any fish species in mate selection.     

On the function of female ornaments: male bluethroats prefer colourful females

Female ornaments in animals with conventional sex roles have traditionally been considered non-functional, being merely a genetically correlated response to selection for male ornamentation. Alternatively, female ornaments may be influenced by selection acting directly on the females, either through female–female competition or male choice. We tested the latter hypothesis in mate choice experiments with bluethroats (Luscinia s. svecica), a passerine bird in which females vary considerably in coloration of an ornamental throat patch. In outdoor aviaries placed in prime breeding habitat, males were allowed to choose between a colourful and a drab female. We found that males associated more with, and performed more sexual behaviours towards, colourful females. Female coloration was not age-related, but correlated significantly with body mass and tarsus length. Thus, we have demonstrated both a male preference for female ornamentation, and a relationship between ornament expression and female body size, which may be indicative of quality. Our results refute the correlated response hypothesis and support the hypothesis that female ornamentation is sexually selected.     

Carotenoid-based bill colour as an indicator of immunocompetence and sperm performance in male mallards

Female mate choice is often based on exaggerated sexual traits, signals of male qualities that females cannot assess directly. Two such key qualities are male immune and/or sexual competence, whereby honesty in signalling could be maintained by physiological trade-offs. Carotenoid-based ornaments likely constitute such honest signals, as there is direct competition for (limited) carotenoids between ornament deposition and anti-oxidant support of immune or sperm functioning. Using spectrometry, we assessed the potential signalling function of the yellow, carotenoid-based colour of the bill of male mallards, a target of female mate choice. Here we demonstrate that bill reflectance varied with plasma carotenoid level, indicating antioxidant reserves. Moreover, lower relative UV reflectance during autumn pairing predicted immune responsiveness and correlated positively with sperm velocity during breeding, a trait that affects fertility. Our data provide support for current theories that females could use carotenoid-based sexual signals to detect immune vigour and fertilizing ability of prospective mates.     

I'm sexy and I glow it: female ornamentation in a nocturnal capital breeder

In many species, males rely on sexual ornaments to attract females. Females, by contrast, rarely produce ornaments. The glow-worm (Lampyris noctiluca) is an exception where wingless females glow to attract males that fly in search of females. However, little is known about the factors that promote the evolution of female ornaments in a sexual selection context. Here, we investigated if the female ornament of the glow-worm is a signal of fecundity used in male mate choice. In support of this, we found brightness to correlate with female fecundity, and males to prefer brighter dummy females. Thus, the glow emitted by females is a reliable sexual signal of female fecundity. It is likely that male preference for the fecundity-indicating ornament has evolved because of large variation among females in fecundity, and because nocturnal males cannot directly assess female size and fecundity. These results indicate that female ornamentation may evolve in capital breeders (i.e. those in which stored resources are invested in reproduction) when females vary significantly in fecundity and this variation cannot be assessed directly by males.     

Tail colour signals performance in blue tit nestlings

Indirect sexual selection arises when reproductive individuals choose their mates based on heritable ornaments that are genetically correlated to fitness. Evidence for genetic associations between ornamental colouration and fitness remains scarce. In this study, we investigate the quantitative genetic relationship between different aspects of tail structural colouration (brightness, hue and UV chroma) and performance (cell‐mediated immunity, body mass and wing length) in blue tit (Cyanistes caeruleus) nestlings. In line with previous studies, we find low heritability for structural colouration and moderate heritability for performance measures. Multivariate animal models show positive genetic correlations between the three measures of performance, indicating quantitative genetic variation for overall performance, and tail brightness and UV chroma, two genetically independent colour measures, are genetically correlated with performance (positively and negatively, respectively). Our results suggest that mate choice based on independent aspects of tail colouration can have fitness payoffs in blue tits and provide support for the indirect benefits hypothesis. However, low heritability of tail structural colouration implies that indirect sexual selection on mate choice for this ornament will be a weak evolutionary force.     

Ultraviolet reflection and female mate choice in the pied flycatcher, Ficedula hypoleuca

In pied flycatchers females seem to prefer male territory quality rather than male characteristics, and the results of female mate choice experiments are divergent. In this outdoor aviary study, we examined how altering the ultraviolet reflection of males affects female mate choice behaviour. We chose pairs of males with similar human-visible dorsal colour and morphological traits. We then reduced the proportional ultraviolet reflectance in one male with sunscreen chemicals. The other male was treated with a chemical that slightly increased the ultraviolet reflectance of the plumage. In the experiment females clearly preferred males with slightly increased ultraviolet reflection. Our results indicate that pied flycatcher females use ultraviolet cues for mate choice when the effect of territory quality is controlled for. The results give us new information about a possible mechanism of mate assessment in this species, and indicate the importance of colour cues in avian mate choice behaviour.     

Response to color by male and female Frankliniella occidentalis during swarming and non-swarming behavior

Responses of male and female Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) to colors of various hues and brightness levels were compared between swarming and non-swarming behavior periods. Relative rankings of color preference were similar between males and females and between swarming and non-swarming behavior periods. Numbers of thrips were higher on blues, violets, white and somewhat less on some yellows, while lower numbers were found on greens, reds, some yellows and highly UV reflective white. The effect of UV reflection on thrips response to color depended upon the amount of UV reflectance. Highly UV reflective white (78% reflectance at 365 nm) captured very few thrips compared with low UV white (14% reflectance at 365 nm), but colors with less than 35% UV reflectance had no negative effect on numbers of thrips captured compared with their lower UV counterparts. Correlations of average preference rank of colors across all tests with relative rank of brightness of the colors (based on the area under the reflectance curve in different spectral ranges) indicated highly significant correlations of preference with the brightness in the blue-violet range (R=0.69 for females; R=0.86 for males, P<0.0021), but no significant correlation with brightness in the visible, green-yellow, or UV range. This contrasts with previous physiological research which indicates that spectral response efficiency of this species peaks in the UV and at 540 nm (green-yellow range). Several possible physiological, behavioral and color brightness explanations for this discrepancy are discussed.Significantly higher numbers of male thrips were trapped during swarming (4.5–6.3×) compared with non-swarming behavior periods. Significantly higher numbers of males were trapped than females during swarming behavior periods, but more females were trapped than males during non-swarming behavior periods. Sex ratios during non-swarming periods approximated sex ratios found in populations in plants. Based on the density change relative to sex ratio change between behavior periods, there was an indication of a greater change in male behavior than in female behavior. Since males and females responded similarly to color during both behavior periods and attractive colors were similar to flower colors, this suggests that male thrips use resource-based areas for aggregation sites.     

The Role of Wing Pigmentation, UV and Fluorescence as Signals in a Neotropical Damselfly

Pigmentation patterns, ultraviolet reflection and fluorescent emission are often involved in mate recognition and mate quality functions in many animal taxa. We investigated the role of wing ultra-violet reflection, fluorescence emission, and pigmentation on age and sexual signals in the damselfly Mnesarete pudica. In this species, wings are sexually dimorphic in colour and exhibit age dependency: males and females show a smoky black colouration when young, turning red in mature males while it turns brown in females. First, we investigated wing UV patterns through reflectance and emission spectra. Second, behavioural experiments were undertaken to show male and female responses to manipulated wing pigmentation and experimentally reduced UV (UV-). Reflectance spectra of the wings of juvenile and mature males and females were used to show the differences between controls and individuals with manipulated colouration used in the behavioural experiment. UV-reduced, females with wings painted red, and control males and females were tethered and presented to conspecific males and females, and their behavioral responses were recorded. The male red wing pigmentation and females with red wings elicited an aggressive response in territorial males and a sexual response in females. Both males and females showed neutral responses towards individuals with reduced UV. Wing signals of juvenile individuals also provoked neutral responses. These results suggest that UV, together with pigmentation, plays a role during mate recognition in males and females. Other than butterflies and spiders, it seems that fluorescence signals and UV reflectance can also be part of communication in odonates.     

Ultraviolet vision, fluorescence and mate choice in a parrot, the budgerigar Melopsittacus undulatus.

As in many parrots, the plumage of the budgerigar Melopsittacus undulatus reflects near-ultraviolet (UVA) wavelengths (300-400 nm) and exhibits UVA-induced fluorescence. However, there have, to our knowledge, been no tests of whether the yellow fluorescence observed under intense UVA illumination has any role in signalling. Four experiments were carried out on wild-type budgerigars, where the presence and absence of UV reflectance and fluorescence were manipulated using filters. Few studies have attempted to separate the contribution of UV reflectance to plumage hue as opposed to brightness or distinguish between a role in sexual as opposed to social preferences. However, our first experiments show that not only do females consistently prefer UV-reflecting males, but also that the observed preferences are due to removal of UV affecting the perceived hue rather than brightness. Furthermore, we found no effect of the light environment on male response to females, suggesting that the female preferences relate to plumage colour per se. Whilst UV reflectance appears important in heterosexual choice by females, it has no detectable influence on same-sex association preferences. The results from the second series of experiments suggest that enhancement of the budgerigar's yellow coloration through fluorescence has no effect on male attractiveness. However, the fluorescent plumage may play a role in signalling by virtue of the fact that it absorbs UVA and so increases contrast with nearby UV-reflecting plumage. Our study provides convincing evidence that UV reflectances can play a role in mate choice in non-passerines, but no evidence that the yellow fluorescence observed under UVA illumination is itself important as a signal.     

Ultraviolet Ornamentation and Male Mating Success in a High-Density Assemblage of the Butterfly Colias eurytheme

Ultraviolet (UV) colour patterns, particularly those deriving from surface structures, serve a role in sexual signalling and mate choice in a range of animal groups. In the butterfly Colias eurytheme (Pieridae), male-limited iridescent UV functions in species recognition, and has potential as an intraspecific sexual signal of mate quality. I compared the dorsal colouration and body size of males discovered ‘in-copula’ (N = 95) with a random sample of free-flying individuals (N = 129), both collected from a high density agricultural population located in Chandler, U.S.A. Despite reasonable variance in each trait, I found no among-group differences in UV characters (brightness, hue and angular visibility) or in the coincident pigmentary yellowish-orange (brightness and saturation). Statistical power was sufficient to detect all but the smallest among-group differences, and there was a marginally significant tendency for in-copula males to be larger. These data do not support the hypothesis for intraspecific female choice upon male dorsal colouration. However, I discuss how the density and apparently very young age of individuals in the sampling population may have pre-disposed this result, and thus, how sexual selection on male colouration may operate in a density dependent manner.     

Condition dependence of iridescent wing flash-marks in two species of dabbling ducks

Growing empirical evidence supports the hypothesis of male mate choice for female ornaments which are thought to reflect individual quality and future breeding ability. While structural colors are clearly used in mate choice and pairing, the condition dependence of such traits is less obvious, particularly in females. We present spectral measurements of wing flash-marks in two species of dabbling ducks during the pairing period and evaluate color and brightness contrasts as seen through the mallard's (Anas platyrhynchos) visual system. We tested for possible relationships between body size (and condition) and feather measurements both on captive and wild individuals. By analyzing reflectance spectra of semi-captive mallards soon after the molting period, we found that brightness was condition related. Color contrast was positively related to body size, but only in females. In wild ducks, color contrast was positively related to body size in the common teal A. crecca only for females. These results suggest that female color traits are likely to be used by males for mate choice, and support the hypothesis that the structural color is condition-dependent. Finally, brightness contrast decreased over time in both duck species. Natural abrasion or the effect of keratinolytic bacteria could explain such pattern.