The Experts below are selected from a list of 73725 Experts worldwide ranked by ideXlab platform
Juan J. Soler - One of the best experts on this subject based on the ideXlab platform.
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Beak colour reflects circulating carotenoid and vitamin A levels in spotless starlings (Sturnus unicolor)
Behavioral Ecology and Sociobiology, 2010Co-Authors: Carlos Navarro, Tomás Pérez-contreras, Jesús M. Avilés, Kevin J. Mcgraw, Juan J. SolerAbstract:Many colourful sexually selected signals in animals are carotenoid-dependent and, because carotenoids function as antiradicals and immunostimulating molecules, carotenoid-dependent signals may honestly reflect the health state of individuals. Some others nutrients like vitamin A may also enhance health and Colouration, but these have rarely been tested alongside carotenoids in colourful birds. Here, we examined whether beak colour of the spotless starling ( Sturnus unicolor ) reflected circulating levels of carotenoids and/or vitamin A (retinol). Spotless starlings are polygynous, sexually dimorphic birds (i.e. length of chest feathers). The tip of the beaks of male and female spotless starlings is more intensely coloured at the beginning of the breeding season and becomes dull after mating, which may suggest a sexual function. We found that females have a more intensely coloured beak and higher plasma carotenoid concentration than males during mating, and, despite the finding that carotenoid and vitamin A levels were not significantly related; colour intensity was positively correlated with plasma concentration of carotenoids and vitamin A in both sexes. However, adult beak coloration was not associated with carotenoid and vitamin A concentrations after nestlings were hatched. Therefore, beak Colouration of spotless starlings provides information about circulating levels of carotenoids and vitamins during the mating season and may potentially function as a reliable signal of physiological status in the context of sexual selection.
Geoffrey E. Hill - One of the best experts on this subject based on the ideXlab platform.
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an experimental test of the role of structural blue and melanin based chestnut coloration in aggressive contests in male eastern bluebirds
Frontiers in Ecology and Evolution, 2014Co-Authors: Austi Mercadante, Geoffrey E. HillAbstract:Male eastern bluebirds (Sialia sialis) have feathers with either structurally based blue coloration or melanin-based chestnut coloration, and they hold territories during the breeding season that they defend vigorously. We tested whether the melanin pigmentation or structural coloration of feathers serve as signals during intrasexual aggressive encounters by placing color-modified stuffed bluebirds in male territories. We recorded the time to attack and the intensity of attacks on each model, and we then compared the response to color-enhanced versus color-reduced models. Male bluebirds attacked models with brighter and more chromatic blue coloration significantly more often than they attacked models with darker and less chromatic blue coloration. In contrast, the darkness of the chestnut breast coloration did not have a significant effect on the rate at which models were attacked. We conclude that territorial male bluebirds perceive intruding males with brighter blue coloration as a greater threat than males with drabber blue coloration, presumably because blue coloration is a signal of fighting ability. In contrast, the chestnut coloration of breast feathers appears to be a signal of gender and sexual maturity and not a graded signal of social status.
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A field test of female mate preference for male plumage coloration in eastern bluebirds
Animal behaviour, 2009Co-Authors: Mark Liu, Lynn Siefferman, Herman L. Mays, John E. Steffen, Geoffrey E. HillAbstract:A growing body of evidence shows that female birds use male plumage coloration as an important criterion in mate choice. In the field, however, males with brighter coloration may both compete better for high quality territories and be the object of female choice. Positive associations between territory quality, male-male competitive ability, and female preferences can make it difficult to determine whether females actively choose the most ornamented males. Male eastern bluebirds (Sialia sialis) display brilliant ultraviolet (UV)-blue plumage coloration on their heads, backs, wings, and tails, and chestnut coloration on their breasts which is positively correlated with condition, reproductive effort, and reproductive success. We tested the hypothesis that female bluebirds prefer males that display brighter and more chromatic coloration by widowing males in the field and allowing replacement females to choose partners. We controlled for the influence of territory quality on female choice by widowing dyads of males with adjacent territories. We found no evidence that UV-blue or chestnut plumage coloration, body size, or body condition predicted the male with which females would pair. We found no support for the hypothesis that the coloration of male eastern bluebirds functions as a criterion in female mate choice.
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An experimental test of female choice relative to male structural coloration in eastern bluebirds
Behavioral Ecology and Sociobiology, 2006Co-Authors: Mark Liu, Lynn Siefferman, Geoffrey E. HillAbstract:Several experimental studies have shown that female birds use ornamental melanin and carotenoid plumage coloration as criteria in mate choice. Whether females choose mates based on natural variation in structural coloration, however, has not been well established. Male eastern bluebirds (Sialia sialis) display brilliant ultraviolet (UV)-blue plumage coloration on their head, back, wings, and tail, which is positively correlated with condition, reproductive effort, and reproductive success. We experimentally tested the hypothesis that female eastern bluebirds prefer as mates males that display brighter structural coloration by presenting breeding-condition females with males of variable coloration. We conducted two types of mate-choice experiments. First, females chose between males whose coloration was manipulated within the natural range of variation in the population; feathers were either brightened with violet marker or dulled with black marker. Second, females chose between males with naturally dull or bright plumage coloration. In both manipulated and unmanipulated coloration trials, female choice did not differ significantly from random with respect to structural coloration. We found no support for the hypothesis that the UV–blue coloration of male eastern bluebirds functions as a criterion in female mate choice.
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Blue structural coloration of male eastern bluebirds Sialia sialis predicts incubation provisioning to females
Journal of Avian Biology, 2005Co-Authors: Lynn Siefferman, Geoffrey E. HillAbstract:Plumage coloration has been suggested to serve as an honest signal of benefits that males provide to females. One benefit proposed for females that choose to mate with elaborately colored males is that such males might provide more food resources to the females. To test this hypothesis, we investigated the relationship between the rates at which males provisioned incubating females and the structural ultraviolet (UV)/blue coloration and melanin-based chestnut coloration of male eastern bluebirds Sialia sialis, a sexually dichromatic songbird in which coloration has been shown to be sexually selected in males. We found that males with brighter UV/blue coloration provisioned incubating females more often than did drabber males. Melanin coloration, however, was not correlated with provisioning rates. Moreover, provisioning rates were correlated with the length of time that females spent off the nest, indicating an important benefit of increased male provisioning. These data support the hypothesis that female bluebirds receive direct resource benefits by pairing with males with bright structural coloration.
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Evidence for sexual selection on structural plumage coloration in female eastern bluebirds (Sialia sialis).
Evolution, 2005Co-Authors: Lynn Siefferman, Geoffrey E. HillAbstract:Although the function of ornamental traits in males has been the focus of intensive research for decades, expression of such traits in females has received much less study. Eastern bluebirds (Sialia sialis) display structurally based ultraviolet/blue and melanin-based chestnut plumage, and in males this plumage coloration is related to both reproductive success and competitive ability. Compared to males, female bluebirds show a subdued expression of blue and chestnut ornamental coloration, and we used a combination of an aviary nutritional-stress experiment and four years of field data to test the hypothesis that coloration functions as a signal of female quality. First, we tested the effect of food intake on expression of structural and melanin coloration in female eastern bluebirds to determine whether structural or melanin coloration are condition-dependent traits. Females that were given ad libitum access to food displayed more ornamented structural coloration than females on a food-restricted diet, but there was no effect of the experiment on melanin ornamentation. Second, we used field data to assess whether female ornamentation correlated with measures of mate quality and parental effort. The structural coloration of females predicted first egg date, maternal provisioning rates, and measures of reproductive success. These data indicate that structural coloration is dependent on nutritional condition and suggest that sexual selection is acting on structurally based plumage coloration in female eastern bluebirds.
Ivan Miksik - One of the best experts on this subject based on the ideXlab platform.
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Egg pigmentation reflects female and egg quality in the spotless starling Sturnus unicolor
Behavioral Ecology and Sociobiology, 2008Co-Authors: Isabel López-rull, Ivan MiksikAbstract:It has been proposed that blue Colouration in eggs has evolved as a signal of female quality that males can use to modulate their parental investment. This hypothesis is based in the antioxidant properties of biliverdin whose costly deposition in the eggshell is expected to signal female antioxidant capacity and egg quality. Since maternally derived androgens are costly to produce and may adaptively affect offspring phenotype, high-quality females may benefit by signalling their androgen investment through egg Colouration. Our aim was to investigate whether egg colour variation in the spotless starling reflected the amount of pigments on the eggshell and whether egg pigmentation was related to female and egg quality. Chromatography analyses revealed that spotless starling eggshells contained two different pigments: biliverdin and protoporphyrin IX with no correlation between them. Biliverdin contents correlated positively with egg Colouration indicating that darker eggs with a higher peak in the blue–green segment of the spectrum contained higher amounts of biliverdin. Eggs containing more biliverdin were laid by high-quality females and contained higher yolk testosterone levels. However, despite the strong correlation between biliverdin and colorimetric variables, egg Colouration did not reflect accurately female and egg quality. Our results provide evidence that eggshell pigmentation in the spotless starling is related to female and egg quality as shown by the yolk testosterone levels. However, the lack of relation between egg colour and female condition and egg quality do not provide evidence to support the signalling function of egg Colouration.
Carlos Navarro - One of the best experts on this subject based on the ideXlab platform.
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Beak colour reflects circulating carotenoid and vitamin A levels in spotless starlings (Sturnus unicolor)
Behavioral Ecology and Sociobiology, 2010Co-Authors: Carlos Navarro, Tomás Pérez-contreras, Jesús M. Avilés, Kevin J. Mcgraw, Juan J. SolerAbstract:Many colourful sexually selected signals in animals are carotenoid-dependent and, because carotenoids function as antiradicals and immunostimulating molecules, carotenoid-dependent signals may honestly reflect the health state of individuals. Some others nutrients like vitamin A may also enhance health and Colouration, but these have rarely been tested alongside carotenoids in colourful birds. Here, we examined whether beak colour of the spotless starling ( Sturnus unicolor ) reflected circulating levels of carotenoids and/or vitamin A (retinol). Spotless starlings are polygynous, sexually dimorphic birds (i.e. length of chest feathers). The tip of the beaks of male and female spotless starlings is more intensely coloured at the beginning of the breeding season and becomes dull after mating, which may suggest a sexual function. We found that females have a more intensely coloured beak and higher plasma carotenoid concentration than males during mating, and, despite the finding that carotenoid and vitamin A levels were not significantly related; colour intensity was positively correlated with plasma concentration of carotenoids and vitamin A in both sexes. However, adult beak coloration was not associated with carotenoid and vitamin A concentrations after nestlings were hatched. Therefore, beak Colouration of spotless starlings provides information about circulating levels of carotenoids and vitamins during the mating season and may potentially function as a reliable signal of physiological status in the context of sexual selection.
Isabel López-rull - One of the best experts on this subject based on the ideXlab platform.
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Egg pigmentation reflects female and egg quality in the spotless starling Sturnus unicolor
Behavioral Ecology and Sociobiology, 2008Co-Authors: Isabel López-rull, Ivan MiksikAbstract:It has been proposed that blue Colouration in eggs has evolved as a signal of female quality that males can use to modulate their parental investment. This hypothesis is based in the antioxidant properties of biliverdin whose costly deposition in the eggshell is expected to signal female antioxidant capacity and egg quality. Since maternally derived androgens are costly to produce and may adaptively affect offspring phenotype, high-quality females may benefit by signalling their androgen investment through egg Colouration. Our aim was to investigate whether egg colour variation in the spotless starling reflected the amount of pigments on the eggshell and whether egg pigmentation was related to female and egg quality. Chromatography analyses revealed that spotless starling eggshells contained two different pigments: biliverdin and protoporphyrin IX with no correlation between them. Biliverdin contents correlated positively with egg Colouration indicating that darker eggs with a higher peak in the blue–green segment of the spectrum contained higher amounts of biliverdin. Eggs containing more biliverdin were laid by high-quality females and contained higher yolk testosterone levels. However, despite the strong correlation between biliverdin and colorimetric variables, egg Colouration did not reflect accurately female and egg quality. Our results provide evidence that eggshell pigmentation in the spotless starling is related to female and egg quality as shown by the yolk testosterone levels. However, the lack of relation between egg colour and female condition and egg quality do not provide evidence to support the signalling function of egg Colouration.
