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Colour Expression (colour + expression)
Selected AbstractsCarotenoid accumulation strategies for becoming a colourful House Finch: analyses of plasma and liver pigments in wild moulting birdsFUNCTIONAL ECOLOGY, Issue 4 2006K. J. MCGRAW Summary 1Male House Finches (Carpodacus mexicanus) colour their sexually selected plumage with carotenoid pigments, and there has been much interest in the factors that affect their ability to become bright red rather than drab yellow. 2There is good support for the notions that health, nutritional condition and total carotenoid intake influence colour expression, but there are also suggestions that acquiring particular types of carotenoids from the diet may be important for developing red plumage. 3We used high-performance liquid chromatography (HPLC) to analyse the types and amounts of endogenous (in plasma and liver) and integumentary (in newly grown feathers) carotenoids in a wild, native population of moulting male and female House Finches from the south-western United States to determine the carotenoid-accumulation strategies for becoming optimally colourful. 4Four plant carotenoids , lutein, zeaxanthin, ,-cryptoxanthin and ,-carotene , were detected in plasma and liver. However, as was found previously, 11 carotenoids were observed in colourful plumage, with xanthophylls (e.g. lutein, dehydrolutein) predominant in yellow feathers and ketocarotenoids (e.g. adonirubin, 3-hydroxy-echinenone) in red feathers. This indicates endogenous modification of ingested carotenoids. 5Birds that accumulated more of one type of carotenoid in plasma and liver did not necessarily accumulate more of all other types, suggesting that individuals are not employing a simple ,more is better' strategy for coloration. Instead, when forward stepwise regression was used to examine the ability of individual types of carotenoids in plasma and liver to explain variation in red plumage pigments and plumage redness, we found that the lone variable remaining in all models was ,-cryptoxanthin concentration. 6This supports the idea that, unlike some other songbirds (e.g. yellow Carduelis finches), there is a specialized biochemical strategy that male House Finches follow to become red and most sexually attractive , to accumulate as much ,-cryptoxanthin in the body as possible. ,-Cryptoxanthin is a less common dietary carotenoid than the typical xanthophylls and carotenes in grains and fruits and may be limited enough in the diet that, to become colourful, House Finches might adopt selective foraging strategies for the most ,-cryptoxanthin-rich foods. [source] Moult speed affects structural feather ornaments in the blue titJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 4 2009M. GRIGGIO Abstract Growing evidence suggests that structural feather colours honestly reflect individual quality or body condition but, contrary to pigment-based colours, it is not clear what mechanism links condition to reflectance in structural feather colours. We experimentally accelerated the moult speed of a group of blue tits (Cyanistes caeruleus) by exposing them to a rapidly decreasing photoperiod and compared the spectral characteristics of their structural feather colours with those of control birds. Blue tits were sexually dimorphic on the UV/blue crown and on the white cheek feathers. Moult speed, however, dramatically reduced brightness and the saturation only on the UV/blue crown feathers, whereas structural white on the cheek feathers was basically unaffected by moult speed. Given that the time available for moulting is usually confined to the period between the end of the breeding season and migration or wintering, UV/blue colours, but not structural white, may convey long-term information about an individual's performance during the previous breeding season. The trade-off between fast moulting and structural colour expression may represent a previously unrecognized selective advantage for early-breeding birds. [source] The oxidation handicap hypothesis and the carotenoid allocation trade-offJOURNAL OF EVOLUTIONARY BIOLOGY, Issue 6 2008C. ALONSO-ALVAREZ Abstract The oxidation handicap hypothesis proposes that testosterone mediates the trade-off between the expression of secondary sexual traits and the fight against free radicals. Coloured traits controlled by testosterone can be produced by carotenoid pigments (yellow,orange,red traits), but carotenoids also help to quench free radicals. Recently, it has been shown that testosterone increases the amount of circulating carotenoids in birds. Here, a testosterone-mediated trade-off in the carotenoid allocation between colour expression and the fight against oxidative stress is proposed. Male red-legged partridges were treated with testosterone, anti-androgens or manipulated as controls. Testosterone-treated males maintained the highest circulating carotenoid levels, but showed the palest red traits and no evidence of oxidative damage. Increased levels of a key intracellular antioxidant (i.e. glutathione) indicated that an oxidative challenge was in fact induced but controlled. The trade-off was apparently solved by reducing redness, allowing increased carotenoid availability, which could have contributed to buffer oxidative stress. [source] Proximate mechanisms of variation in the carotenoid-based plumage coloration of nestling great tits (Parus major L.)JOURNAL OF EVOLUTIONARY BIOLOGY, Issue 1 2003B. Tschirren Abstract Many vertebrates use carotenoid-based signals in social or sexual interactions. Honest signalling via carotenoids implies some limitation of carotenoid-based colour expression among phenotypes in the wild, and at least five limiting proximate mechanisms have been hypothesized. Limitation may arise by carotenoid-availability, genetic constraints, body condition, parasites, or detrimental effects of carotenoids. An understanding of the relative importance of the five mechanisms is relevant in the context of natural and sexual selection acting on signal evolution. In an experimental field study with carotenoid supplementation, simultaneous cross-fostering, manipulation of brood size and ectoparasite load, we investigated the relative importance of these mechanisms for the variation in carotenoid-based coloration of nestling great tits (Parus major). Carotenoid-based plumage coloration was significantly related to genetic origin of nestlings, and was enhanced both in carotenoid-supplemented nestlings, and nestlings raised in reduced broods. We found a tendency for ectoparasite-induced limitation of colour expression and no evidence for detrimental effects of carotenoids on growth pattern, mortality and recruitment of nestlings to the local breeding population. Thus, three of the five proposed mechanisms can generate individual variation in the expression of carotenoid-based plumage coloration in the wild and thus could maintain honesty in a trait potentially used for signalling of individual quality. [source] Effects of genetics and light environment on colour expression in threespine sticklebacksBIOLOGICAL JOURNAL OF THE LINNEAN SOCIETY, Issue 4 2008EVA LEWANDOWSKI The genetic basis of traits that are under sexual selection and that are involved in recognizing conspecific mates is poorly known, even in systems in which the phenotypic basis of these traits has been well studied. In the present study, we investigate genetic and environmental influences on nuptial colour, which plays important roles in sexual selection and sexual isolation in species pairs of limnetic and benthic threespine sticklebacks (Gasterosteus aculeatus species complex). Previous work demonstrated that colour differences among species correlate to differences in the ambient light prevalent in their mating habitat. Red fish are found in clear water and black fish in red-shifted habitats. We used a paternal half-sib split-clutch design to investigate the genetic and environmental basis of nuptial colour. We found genetic differences between a red and a black stickleback population in the expression of both red and black nuptial colour. In addition, the light environment influenced colour expression, and genotype by environment interactions were also present. We found evidence for both phenotypic and genetic correlations between our colour traits; some of these correlations are in opposite directions for our red and black populations. These results suggest that both genetic change and phenotypic plasticity underlie the correlation of male colour with light environment. © 2008 The Linnean Society of London, Biological Journal of the Linnean Society, 2008, 94, 663,673. [source] | ||||||||||