Search

Urban environments create a unique suite of conditions, leading to changes in animal behavior, morphology, phenology, and physiology. Condition-dependent traits such as the carotenoid-based coloration offer a unique opportunity to assess the impacts of urbanization on organisms because they reflect the nutrition, health, or other resource-based attributes of their bearers and they play an essential role in intra and intersex interactions. To determine if and how the carotenoid-based coloration of male house finches (Haemorhous mexicanus) varies along a gradient of urbanization, we quantified the plumage coloration of more than 1000 individuals in urban, suburban, rural, and desert habitats over the course of 17 months. We also examined for the first time the preference of females for male plumage coloration across the urban–rural gradient, to test if and how female preferences varied relative to the plumage coloration displayed by males in their local population. We found that carotenoid-based coloration decreased along the gradient of urbanization, suggesting that the enzyme-driven metabolic conversion of dietary carotenoids into red carotenoids used to color plumage is sensitive to urban stressors. The stronger negative effect of urbanization on carotenoid-based plumage coloration during breeding than during molt and winter suggests that urbanization affects color fading rate, maybe through modifications of feather-degrading bacterial load. Finally, we have shown that urbanization influences female mate-choice behavior, suggesting that female color preferences may track the variation in male coloration across the gradient of urbanization. [ABSTRACT FROM AUTHOR]

Ornamentation is hypothesized to signal the capacity of an individual to cope with environmental challenges. At the molecular level, organisms respond to their environments largely by altering gene transcription, but the transcriptional responses linking ornamentation and disease resistance are virtually unstudied. In the house finch (Haemorhous mexicanus), carotenoid coloration displayed by males is important in female choice, and plumage redness predicts a male's ability to recover from bacterial infection with Mycoplasma gallisepticum. To investigate the molecular mechanisms underlying links between ornamentation and disease response, we experimentally infected wild finches and used microarrays to identify genes that were differentially expressed in males with redder and yellower plumage coloration. Sixteen candidate genes were then investigated across individuals. Principal components analysis revealed that infection induced a marginally significant decrease in 11 genes, several with primary immune functions. The treatment by plumage color interaction effect was largely driven by greater disease-induced changes in expression of heat shock protein 90 and ubiquitin c (the second principal component) by red birds than by yellow birds. In a direct comparison of disease severity between infected birds, plumage color on its own did not significantly predict disease symptoms. However, in multivariate models, expression of genes loading on the second principal component, plumage color, and their interaction were significant predictors of the severity of disease symptoms. Our observations demonstrate links between ornamentation and expression of genes related to disease resistance; we suggest that male plumage color may reflect functionally associated differences in inducibility or plasticity of gene expression in this species. [ABSTRACT FROM AUTHOR]

Plumage coloration plays an important role in visual communication by signaling aspects of individual quality. It has been proposed that the need for preserving plumage condition and hence signaling content may have promoted a novel signaling mechanism: cosmetic coloration. Here, we investigated whether preen waxes may act as cosmetics by affecting feathers' ornamental coloration in male house finches (Carpodacus mexicanus). We (1) blocked the access to uropygial gland of a group of males and compared their coloration with a control group and (2) applied preen wax extracted from live individuals to museum skins and measured color before and after wax application. We found that red feathers of control males were more colorful than those of experimental males and that applying waxes to museum skins' red feathers increased their color saturation. Our results provide evidence that preen waxes act as cosmetics by enhancing plumage ornamentation, thus revealing the existence of novel mechanisms operating in signaling coloration. Although preen waxes per se would not constitute a signal, selection for signal efficacy might favor individuals that are able to increase signal intensity beyond the optimum necessary for plumage maintenance. Our results support the hypothesis that preen waxes reinforce the honesty of signals, which may be particularly useful in a social context where interactions between individuals are mediated by the intensity of the signals. [ABSTRACT FROM PUBLISHER]

Elaboration of costly sexual traits can reduce investment in other aspects of reproduction, such as parental care or intrasexual competition, which may lead to the evolution of alternative mating tactics. In house finches (Carpodacus mexicanus), less elaborately ornamented (dull) males tend to dominate more elaborated (redder) males, but redder males pair earlier and invest more in parental care. This suggests that males may pursue alternative parental or competitive tactics, depending on the elaboration of their sexual trait. Elevation of testosterone, a hormone that is closely associated with condition in male house finches, influences dominance and sexual behaviors but is antagonistic to parental behaviors. We tested the hypothesis that the higher dominance status of dull males reflects an alternative testosterone-dependent mating tactic. First, we experimentally manipulated the testosterone levels of captive males and measured the effect on dominance rank, and second, we measured the association of testosterone elevation and plumage hue in free-living males. We found that, as predicted, testosterone elevation increased dominance rank in captive males. However, in free-living males, testosterone levels were higher in redder males, suggesting that testosterone is dissociated from dominance status under natural circumstances. This may be because the context of social interactions and the higher motivation of dull males to access food resources have a stronger influence on the outcome of dominance interactions than does the physiological effects of testosterone elevation. In turn, the strong positive correlation between testosterone levels and plumage elaboration likely reflects the common condition dependence of these traits. [ABSTRACT FROM AUTHOR]

When individuals in a population differ in physiological condition and residual reproductive value, selection should favor phenotypic plasticity in reproductive investment such that individuals are able to adopt the reproductive tactic that results in the highest fitness under given conditions. Here we examined reproductive tactics in relation to the elaboration of condition-dependent sexual ornamentation (carotenoid breast coloration) in a Montana population of the house finches (Carpodacus mexicanus). Males used distinct reproductive tactics depending on elaboration of their sexual ornamentation. Males with red pigmentation (maximum ornament elaboration) paired with females that nested earlier, but these males did little provisioning of incubating females and nestlings. In contrast, males with yellow coloration paired with females that nested later, but these males fed female and nestlings more. Consequently, for red males offspring recruitment was primarily affected by earlier nest initiation, whereas in yellow males it was affected most by male provisioning. In males with intermediate plumage coloration, all measured components, nest initiation, provisioning of incubating female, and nestling feeding, strongly contributed to offspring recruitment. The fitness consequences of alternative reproductive tactics of males were influenced by breeding experience and fidelity of their mates. Among first-time breeders, red males achieved the highest fecundity because of the advantage gained through early nesting and pairing with more experienced females and because of compensation by their mates for low male provisioning of nestlings. Among experienced breeders, males with intermediate plumage coloration achieved the highest fecundity because of the combined benefits of relatively early pairing and high parental care. High variation in sexual ornamentation in a Montana population of house finches may favor distinct associations of sexual displays with a particular set of reproductive behaviors. [ABSTRACT FROM AUTHOR]

The status signaling hypothesis (SSH) was devised primarily to explain the adaptive significance of avian ornamental coloration during the nonbreeding season. It proposes that conspicuous male plumage serves as an honest signal of social status within a population of birds. However, to date this hypothesis has been well tested and supported for only one type of plumage coloration, melanin-based coloration. Carotenoid-based pigmentation is known to positively reveal male health and condition during molt in a variety of species, but it is poorly understood whether this ornament type can also function as a status signal during the winter. We tested the SSH in male house finches (Carpodacus mexicanus) by manipulating the carotenoid-based plumage brightness of first-year males and then pairing unfamiliar birds of differing coloration in a series of dominance trials in captivity. Manipulated plumage color was unrelated to win/loss outcome in these trials. Similarly, the natural pigmentation of males was a poor predictor of winter dominance; as in other studies with this species, we found only a weak tendency for naturally drab males to dominate naturally bright males. These results suggest that carotenoid-based coloration is not a reliable indicator of social status in male house finches during the nonbreeding season. In fact, carotenoid-based coloration may function only in mate choice in this species, and it may be retained throughout the year either because time constraints preclude a second plumage molt or because it aids in pair formation that begins in late winter. [ABSTRACT FROM AUTHOR]