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A tremendous diversity of avian color displays has stimulated numerous studies of natural and sexual selection. Yet, the developmental mechanisms that produce such diversification, and thus the proximate targets of selection pressures, are rarely addressed and poorly understood. In particular, because feathers are colored during growth, the dynamics of feather growth play a deterministic role in the variation in ornamentation. No study to date, however, has addressed the contribution of feather growth to the expression of carotenoid-based ornamentation. Here, we examine the developmental basis of variation in ornamental feather shapes in male house finches (Carpodacus mexicanus)--a species in which carotenoid displays are under strong natural and sexual selection. First, we use geometric morphometrics to partition the observed shape variation in fully grown feathers among populations, ages, degrees of elaboration, ornamental body parts, and individuals. Second, we use a biologically informed mathematical model of feather growth to predict variation in shape of ornamental feathers due to simulated growth rate, angle of helical growth of feather barbs, initial number of barb ridges, rate of addition of new barbs, barb diameter, and ramus-expansion angle. We find close concordance between among-individual variation in feather shape and hue of entire ornament, and show that this concordance can be attributed to a shared mechanism--growth rate of feather barbs. Predicted differences in feather shape due to rate of addition of barbs and helical angle of feather growth explained observed variation in ornamental area both among individuals and between populations, whereas differences in helical angle of growth and the number of barbs in the feather follicle explained differences in feather shape between ornamental parts and among males of different ages. The findings of a close association of feather growth dynamics and overall ornamentation identify the proximate targets of selection for elaboration of sexual displays. Moreover, the close association of feather growth and pigmentation not only can reinforce condition-dependence in color displays, but can also enable phenotypic and genetic accommodation of novel pigments into plumage displays providing a mechanism for the observed concordance of within-population developmental processes and between-population diversification of color displays. [ABSTRACT FROM AUTHOR]

Asymmetry in bilateral traits is often used to assess an individual's quality and stress resistance, but stress-induced variation in developmental stability is largely undocumented for free-living populations. Over many years, grizzly bears (Ursus arctos horribilis) extensively foraged around garbage dumps in Yellowstone National Park. Abrupt closure of these dumps 26 years ago was a severely stressful event and was followed by excessive mortality and a many-fold increase in grizzly home-range size. I examine how this stress affected developmental stability by comparing dentition of bears born before and after the dump closure. I predicted that (1) asymmetry in dentition should be greater in bears born after dump closure compared to before closure, and asymmetry in sexually selected canines should change more than nonsexually selected premolars following dump closure and (2) the relationship between tooth asymmetry and tooth size should change in the populations following the stressful events as compared with populations before stressful events. I found that developmental stability of canines, which are under directional sexual selection in males, was more responsive to stress compared to that of male premolars or female dentition (both under stabilizing selection), and, because of the increased cost of canine production, fewer animals were able to achieve both large size and symmetrical development of these teeth, and thus the slope of the relationship between fluctuating asymmetry and canine size increased. I conclude that stress appears to act as an honesty-reinforcement mechanism in sexual selection for symmetrical dentition. [ABSTRACT FROM AUTHOR]

The colder climate and disjunct distribution of nesting and foraging habitats at high elevations increases the necessity of biparental care for successful breeding in birds. If differences in parental investment between the sexes correlate with intensity of sexual selection, the intensity of sexual selection should covary with ecological factors associated with elevation. I used sexual dimorphism as an indirect measure of intensity of sexual selection and examined variation in sexual dimorphism in 126 extant species of cardueline finches. I controlled for phylogeny and potential confounding factors and tested the prediction that the extent of sexual dimorphism negatively covaries with elevation of breeding. As predicted, interspecific variation in sexual dimorphism was more strongly associated with changes in elevation than with habitat, nest dispersion and placement, and migratory status. Species occupying lower elevations were more sexually dimorphic in plumage than species at higher elevations. This variation was largely due to increased brightness of male plumage at lower elevations. I address possible explanations of this trend, which may include increased opportunities for extrapair fertilizations at lower elevations, an increase in the cost of secondary sexual trait production (i.e., molt) and maintenance at high elevations, and elevational variation in predation pressure [ABSTRACT FROM AUTHOR]

Summary Tarsal spurs play an important role in intrasexual competition for females among male wild turkeys (Meleagris gallopavo ). Thus variation in spur development may have important fitness consequences. Fitness correlates of spur development were studied in a free-living population of wild turkeys and it was found that heavier males and males with longer beards had longer spurs. Males that had longer spurs spent more time on display areas during the breeding season and less time moving among these areas compared to males with shorter spurs, independently of their body mass. Otherwise ideally symmetrical spurs showed fluctuating asymmetry between left and right tarsi, the degree of absolute asymmetry decreased with spur length in adults, but not in subadults, and males that survived at least one winter had more symmetrical spurs compared to males that did not. We conclude that if the ability to produce symmetrical spurs has a genetic basis, then spur length and spur asymmetry could reliably indicate individual quality and that these traits are under directional selection for increased size and symmetry in wild turkeys. [ABSTRACT FROM AUTHOR]

The house finch ( Carpodacus mexicanus) has emerged recently as a model species in studies of sexual selection, reproductive physiology, population genetics, and epizootic disease ecology. Here we describe 17 highly polymorphic microsatellite loci for this species. In a sample of 36 individuals, we observed an average of 16 alleles per locus and heterozygosity ranged from 0.61 to 0.97. One locus showed significant deviation from Hardy–Weinberg proportions, but no significant gametic disequilibrium was observed among any of the loci. Amplification by polymerase chain reaction was optimized under similar parameters across loci, thereby facilitating multiplexing and rapid multilocus genotyping. [ABSTRACT FROM AUTHOR]