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1.
Lifjeld JT Kleven O Jacobsen F McGraw KJ Safran RJ Robertson RJ 《Behavioral ecology and sociobiology》2011,65(9):1687-1697
When males become more ornamented and reproduce more successfully as they grow older, phenotypic correlations between ornament
exaggeration and reproductive success can be confounded with age effects in cross-sectional studies, and thus say relatively
little about sexual selection on these traits. This is exemplified here in a correlative study of male fertilization success
in a large colony of American barn swallows (Hirundo rustica erythrogaster). Previous studies of this species have indicated that two sexually dimorphic traits, tail length and ventral plumage coloration,
are positively correlated with male fertilization success, and a mechanism of sexual selection by female choice has been invoked.
However, these studies did not control for potential age-related variation in trait expression. Here, we show that male fertilization
success was positively correlated with male tail length but not with plumage coloration. We also show that 1-year-old males
had shorter tails and lower fertilization success than older males. This age effect accounted for much of the covariance between
tail length and fertilization success. Still, there was a positive relationship between tail length and fertilization success
among older males. But as this group consisted of males from different age classes, an age effect may be hidden in this relationship
as well. Our data also revealed a longitudinal increase in both tail length and fertilization success for individual males.
We argue that age-dependent ornament expression and reproductive performance in males complicate inferences about female preferences
and sexual selection. 相似文献
2.
3.
Testosterone upregulates lipoprotein status to control sexual attractiveness in a colorful songbird 总被引:4,自引:0,他引:4
Kevin J. McGraw Stephanie M. Correa Elizabeth Adkins-Regan 《Behavioral ecology and sociobiology》2006,60(2):117-122
A salient feature of many secondary sexual characteristics in animals is that their expression is controlled by sex-steroid hormones. However, for only a few types of ornaments do we know the precise molecular mechanism by which androgens like testosterone (T) enhance trait production. We studied the red carotenoid-based beak of male zebra finches (Taeniopygia guttata), which serves as a sexually selected trait and is thought to be T dependent. In previous research, we demonstrated that the extent to which male finches produce lipoproteins in the bloodstream, which bind carotenoid pigments acquired from the diet and transport them to peripheral tissues, regulates the accumulation of carotenoids in the body and beak pigmentation. Here we show that T acts to upregulate lipoprotein production and allows male zebra finches to display flashy, sexually attractive coloration. Levels of circulating T in blood positively and significantly predicted lipoprotein profile (as measured by cholesterol levels), blood carotenoid concentration, and beak color. Exogenous T administration elevated cholesterol and carotenoid status as well as beak redness. Last, experimental inhibition of T (using the anti-androgen flutamide) downregulated lipoprotein production and carotenoid circulation and faded the beak. This androgen- and lipoprotein-mediated system represents one of the more detailed physiological mechanisms underlying the development of a sex-steroid-dependent trait in animals. 相似文献
4.
Melissa G. Meadows Nathan I. Morehouse Ronald L. Rutowski Jonathan M. Douglas Kevin J. McGraw 《Behavioral ecology and sociobiology》2011,65(6):1317-1327
Quantification of animal colors is important to a variety of fields of research, especially those dealing with visual communication
and sexual selection. Most animal colors are easily measured using well-established spectrophotometric techniques. However,
the unique characteristics of iridescent colors present particular challenges and opportunities to quantify novel color metrics.
Due to the fine-scale angle dependence of iridescent coloration, color metrics, such as hue and brightness, must be measured
using methods that allow for repeatable comparison across individuals (e.g., by carefully controlling and measuring viewing
geometry). Here, we explain how the optical characteristics of iridescent colors should be considered when developing measurement
techniques, describe the pitfalls of some commonly used techniques, and recommend improved methods and metrics (angular degree
of color change and breadth of reflectance) for quantifying iridescent color. In particular, most studies of iridescent birds
to date have used less than ideal procedures and have not provided repeatability estimates for their methods. For example,
we demonstrate here that measuring coloration from overlapping patches of iridescent feathers may be problematic, and we argue
against methods that do not carefully control viewing geometry. We recommend measuring iridescence at maximal reflectance
angles using an apparatus that allows for sample rotation, and we compare this technique to some other commonly used methods
using iridescent gorget and crown feathers from Anna’s hummingbirds (Calypte anna). Our apparatus allows for the quantification of angular color change, and we found that maximal reflectance measurements
using single feathers are highly repeatable both within feather samples and among samples within an individual. 相似文献
5.
Michael W. Butler Matthew B. Toomey Kevin J. McGraw 《Behavioral ecology and sociobiology》2011,65(2):401-413
For a variety of technical and conceptual reasons, biologists have come to use several different methods to quantify the colors
of animals. However, the relative abilities of these different color-scoring procedures to capture variation in the actual
color-generating mechanisms—pigment or structural composition of the integument—have never been tested systematically. Here,
we examined which commonly employed color metrics predict carotenoid content of ornaments in three avian species (house finch
Carpodacus mexicanus, mallard duck Anas platyrhynchos, and zebra finch Taeniopygia guttata). We used spectrophotometry to measure reflectance spectra from beak and feather tissue, calculated numerous color metrics
(e.g., hue, chroma, brightness, principal components, and tetrahedral color space position) from these spectra, and determined
carotenoid content at the site of color measurement with high-performance liquid chromatography. We found that several principal
component, tristimulus, and avian visual model metrics significantly correlated with carotenoid content of house finch feathers
and duck beaks. Carotenoid content of mallard beaks was most closely correlated with brightness and saturation metrics, whereas
in house finch feathers, carotenoid concentration was best captured by hue and saturation metrics. According to tristimulus
scores and visual models, we found that the ultraviolet portion of the spectrum was not an essential predictor of variation
in carotenoid content. Also, visual model chromatic contrasts generally were not significant predictors of carotenoid content,
although some achromatic contrasts and tetrahedral color space vector parameters were. Our results indicate that numerous
methods, especially tristimulus scores, are suitable for capturing pigment-based color variation in two carotenoid-containing
ornaments, and we discuss the merits and shortcomings of these different approaches. In contrast, there were no significant
relationships between any color metrics and the carotenoid content of zebra finch beaks, suggesting that other color-generating
mechanisms besides carotenoids may contribute to color variability in this species. 相似文献
6.
7.
Rebecca K. James Christopher D. Hepburn Christopher E. Cornwall Christina M. McGraw Catriona L. Hurd 《Marine Biology》2014,161(7):1687-1696
The sustained absorption of anthropogenically released atmospheric CO2 by the oceans is modifying seawater carbonate chemistry, a process termed ocean acidification (OA). By the year 2100, the worst case scenario is a decline in the average oceanic surface seawater pH by 0.3 units to 7.75. The changing seawater carbonate chemistry is predicted to negatively affect many marine species, particularly calcifying organisms such as coralline algae, while species such as diatoms and fleshy seaweed are predicted to be little affected or may even benefit from OA. It has been hypothesized in previous work that the direct negative effects imposed on coralline algae, and the direct positive effects on fleshy seaweeds and diatoms under a future high CO2 ocean could result in a reduced ability of corallines to compete with diatoms and fleshy seaweed for space in the future. In a 6-week laboratory experiment, we examined the effect of pH 7.60 (pH predicted to occur due to ocean acidification just beyond the year 2100) compared to pH 8.05 (present day) on the lateral growth rates of an early successional, cold-temperate species assemblage dominated by crustose coralline algae and benthic diatoms. Crustose coralline algae and benthic diatoms maintained positive growth rates in both pH treatments. The growth rates of coralline algae were three times lower at pH 7.60, and a non-significant decline in diatom growth meant that proportions of the two functional groups remained similar over the course of the experiment. Our results do not support our hypothesis that benthic diatoms will outcompete crustose coralline algae under future pH conditions. However, while crustose coralline algae were able to maintain their presence in this benthic rocky reef species assemblage, the reduced growth rates suggest that they will be less capable of recolonizing after disturbance events, which could result in reduced coralline cover under OA conditions. 相似文献
8.
Carlos Navarro Tomás Pérez-Contreras Jesús M. Avilés Kevin J. McGraw Juan J. Soler 《Behavioral ecology and sociobiology》2010,64(7):1209-1067
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. 相似文献
9.
In egg-laying animals, mothers can influence the development of their offspring via the suite of biochemicals they incorporate
into the nourishing yolk (e.g. lipids, hormones). However, the long-lasting fitness consequences of this early nutritional
environment have often proved elusive. Here, we show that the colorful carotenoid pigments that female zebra finches (Taeniopygia guttata) deposit into egg yolks influence embryonic and nestling survival, the sex ratio of fledged offspring, and the eventual ornamental
coloration displayed by their offspring as adults. Mothers experimentally supplemented with dietary carotenoids prior to egg-laying
incorporated more carotenoids into eggs, which, due to the antioxidant activity of carotenoids, rendered their embryos less
susceptible to free-radical attack during development. These eggs were subsequently more likely to hatch, fledge offspring,
produce more sons than daughters, and produce sons who exhibited more brightly colored carotenoid-based beak pigmentation.
Provisioned mothers also acquired more colorful beaks, which directly predicted levels of carotenoids found in eggs, thus
indicating that these pigments may function not only as physiological ‘damage-protectants’ in adults and offspring but also
as morphological signals of maternal reproductive capabilities. 相似文献
10.
Patterns of courtship behavior and ejaculate characteristics in male red-winged blackbirds 总被引:1,自引:0,他引:1
David F. Westneat Lisa A. McGraw Jennifer M. Fraterrigo Tim R. Birkhead F. Fletcher 《Behavioral ecology and sociobiology》1998,43(3):161-171
Sperm competition in birds is likely to have important effects on the behavior and physiology of reproduction in both sexes.
For males, such competition should select for large sperm reserves and behavioral adjustment of copulation when reserves are
low. We investigated both these possibilities in free-living red-winged blackbirds (Agelaius phoeniceus), a highly polygynous species with apparently strong sperm competition. We found that the recent copulatory behavior of males
did not affect the propensity to copulate with a model female. Ejaculates collected from individual males at 1-h intervals
showed no evidence of sperm depletion, yet repeated ejaculates collected less than 10 min apart did. Male ejaculate size was
significantly larger if it was the first one of the day (i.e., after an overnight rest). The average ejaculate size was 12.5
(±12.5 SD) million sperm. Males captured during the breeding season had an average of 111.7 (±52.8) million sperm stored in
their seminal glomera. Because males average a peak copulation rate of six per female per day, in one day a male might utilize
all the sperm in his seminal glomera if more than two females on his territory are fertilizable. We hypothesize that polygyny
and sperm competition in this species have combined to select for rapid replenishment of the seminal glomera throughout the
day, in contrast to other species that have been studied. Testis size and sperm reserves of male red-winged blackbirds are
intermediate between monogamous species and species with intense sperm competition. Several possible explanations for this
are discussed.
Received: 21 October 1997 / Accepted after revision: 15 February 1998 相似文献