GENETIC,ENVIRONMENTAL, AND CONDITION-DEPENDENT EFFECTS ON FEMALE AND MALE ORNAMENTATION IN THE BARN OWL TYTO ALBA

Secondary sexual characters are thought to indicate individual quality. Expression of sex-limited traits in an extravagant state may require both the underlying genes and the available nutrient resources. The assessment of the relative contribution of genes, environment, and body condition is relevant for understanding to that extent the extravagant trait may signal genotypic or phenotypic quality of the individual. In birds, usually only the males are ornamented. In the barn owl, Tyto alba, both females and males display sex-limited plumage traits. Males are commonly lighter colored and females spottier. In an experiment with combined cross-fostering and brood size manipulation we determined the relative contribution of genes, environment, and body condition to the variation in plumage coloration and plumage spottiness. The partial cross-fostering experiment tested the relative importance of shared genes and a shared environment for the resemblance of related birds. Siblings raised in different nests converged toward similar trait values, offspring resembled the true but not the foster parents, and plumage traits of unrelated nestlings sharing the same nest were not correlated. Results were not inflated by maternal effects detectable in the mother's phenotype, because middaughter to mother resemblance was not higher than midson to father resemblance. This suggests that plumage coloration and spottiness are largely genetically inherited traits, and that the rearing environment does not have a strong impact on the expression of these traits. To further investigate whether the two sex-limited traits are condition dependent, brood sizes were manipulated. Enlargement or reduction of broods by two nestlings resulted in lower and higher body mass of nestlings, respectively. However, nestlings raised in enlarged or reduced broods did not show either a significantly darker or lighter or a more or less spotted plumage. We did not detect any genotype-by-environment interaction. In conclusion, simultaneous cross-fostering and brood size manipulation demonstrate that additive genetic variance for plumage coloration and spottiness is maintained and that both the rearing environment and body condition do not account for a large proportion of the phenotypic variance in female and male ornamentations.     

Different modes of evolution in males and females generate dichromatism in fairy‐wrens (Maluridae)

Sexual dichromatism in birds is often attributed to selection for elaboration in males. However, evolutionary changes in either sex can result in plumage differences between them, and such changes can result in either gains or losses of dimorphism. We reconstructed the evolution of plumage colors in both males and females of species in Maluridae, a family comprising the fairy‐wrens (Malurus, Clytomias, Sipodotus), emu‐wrens (Stipiturus), and grasswrens (Amytornis). Our results show that, across species, males and females differ in their patterns of color evolution. Male plumage has diverged at relatively steady rates, whereas female coloration has changed dramatically in some lineages and little in others. Accordingly, in comparisons against evolutionary models, plumage changes in males best fit a Brownian motion (BM) model, whereas plumage changes in females fit an Ornstein Uhlenbeck (OU) multioptimum model, with different adaptive peaks corresponding to distributions in either Australia or New Guinea. Levels of dichromatism were significantly associated with latitude, with greater dichromatism in more southerly taxa. Our results suggest that current patterns of plumage diversity in fairy‐wrens are a product of evolutionary changes in both sexes, driven in part by environmental differences across the distribution of the family.     

Visual modelling suggests a weak relationship between the evolution of ultraviolet vision and plumage coloration in birds

Birds have sophisticated colour vision mediated by four cone types that cover a wide visual spectrum including ultraviolet (UV) wavelengths. Many birds have modest UV sensitivity provided by violet‐sensitive (VS) cones with sensitivity maxima between 400 and 425 nm. However, some birds have evolved higher UV sensitivity and a larger visual spectrum given by UV‐sensitive (UVS) cones maximally sensitive at 360–370 nm. The reasons for VS–UVS transitions and their relationship to visual ecology remain unclear. It has been hypothesized that the evolution of UVS‐cone vision is linked to plumage colours so that visual sensitivity and feather coloration are ‘matched’. This leads to the specific prediction that UVS‐cone vision enhances the discrimination of plumage colours of UVS birds while such an advantage is absent or less pronounced for VS‐bird coloration. We test this hypothesis using knowledge of the complex distribution of UVS cones among birds combined with mathematical modelling of colour discrimination during different viewing conditions. We find no support for the hypothesis, which, combined with previous studies, suggests only a weak relationship between UVS‐cone vision and plumage colour evolution. Instead, we suggest that UVS‐cone vision generally favours colour discrimination, which creates a nonspecific selection pressure for the evolution of UVS cones.     

Evolution of Dendrocolaptes platyrostris (Aves: Furnariidae) between the South American open vegetation corridor and the Atlantic forest

The open vegetation corridor of South America is a region dominated by savanna biomes. It contains forests (i.e. riverine forests) that may act as corridors for rainforest specialists between the open vegetation corridor and its neighbouring biomes (i.e. the Amazonian and Atlantic forests). A prediction for this scenario is that populations of rainforest specialists in the open vegetation corridor and in the forested biomes show no significant genetic divergence. We addressed this hypothesis by studying plumage and genetic variation of the Planalto woodcreeper Dendrocolaptes platyrostris Spix (1824) (Aves: Furnariidae), a forest specialist that occurs in both open habitat and in the Atlantic forest. The study questions were: (1) is there any evidence of genetic continuity between populations of the open habitat and the Atlantic forest and (2) is plumage variation congruent with patterns of neutral genetic structure or with ecological factors related to habitat type? We used cytochrome b and mitochondrial DNA control region sequences to show that D. platyrostris is monophyletic and presents substantial intraspecific differentiation. We found two areas of plumage stability: one associated with Cerrado and the other associated with southern Atlantic Forest. Multiple Mantel tests showed that most of the plumage variation followed the transition of habitats but not phylogeographical gaps, suggesting that selection may be related to the evolution of the plumage of the species. The results were not compatible with the idea that forest specialists in the open vegetation corridor and in the Atlantic forest are linked at the population level because birds from each region were not part of the same genetic unit. Divergence in the presence of gene flow across the ecotone between both regions might explain our results. Also, our findings indicate that the southern Atlantic forest may have been significantly affected by Pleistocene climatic alteration, although such events did not cause local extinction of most taxa, as occurred in other regions of the globe where forests were significantly affected by global glaciations. Finally, our results neither support plumage stability areas, nor subspecies as full species. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 103 , 801–820.     

Causes and consequences of individual variation in the extent of post‐juvenile moult in the blue tit Cyanistes caeruleus (Passeriformes: Paridae)

Moult, comprising the growth or replacement of feathers in birds, is an energetically demanding process. As a result, in many species, the extent of the post‐juvenile moult can vary substantially. However, the reasons underlying this variation remain poorly understood, and the potential life‐history consequences of variation in moult extent are even less clear. In the present study, we aimed to use individual‐specific data to identify factors affecting the extent of the post‐juvenile moult in a population of over 2500 blue tits Cyanistes caeruleus Linnaeus 1758, and to assess the consequences of individual variation in moult extent on reproduction in the first year of life. There was a substantial sex difference in post‐juvenile moult extent, with males moulting more extensively than females. Putative immigrant birds had moulted on average less than those born locally. However, there was little evidence of carry‐over effects of the natal environment on moult extent because we found no relationship between moult extent and fledging date or nestling mass. Evidence that moult extent, and hence feather brightness, affected subsequent reproductive success was limited. Moult extent had no effect on recruitment in males, although female recruits had moulted significantly less than nonbreeders. Because it was not influenced by features of the natal environment, moult extent may not be an honest signal of individual quality in C. caeruleus. As a result, the potential consequences of variation in moult extent for fitness are likely to be small.     

黄喉鹀的羽色与雄鸟质量相关性分析

在国内首次利用光纤光谱仪对鸟类的羽色进行量化和分析.对黄喉鹀Emberiza elegans雌、雄鸟羽色的差异以及雄鸟羽色与雄鸟质量的相关性分析结果表明,黄喉鹀雌、雄鸟在人眼看来相同的黄色羽和白色羽部分,在紫外光色度上却存在显著差异,雄鸟紫外光色度高于雌鸟;雄鸟的质量与脸部黑色羽的亮度、可见光色度和色调呈显著正相关,雌...     

鸟类羽色多态现象：概念及其进化机制假说

多态现象对了解物种的遗传、变异和进化有着重要意义,鸟类羽色多态现象的进化机制,是多态现象研究中非常重要的内容。鸟类羽色多态现象的进化机制假说主要有：分化选择假说、异类选择假说和非随机性交配假说等。本文对鸟类羽色多态现象的概念和以上进化机制假说进行了综述,并针对鸟类羽色多态现象进化机制研究中存在争议的问题及研究的不足提出了自己的看法。     

Dietary mineral content influences the expression of melanin-based ornamental coloration

Many animals develop bold patches of black or brown colorationthat are derived from melanin pigments and serve as sexual orsocial signals. At present, there is much debate among behavioralecologists over whether melanin-based color signals are costlyto produce. Studies that have manipulated crude aspects of nutrition(i.e., total food intake) or health have generally found melanin-basedplumage ornaments to be less responsive to such factors thanother types of extravagant color (e.g., carotenoid or structuralbased). However, a recently advanced hypothesis argues thatlimited minerals in the diet, such as calcium (Ca), zinc (Zn),and iron (Fe), may serve to increase melanin pigment productionand maintain signal honesty. Here, I experimentally tested whethervariation in the calcium content of the diet affects the colorand extent of melanin-based plumage in male zebra finches (Taeniopygiaguttata). Calcium supplementation increased the size, but notdarkness, of the black breast plumage patch in fledgling andadult males; however, sexually selected, carotenoid-based redbeak coloration was not affected by the diet manipulation. Theseresults are the first to support the idea that acquisition ofminerals from the diet is a unique, limiting factor for theexpression of ornamental melanin coloration in animals.     

Juvenile pheomelanin-based plumage coloration has evolved more frequently in carnivorous species

Distinctive pheomelanin-based plumage coloration in juvenile birds has been proposed as a signal of immaturity to avoid aggression by older conspecifics, but recent findings suggest a detoxifying strategy. Pheomelanin synthesis implies the consumption of cysteine, a semi-essential amino acid that is necessary for the synthesis of the antioxidant glutathione (GSH) but that may be toxic if in excess in the diet. As the nestling stage probably represents a low-stress period with limited requirement for GSH protection, the synthesis of pheomelanin in developing birds may help to maintain cysteine homeostasis, particularly in species with a high content of protein in the diet (i.e. carnivores). Here we confirm this hypothesis showing that, among 53 species of Western Palaearctic birds, juvenile pheomelanin-based coloration has evolved more frequently in strictly carnivorous species than in species with other diets.     

Morph‐dependent fitness and directional change of morph frequencies over time in a Dutch population of Common buzzards Buteo buteo

How genetic polymorphisms are maintained in a population is a key question in evolutionary ecology. Previous work on a plumage colour polymorphism in the common buzzard Buteo buteo suggested heterozygote advantage as the mechanism maintaining the co‐existence of three morphs (light, intermediate and dark). We took advantage of 20 years of life‐history data collected in a Dutch population to replicate earlier studies on the relationship between colour morph and fitness in this species. We examined differences between morphs in adult apparent survival, breeding success, annual number of fledglings produced and cumulative reproductive success. We found that cumulative reproductive success differed among morphs, with the intermediate morph having highest fitness. We also found assortative mating for colour morph, whereby assortative pairs were more likely to produce offspring and had longer‐lasting pair bonds than disassortative pairs. Over the 20‐year study period, the proportion of individuals with an intermediate morph increased. This apparent evolutionary change did not just arise from selection on individual phenotypes, but also from fitness benefits of assortative mating. The increased frequency of intermediates might also be due to immigration or drift. We hypothesize that genetic variation is maintained through spatial variation in selection pressures. Further studies should investigate morph‐dependent dispersal behaviour and habitat choice.