Roulin Alexandre, Richner Heinz, Ducrest Anne-Lyse
Department of Zoology, University of Bern, Wohlenstrasse 50a, CH-3032, Hinterkappelen, Switzerland.
Evolution. 1998 Oct;52(5):1451-1460. doi: 10.1111/j.1558-5646.1998.tb02026.x.
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.
第二性征被认为能够指示个体质量。奢侈状态下的限性性状表达可能既需要潜在基因，也需要可用的营养资源。评估基因、环境和身体状况的相对贡献，对于理解奢侈性状在多大程度上可能标志着个体的基因型或表型质量至关重要。在鸟类中，通常只有雄性具有装饰性。在仓鸮（Tyto alba）中，雌性和雄性都表现出限性羽毛特征。雄性通常颜色较浅，雌性则斑点较多。在一项结合了交叉寄养和窝雏大小操纵的实验中，我们确定了基因、环境和身体状况对羽毛颜色和羽毛斑点变化的相对贡献。部分交叉寄养实验测试了共享基因和共享环境对相关鸟类相似性的相对重要性。在不同巢穴中饲养的兄弟姐妹趋向于相似的性状值，后代与亲生父母而非养父母相似，并且共享同一巢穴的无亲缘关系雏鸟的羽毛性状不相关。结果没有因母亲表型中可检测到的母体效应而夸大，因为中间女儿与母亲的相似性并不高于中间儿子与父亲的相似性。这表明羽毛颜色和斑点在很大程度上是遗传性状，并且饲养环境对这些性状的表达没有强烈影响。为了进一步研究这两个限性性状是否依赖于身体状况，我们操纵了窝雏大小。将窝雏数量增加或减少两只分别导致雏鸟体重降低或增加。然而，在扩大或缩小的窝中饲养的雏鸟并没有表现出羽毛明显更暗或更亮，或者斑点更多或更少。我们没有检测到任何基因型与环境的相互作用。总之，同时进行交叉寄养和窝雏大小操纵表明，羽毛颜色和斑点的加性遗传方差得以维持，并且饲养环境和身体状况在雌性和雄性装饰的表型方差中所占比例不大。
