Plumage and eggshell colouration covary with the level of sex-specific parental contributions to nest building in birds

AbstractInterspecific variation in sex-specific contributions to prenatal parental care, including avian nest building, is becoming increasingly better understood as we amass more information on more species. We examined whether sex-specific nest building contributions covary with the colouration of parents and their eggs in 521 species of Western Palearctic birds. Having colourful plumage and laying colourful eggs are costly because of the deposition of pigments in feathers and eggs and/or forming costly nanostructural substrates in feathers, and so it might be expected that those costs covary with the costs of nest building at the level of individuals and/or across species to produce of a suite of codivergent traits. Using a phylogenetically informed approach, we tested the first hypothesis which was that species in which females alone invest energy building nests exhibit less sexual plumage dichromatism, which is costlier for females because they are investing energy having brighter plumage and building nests than in species exhibiting sexual plumage dichromatism and found comparative support for the opposite of this prediction. We then tested a second hypothesis that species in which females alone build nests lay more colourful, and costlier, eggs because the dual costs of building nests and laying colourful eggs can only be borne by higher quality individuals. As expected, we found that species in which females build nests alone or together with males are more likely to lay colourfully pigmented eggs relative to species in which only males build nests. Finally, stochastic character mapping provided evidence of the repeated evolution of female-only nest building. Interspecific sex differences in plumage colouration therefore covary in a complex manner with female pre- (nest building) and post-copulatory (egg production) investment in reproduction.Usage notesVariable names and descriptionsSpecies - scientific name of bird speciesNest_builder - nest builder sex (both, female, male, neither)Colour_dichromatism - sexual plumage dichromatism (yes/no)Egg_colur - egg colouration (blue, brown, white)Maculation - egg maculation (yes/no)Nest_design - nest design (open/enclosed)Mean_BM - average adult body mass in gramsClutch_size_mean - average clutch size摘要 随着我们对更多鸟类物种积累了更为丰富的研究数据，包括鸟类筑巢行为在内的产前亲代抚育（parental care）的种间性别特异性贡献差异正逐步得到更为深入的阐释。本研究针对521种西古北界（Western Palearctic）鸟类，探究了性别特异性筑巢贡献与亲代及鸟卵的体色是否存在共变关系。体色艳丽的羽毛与色彩丰富的鸟卵均需付出适应性代价：这源于羽毛和鸟卵中的色素沉积，以及羽毛中昂贵的纳米结构基质形成过程。据此推测，这些代价与筑巢的代价可能在个体层面或跨物种类群间存在共变，进而形成一系列协同分化的性状。本研究采用系统发育比较分析（phylogenetically informed approach）方法，检验了第一个假说：仅由雌性投入能量筑巢的物种，其性羽色二态性（sexual plumage dichromatism）程度低于存在性羽色二态性的类群——因为相较于后者，雌性既要投入能量演化出艳丽羽色，又要筑巢，承担的代价更高。但研究结果却为该假说的反向预测提供了比较支持。随后我们检验了第二个假说：仅由雌性筑巢的物种会产下色彩更艳丽、代价更高的鸟卵，因为筑巢与产下艳丽鸟卵的双重代价，仅能由个体质量更高的类群承担。正如预期，我们发现：相较于仅由雄性筑巢的物种，由雌性单独筑巢或雌雄共同筑巢的类群更倾向于产下带有色素的彩色鸟卵。最后，随机性状映射（stochastic character mapping）分析结果为仅雌性筑巢的重复演化提供了证据。因此，鸟类羽色的种间性别差异，与雌性在繁殖前期（筑巢）及交配后（产卵）的繁殖投入存在复杂的共变关系。 使用说明 变量名称与说明 1. 物种：鸟类的科学学名 2. 筑巢者：负责筑巢的性别（雌雄共同、雌性、雄性、无） 3. 羽色二态性：性羽色二态性（是/否） 4. 卵色：鸟卵体色（蓝色、棕色、白色） 5. 卵斑：鸟卵是否具斑点（是/否） 6. 巢型：巢穴结构（开放式、封闭式） 7. 平均体重：成年个体平均体重，单位为克 8. 平均窝卵数：平均每窝产卵数