Nanostructural self-assembly of iridescent feather barbules through depletion attraction of melanosomes during keratinization
Nanostructural self-assembly of iridescent feather barbules through depletion attraction of melanosomes during keratinization
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DOI：
10.1098/rsif.2011.0456
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发表时间：
2012-04-07
影响因子：
3.9
通讯作者：
Shawkey, Matthew D.
中科院分区：
文献类型：
--
作者：
Maia, Rafael;Macedo, Regina H. F.;Shawkey, Matthew D.
鸟类羽毛的颜色是了解性选择观赏性状进化的模型性状。讽刺的是，彩虹色的结构色，可能是这些特征中最耀眼的，仍然是最缺乏了解的。虽然一些数据表明，表达明亮的虹彩羽毛颜色所产生的高度有序阵列的黑素体和角蛋白是条件依赖性的，几乎没有什么是已知的，他们的个体发育，因此任何发育机制，可能容易受到干扰。在这里，我们使用光学和电子显微镜比较个体发育的虹彩男性和非虹彩女性羽毛的蓝黑色草鸡。雄性的羽管含有一层黑素体，由一层产生蓝色彩虹色的角质层包围，而雌性的羽管含有混乱的黑素体，没有外层。我们发现，纳米结构组织的男性小须子发生在发展后期，死亡后的小须子细胞，因此不太可能是直接的细胞控制下，与以前的建议。相反，组织似乎是由熵驱动的自组装引起的，通过耗尽吸引力将黑素体固定在触须细胞的边缘并相互固定。这些力量可能在男性的毛囊发育中比女性更强，因为他们的黑素体（i）更大，（ii）更密集，（iii）由于角质化过程中毛囊形状更一致，分布更均匀。这些数据首次提出了虹彩羽毛颜色的发育途径，并表明虹彩羽毛的任何条件依赖性可能是由直接代谢成本以外的因素驱动的。
Avian plumage colours are model traits in understanding the evolution of sexually selected ornamental traits. Paradoxically, iridescent structural colours, probably the most dazzling of these traits, remain the most poorly understood. Though some data suggest that expression of bright iridescent plumage colours produced by highly ordered arrays of melanosomes and keratin is condition-dependent, almost nothing is known of their ontogeny and thus of any developmental mechanisms that may be susceptible to perturbation. Here, we use light and electron microscopy to compare the ontogeny of iridescent male and non-iridescent female feathers in blue-black grassquits. Feather barbules of males contain a single layer of melanosomes bounded by a thin layer of keratin-producing blue iridescent colour, while those of females contain disorganized melanosomes and no outer layer. We found that nanostructural organization of male barbules occurs late in development, following death of the barbule cell, and is thus unlikely to be under direct cellular control, contrary to previous suggestions. Rather, organization appears to be caused by entropically driven self-assembly through depletion attraction forces that pin melanosomes to the edge of barbule cells and to one another. These forces are probably stronger in developing barbules of males than of females because their melanosomes are (i) larger, (ii) more densely packed, and (iii) more homogeneously distributed owing to the more consistent shape of barbules during keratinization. These data provide the first proposed developmental pathway for iridescent plumage colours, and suggest that any condition dependence of iridescent barbules is likely driven by factors other than direct metabolic cost.