Characterization of melanosomes involved in the production of non-iridescent structural feather colours and their detection in the fossil record
Characterization of melanosomes involved in the production of non-iridescent structural feather colours and their detection in the fossil record
复制标题
DOI：
10.1098/rsif.2018.0921
复制
发表时间：
2019-06-01
影响因子：
3.9
通讯作者：
Vinther, Jakob
中科院分区：
文献类型：
--
作者：
Babarovic, Frane;Puttick, Mark N.;Vinther, Jakob
鸟类羽毛中的非彩虹结构颜色是通过倒钩的角蛋白皮质中准有序的纳米腔的相干光散射而产生的。为了吸收未散射的光，黑素小体在纳米腔下面形成了一层基底层。研究表明，在整个Aves中，黑素小体的形态反映了广泛的基于黑色素的着色以及彩虹，从而能够在保存异常完好的化石中识别出古老的彩色。然而，目前还没有关于非虹彩结构颜色的黑素小体的形态的研究。在这里，我们分析了大量的羽毛中表达非虹彩结构颜色的羽毛黑素小体样本，以描述它们的形态并与其他鸟类黑素小体类别进行比较。我们发现，所研究的黑素小体通常很宽(约300纳米)和长(约1400 nm)，有别于黑色、棕色和彩虹色羽毛中的黑素小体，但与灰色羽毛中的黑素小体显著重叠。这可能暗示了灰色和非虹彩结构颜色之间的发展关系，甚至可能是进化关系。我们发现，通过对化石黑素小体的分析，可以在始新世的茎群中预测出指示非虹彩结构颜色的黑素小体(Eocoracas：Coraciformes)，并通过系统发育比较的方法推测可能的色调。来自灰色和非虹彩结构有色羽毛的黑素体之间的重叠使它们在角蛋白不保存的化石样本中的区分变得复杂。然而，相对于非虹彩的结构色彩，灰色色彩的丰富使得前者更有可能发生，除非是在系统发育上有支架的标本中，如这里研究的Eocoracas标本。
Non-iridescent structural colour in avian feathers is produced by coherent light scattering through quasi-ordered nanocavities in the keratin cortex of the barbs. To absorb unscattered light, melanosomes form a basal layer underneath the nanocavities. It has been shown that throughout Aves, melanosome morphology reflects broad categories of melanin-based coloration, as well as iridescence, allowing identification of palaeocolours in exceptionally preserved fossils. However, no studies have yet investigated the morphology of melanosomes in non-iridescent structural colour. Here, we analyse a wide sample of melanosomes from feathers that express non-iridescent structural colour from a phylogenetically broad range of extant avians to describe their morphology and compare them with other avian melanosome categories. We find that investigated melanosomes are typically wide (approx. 300 nm) and long (approx. 1400 nm), distinct from melanosomes found in black, brown and iridescent feathers, but overlapping significantly with melanosomes from grey feathers. This may suggest a developmental, and perhaps evolutionary, relationship between grey coloration and non-iridescent structural colours. We show that through analyses of fossil melanosomes, melanosomes indicative of non-iridescent structural colour can be predicted in an Eocene stem group roller (Eocoracias: Coraciiformes) and with phylogenetic comparative methods the likely hue can be surmised. The overlap between melanosomes from grey and non-iridescent structurally coloured feathers complicates their distinction in fossil samples where keratin does not preserve. However, the abundance of grey coloration relative to non-iridescent structural coloration makes the former a more likely occurrence except in phylogenetically bracketed specimens like the specimen of Eocoracias studied here.