Feo Teresa J, Simon Emma, Prum Richard O
Department of Ecology and Evolutionary Biology, Yale University, New Haven, Connecticut.
Peabody Museum of Natural History, Yale University, New Haven, Connecticut.
J Morphol. 2016 Aug;277(8):995-1013. doi: 10.1002/jmor.20552. Epub 2016 May 17.
Feathers exhibit an extraordinary diversity of shapes, which are used by birds to accomplish a diverse set of functions. Pennaceous feathers have a double branched morphology that develops from a tube of epidermis, and variation in branch geometry determines feather shape. Feather development is both complex (i.e., a simple developmental modification can have multiple effects on mature feather shape), and redundant (i.e., different developmental modifications can create the same shape). Due to this, it is not readily apparent how different feather shapes develop. In many feathers, barbs are not straight, but instead curve in toward, or away, from the feather tip. Barb curvature can affect the shape of mature feathers but the development of curved barbs is unknown. Previous research has hypothesized that barb curvature could develop either during the helical growth of barb ridges in the tubular feather germ, or during barb angle expansion as the feather unfurls from the sheath. To better understand the development of curved barbs and their effects on mature feathers we present a theoretical model of curved barb development and test the model with empirical investigations of feathers. We find that curved barbs affect many aspects of feather morphology including vane width, barb length, and barb spacing. In real feathers, curved barbs can develop both during helical barb ridge growth and during barb angle expansion, with most of the observed curvature due to barb angle expansion. Our results demonstrate that barb angle expansion as a feather unfurls from the sheath is a complex and dynamic process that plays an important role in determining the shape and structure of mature feathers. Curved barbs create heterogeneity in barb geometry within the feather vane, which could have important implications for aerodynamic function and the development of within feather pigmentation patterns. J. Morphol. 277:995-1013, 2016. © 2016 Wiley Periodicals, Inc.
羽毛呈现出极其多样的形状，鸟类利用这些形状来完成一系列不同的功能。正羽具有双分支形态，由表皮管发育而来，分支几何结构的变化决定了羽毛的形状。羽毛发育既复杂（即一个简单的发育改变可能对成熟羽毛形状产生多种影响）又冗余（即不同的发育改变可能产生相同的形状）。因此，不同羽毛形状是如何发育的并不明显。在许多羽毛中，羽支不是直的，而是朝着或远离羽尖弯曲。羽支曲率会影响成熟羽毛的形状，但弯曲羽支的发育尚不清楚。先前的研究推测，羽支曲率可能在管状羽胚中羽支嵴的螺旋生长过程中形成，或者在羽毛从羽鞘展开时羽支角度扩展过程中形成。为了更好地理解弯曲羽支的发育及其对成熟羽毛的影响，我们提出了一个弯曲羽支发育的理论模型，并通过对羽毛的实证研究来测试该模型。我们发现弯曲羽支会影响羽毛形态的许多方面，包括羽片宽度、羽支长度和羽支间距。在实际的羽毛中，弯曲羽支可以在羽支嵴螺旋生长过程中以及羽支角度扩展过程中形成，观察到的大部分曲率是由于羽支角度扩展造成的。我们的结果表明，羽毛从羽鞘展开时的羽支角度扩展是一个复杂而动态的过程，在决定成熟羽毛的形状和结构方面起着重要作用。弯曲羽支在羽片内的羽支几何结构中产生了异质性，这可能对空气动力学功能以及羽毛内部色素沉着模式的发育具有重要意义。《形态学杂志》277:995 - 1013, 2016。© 2016威利期刊公司
