Meeting Abstract
Feathers exhibit an extraordinary diversity of shapes and sizes, which are used by birds to accomplish a diverse set of functions. Pennaceous feathers have a complex branched morphology that develops from a tube of epidermis, and variation in branch geometry and morphology determines the shape and structure of feathers. Feather development is complex and mechanistically redundant, and it is not readily obvious 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 have important affects on the shape of mature feathers but the development of barb curvature is unknown. Prum and Williamson (2001) hypothesized that barb curvature develops during barb ridge growth in the tubular feather germ, whereas Feo and Prum (2014) hypothesized that barb curvature develops during barb ramus expansion as the feather unfurls from the sheath. To better understand the development of barb curvature and its effects on feather morphology we first present a theoretical model of barb curvature and then conduct empirical observations of barb curvature in mature and developing feathers. We find that barb curvature can have complex effects on many aspects of feather morphology including vane width, barb length, interbarb distance, and barb ridge width. In real feathers, barbs curve both during barb ridge growth and during barb expansion, with most of the observed curvature developing during barb expansion. Our results demonstrate that barb expansion as the feather unfurls from the sheath is a complex and dynamic process that varies within a feather vane and plays an important role in determining mature feather shape. Barb curvature results in heterogeneity of barb geometry within a feather vane, which could have important implications for the mechanical function of feathers and within feather pigmentation patterns.
