Patterning and microstructure of penguin plumage
Penguins (Sphenisciformes) exhibit an array of derived feather features. The characters describing penguin integument that are used in the phylogenetic reconstruction have not been reassessed since they were written in 2005. I reassessed all integument characters for extant penguins and outgroup taxa. The phylogenetic tree constructed using the reassessed integument characters does not differ in topology from the original phylogenetic tree except that several outgroup relationships become less resolved. This indicates that conclusions drawn by previous authors about the relationships among extant penguins using the original tree are still valid. However, the reconstruction of the integument of the common ancestor of Spheniscidae no longer remains the same. Caution should be exercised when using museum bird skins to score integument characters because these colors can change over time, especially in the bill and legs. In addition to examining macro characteristics of penguin feathers, I also examined the microstructure of Gentoo Penguin (Pygoscelis papua) feathers in order to assess the presence of nanofibers, which had thus far only been found in the Little Penguin (Eudyptula minor). Nanofibers create the structural blue color in the dorsal feathers in the Little Penguin. I discovered nanofibers in all pigmented feathers in the Gentoo Penguin. The nanofibers in black parts of the feathers are overprinted by melanosomes. An amorphous keratin matrix exists in the white breast feathers, creating white structural color, but nanofibers are absent. My data suggest that penguin integument is even more modified relative to other birds than previously thought. Implications for penguin color patterning are presented concerning countershading and intraspecific signaling. The data presented in my study raise new questions about the origin and potential functions of penguin plumage structure and coloration.