Faculty & Staff Directory
Executive Dean, College of Arts and Sciences
Department of Biology
University of South Carolina
|Office:||Gambrell Hall 251||Phone Number:||803 777 7161||Email:||email@example.com|
Studies of the Development and Evolutionary Origins of Reptilian and Avian Epidermal Appendages (scales, claws, beaks and feathers) using Comparative Genomics and Molecular Phylogenies.Remarkable fossils of theropod dinosaurs displaying a wide range of epidermal structures (Fucheng et al., 2006; Ortega et al., 2010) have been discovered in the past two decades. The "four-winged" theropod, Anchiornis huxleyi (dated ~ 155 Million years ago [Ma]) shows that extensive feathering including pennaceous wing and leg feathers was present by the early Late Jurassic (Hu et al., 2009), implying that the evolutionary origin of feathers occurred before this time.
The epidermal appendages of extant reptiles and birds, such as scales, claws and feathers, are constructed of beta (β) keratin, a unique fibrous protein, in which a filament-matrix structure is formed by each single β-keratin molecule, unlike the situation in mammalian epidermal appendages where alpha (α) keratin molecules interact with distinct matrix molecules to form cornified appendages, such as hair (see Fraser and Parry, 2008, 2010). The amino acid sequence (31-32 residues) of the central filament region of β-keratins is highly conserved throughout all reptiles and birds suggesting that this domain has changed little in ~285 Ma of evolution (Fraser and Parry, 2010).
In birds, the β-keratin multigene family has diverged into four major subfamilies, scale, claw, feather-like, and feather (Presland et al., '89 a, b). As the genomes of birds become available (i.e., chicken, turkey, and zebra finch), comparative studies of the genomic organization of the β keratin subfamilies provide information on how the genotype influences phenotype (Greenwold and Sawyer, 2010).
Furthermore, phylogenetic analyses of the avian β-keratin genes from the chicken and zebra finch genomes have shown that the avian scale β-keratin subfamily is closely related to the β-keratins of crocodilians and basal to the claw β-keratin subfamily, which is basal to the feather-like and feather β-keratin subfamilies (Greenwold and Sawyer, 2010).
Presently we are using molecular dating approaches, such as BEAST, to gain a better understanding of the how the molecular evolution of the avian β-keratins relates to the evolutionary origin of feathers. Our approach is to combine molecular dating techniques with knowledge of the sauropsid fossil record, feather development, molecular evolution of the avian β-keratins, and the biophysical properties of feathers to gain a better understanding of feather evolution.
Greenwold and Sawyer (2011) demonstrate that the basal β-keratins of birds began diverging from their archosaurian ancestor ~216 million years ago, while the subfamily of feather β-keratins, as found in living birds, began diverging ~143 million years ago. Thus the evolutionary origin of feathers does not coincide with the molecular evolution of feather β-keratins found in modern birds. Recent biophysical studies of the β-keratins in today's feathers support the view that the appearance of the subfamily of feather β-keratins altered the biophysical nature of the feather establishing its role in powered flight.
Post Doctoral Fellow:
Greenwold MJ, Sawyer RH. 2013. Molecular evolution and expression of
archosaurian b‐keratins: Diversification and expansion of archosaurian β‐keratins and the
origin of feather β‐keratins. J. Exp. Zool. (Mol. Dev. Evol.) 320B:393–405.
John A. St. John et al.. 2012. Sequencing three crocodilian genomes to illuminate the evolution of archosaurs and amniotes.. Genome Biology. 13: 415. St John et al. Genome Biology 2012, 13:415
Matthew J. Greenwold and Roger H. Sawyer. 2011. Linking the molecular evolution of avian beta keratins to the evolution of feathers.. J. Exp. Zool (Mol. Dev. Evol.) . 316B: 609-616. Wiley Online Library
Matthew J. Greenwold and Roger H. Sawyer. 2010. Genomic organization and molecular phylogenies of the beta keratin multigene family in the chicken (Gallus gallus) and zebra finch (Taeniopygia guttata): implications for feather evolution.. BMC Evolutionary Biology. 10:148. Greenwold and Sawyer BMC Evolutionary Biology 2010, 10:148