Molecular evolution of genes in avian genomes

We found clear differences in the substitution rate at fourfold degenerate sites, being lowest in the ancestral bird lineage, intermediate in the chicken lineage and highest in the zebra finch lineage, possibly reflecting differences in generation time. We identified positively selected and/or rapidly evolving genes in avian lineages and found an over-representation of several functional classes, including anion transporter activity, calcium ion binding, cell adhesion and microtubule cytoskeleton.Focusing specifically on genes of neurological interest and genes differentially expressed in the unique vocal control nuclei of the songbird brain, we find a number of positively selected genes, including synaptic receptors. We found no evidence that selection for beneficial alleles is more efficient in regions of high recombination; in fact, there was a weak yet significant negative correlation between ω and recombination rate, which is in the direction predicted by the Hill-Robertson effect if slightly deleterious mutations contribute to protein evolution. These findings set the stage for studies of functional genetics of avian genes.There are nearly 10,000 known species of birds and many of these have been instrumental in studies of general aspects of behavior, ecology and evolution. Such basic knowledge on life history and natural history will become an important resource for studies aiming at elucidating the genetic background to phenotypic evolution in natural bird populations [1]. There have already been some attempts in this direction, including the demonstration that the calmodulin pathway is involved in the evolution of the spectacular differences in beak morphology among Darwin's finches [2,3] and the critical role of MC1R governing variation in plumage color in several bird species [4].At the genomic level, birds have attracted the attention of biologists for several reasons. First, compared to other vertebrates, avian genomes are compact, with estimated DNA co