Pathways of lysozyme evolution inferred from the sequences of cytochrome b in birds

Abstract

A reliable phylogeny relating the major groups of Galliformes was sought in order to shed light on an unusual case of coupled amino acid replacements in the lysozymes c of these birds. The New World quail and the African guinea fowl share a unique trio of amino acids at three internal positions but have been separated phylogenetically by the majority of trees based on morphological characters. Alternative hypotheses based on molecular data have suggested an arrangement that would be more parsimonious with regard to the lysozyme data. The entire mitochondrial cytochrome b gene (1,143 bp) was amplified via the polymerase chain reaction (PCR) and sequenced for nine galliforms and a representative anseriform to provide DNA sequence data for a phylogenetic reconstruction. The mode and tempo of change in these sequences were analyzed to determine the characters most appropriate for phylogenetic reconstruction. Our results place the New World quail outside all other representative game birds except the cracids. Although in conflict with various morphological analyses, this finding is consistent with the results of DNA-DNA hybridization studies. A model to account for the coupled replacements in the lysozymes is presented. Our results also suggest a rapid but ancient radiation among the Galliformes such that the majority of cytochrome b sequence differences among taxa have accumulated on the terminal branches of the reconstructed phylogenetic trees.