Cytochrome b Nucleotide Sequence Variation Among the Atlantic Alcidae

Analysis of Cytochrome b nucleotide sequences of the six extant species of Atlantic alcids and a gull revealed an excess of adenines and cytosines and a deficit of guanines at silent sites on the coding strand. Phylogenetic analyses grouped the sequences of the common ( Uria aalge ) and Brünnich's ( U. lomvia ) guillemots, followed by the razorbill ( Alca torda ) and little auk ( Alle alle ). The black guillemot ( Cepphus grylle ) sequence formed a sister taxon, and the puffin ( Fratercula arctica ) fell outside the other alcids. Phylogenetic comparisons of substitutions indicated that mutabilities of bases did not differ, but that C was much more likely to be incorporated than was G. Imbalances in base composition appear to result from a strand bias in replication errors, which may result from selection on secondary RNA structure and/or the energetics of codon‐anticodon interactions.