Molecular basis of hemoglobin adaptation in the high-flying bar-headed goose
Fig 1
Inferred history of amino acid substitution at five sites that distinguish the major Hb isoforms of the bar-headed goose (Anser indicus) and greylag goose (Anser anser).
(A) Amino acid states at the same sites are shown for 12 other waterfowl species in the subfamily Anserinae. Of the five amino acid substitutions that distinguish the Hbs of A. indicus and A. anser, parsimony indicates that three occurred on the branch leading to A. indicus (αG18S, αA63V, and αP119A) and two occurred on the branch subtending the clade of all Anser species other than A. indicus (βT4S and βD125E). ‘AncAnser’ represents the reconstructed sequence of the A. indicus/A. anser common ancestor, which is also the most recent common ancestor of all extant species in the genus Anser. (B) Triangulated comparisons involving rHbs of bar-headed goose, greylag goose, and their reconstructed ancestor (AncAnser) reveal the polarity of changes in character state. Differences in Hb function between bar-headed goose and AncAnser reflect the net effect of three substitutions (αG18S, αA63V, and αP119A) and differences between greylag goose and AncAnser reflect the net effect of two substitutions (βT4S and βD125E). All possible mutational intermediates connecting AncAnser with each of the two descendent species are shown to the side of each terminal branch (the sequential order of the substitutions is unknown, so the order in which they are shown on each terminal branch is arbitrary).