Ta. Gorr et al., PHYLOGENETIC ANALYSIS OF REPTILIAN HEMOGLOBINS - TREES, RATES, AND DIVERGENCES, Journal of molecular evolution, 47(4), 1998, pp. 471-485
Phylogenetic relationships among reptiles were examined using previous
ly published and newly determined hemoglobin sequences. Trees reconstr
ucted from these sequences using maximum-parsimony, neighbor-joining,
and maximum-likelihood algorithms were compared with a phylogenetic tr
ee of Amniota, which was assembled on the basis of published morpholog
ical data. All analyses differentiated alpha chains into alpha(A) and
alpha(D) types, which are present in all reptiles except crocodiles, w
here only alpha(A) chains are expressed. The occurrence of the alpha(D
) chain in squamates (lizards and snakes only in this study) appears t
o be a general characteristic of these species. Lizards and snakes als
o express two types of beta chains (beta I and beta II), while only on
e type of beta chain is present in birds and crocodiles. Reconstructed
hemoglobin trees for both alpha and beta sequences did not yield the
monophyletic Archosauria (i.e., crocodilians + birds) and Lepidosauria
(i.e., Sphenodon + squamates) groups defined by the morphology tree.
This discrepancy, as well as some other poorly resolved nodes, might b
e due to substantial heterogeneity in evolutionary rates among single
hemoglobin lineages. Estimation of branch lengths based on uncorrected
amino acid substitutions and on distances corrected for multiple subs
titutions (PAM distances) revealed that relative rates for squamate al
pha(A) and alpha(D) chains and crocodilian beta chains are at least tw
ice as high as those of the rest of the chains considered. In contrast
to these rate inequalities between reptilian orders, little variation
was found within squamates, which allowed determination of absolute e
volutionary rates for this subset of hemoglobins. Rate estimates for h
emoglobins of lizards and snakes yielded 1.7 (alpha(A)) and 3.3 (beta)
million years/PAM when calibrated with published divergence time vs.
PAM distance correlates for several speciation events within snakes an
d for the squamate <-> sphenodontid split. This suggests that hemoglob
in chains of squamate reptiles evolved similar to 3.5 (alpha(A)) or si
milar to 1.7 times (beta) faster than their mammalian equivalents. The
se data also were used to obtain a first estimate of some intrasquamat
e divergence times.