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. 2008 May 21;3(5):e2201. doi: 10.1371/journal.pone.0002201

Figure 1. Mitochondrial proteins have experienced extraordinarily elevated rates of amino acid replacement early in the evolution of snakes.

Figure 1

The conservative transversion-based approximations of the relative rates of non-synonymous to synonymous substitution (dN TV12 / dS TV4x) rates are shown as open or colored circles for each branch of the phylogenetic tree; linear regression lines (excluding points in the red ellipse) are shown in black (A and B). The calculations shown are from (A) all mitochondrial proteins and (B) cytochrome C oxidase subunit 1 (COI). Blue-shaded areas of A and B indicate very long branches with high dS TV4x values where the (dN TV12 / dS TV4x) estimate may be inaccurate, possibly due to dS TV4x saturation and underestimation. Note that early snake branches have very high dN TV12, far greater than branches of comparable length (dS TV4x). This is strong evidence for extraordinarily accelerated rates of amino acid replacement early in snake evolution. The phylogenetic tree of relationships among species in our comparative dataset is shown in (C). Branches with extremely high values of dN TV12 / dS TV4X for COI are indicated with colored lines (black, blue, red) following the key in the bottom left. The circles for branches in (A) and (B) were colored according to the same legend for ratios of COI (dN TV12 / dS TV4x).