Adaptive molecular convergences

Abstract

Definitive identification of convergent evolution, the acquisition of the same biological trait in unrelated lineages, provides one of the most compelling sources of evidence for natural selection. Although numerous examples of convergent morphological evolution are well known (such as the independent development of wings in birds and mammals), cases of convergent evolution at the molecular-genetic level appear to be quite rare. We recently discovered a remarkable case of convergent molecular evolution involving more than 100 parallel amino-acid changes across all 13 mitochondrially-encoded proteins of snakes and agamid lizards. Just a few of these convergent substitutions were sufficient to positively mislead the inference of phylogeny, even with thousands of sites providing latent support for the correct underlying relationships. Since this example demonstrates that molecular convergence can happen en masse in nature, affecting multiple genes, it is important to consider the threat this poses to molecular systematics, and careful genome-wide assays for convergent molecular evolution are warranted. This result implies that the protein adaptive landscape is sometimes highly constrained.

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Acknowledgements

We are thankful for the support of the National Institutes of Health (NIH R01 GM083127) to D.D.P., and an NIH training grant (LM009451) to T.A.C.

Figures and Tables

Figure 1 Alternative views of potential protein adaptive landscapes. In (A), the protein adaptive landscape is viewed as being like an arrêt ridge, with only a single narrow path leading from the current adaptive peak in the foreground to a new adaptive peak in the distance. This landscape is conducive to convergence. In (B), the adaptive landscape is viewed as being like rolling hills, with many alternative routes to nearby adaptive hilltops that are not substantially different from one another. With so many alternative paths and alternative similar hilltops, under this scenario sequences would be unlikely to converge (i.e., follow the same path) even under similar adaptive pressure.

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