Restriction and recruitment-gene duplication and the origin and evolution of snake venom toxins.
Bottom Line: Our comparative transcriptomic analysis of these data reveals that snake venom does not evolve through the hypothesized process of duplication and recruitment of genes encoding body proteins.Thus, snake venom evolves through the duplication and subfunctionalization of genes encoding existing salivary proteins.These results highlight the danger of the elegant and intuitive "just-so story" in evolutionary biology.
Affiliation: School of Biological Sciences, Bangor University, United Kingdom.Show MeSH
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Mentions: We find the hypothesis that snake venom evolves through the duplication of physiological or body genes and subsequent recruitment into the venom gland to be unsupported by the available data. In short, snake venom has not evolved through the recruitment of “body” genes. Indeed for a large number of the gene families claimed to have undergone recruitment we find evidence of a diverse tissue expression pattern, including the salivary gland of nonvenomous reptiles (fig. 2), demonstrating that if they do encode toxic venom components (Hargreaves et al. submitted), they have not been recruited into the venom gland, but restricted to it. The recently published king cobra genome paper (Vonk et al. 2013) also provides evidence for salivary (rictal) gland expression of several venom toxins in the Burmese python, Python molurus bivittatus, including 3ftx, cystatin, hyaluronidase, and SVMP (supplementary table S2 in Vonk et al. 2013).Fig. 2.—
Affiliation: School of Biological Sciences, Bangor University, United Kingdom.