The ancestors of rattlesnakes had — and then lost — key genes involved in producing prey-paralysing venom.
The venom of North American diamondback rattlesnakes (Crotalus atrox, pictured, and C. adamanteus) targets the muscles and blood of victims, whereas the venom of the closely related Mojave rattlesnake (C. scutulatus) attacks the nervous system. To determine how these venoms evolved, a team led by Noah Dowell and Sean Carroll at the University of Wisconsin–Madison analysed the genomes of the three rattlesnakes and more distantly related snakes. Comparisons of venom genes suggest that the last common ancestor of rattlesnakes, which lived some 22 million years ago, had various toxin genes. The two diamondback lineages then independently lost the neurotoxin genes, and Mojave rattlers lost the genes to make muscle-attacking venom.
Shifting diets that included prey that were more resistant to a particular toxin may explain these losses, the authors say.
Curr. Biol. http://doi.org/bqpn (2016)
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How snakes lost venom genes. Nature 537, 453 (2016). https://doi.org/10.1038/537453c
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DOI: https://doi.org/10.1038/537453c
