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Rattlesnakes have reduced their repertoire of venoms

Reptiles’ common ancestor possessed greater variety of toxic proteins

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12:00pm, September 15, 2016
diamondback rattlesnake

STILL A FRIGHTFUL BITE  The venom of the western diamondback rattlesnake (shown here) isn’t neurotoxic — but its ancestor’s was. A loss of genes 4 million to 7 million years ago narrowed the range of toxins this and some other rattlers can use to kill prey. 

Modern rattlesnakes have pared down their weaponry stockpile from their ancestor’s massive arsenal. Today’s rattlers have irreversibly lost entire toxin-producing genes over the course of evolution, narrowing the range of toxins in their venom, scientists report September 15 in Current Biology.

“After going through all the work of evolving powerful toxins, over time, some snakes have dispensed with them,” says study coauthor Sean B. Carroll, an investigator with the Howard Hughes Medical Institute who is at the University of Wisconsin–Madison. These modern rattlesnakes produce smaller sets of toxins that might be more specialized to their prey.

Carroll, an evolutionary biologist, and his colleagues focused on a family of enzymes called phospholipase A2, or PLA2. Genes in the PLA2 family are one of the main sources of toxic proteins in the deadly

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