NEW SCIENTIST (London, UK) 02 December 13 Snakes outpacing other vertebrates in race to evolve (Bob Holmes)

It seems the slitherers got off to a fast start. The first two full snake genomes to be sequenced – belonging to the Burmese python and the king cobra – show that they have one of the fastest rates of genetic evolution among vertebrates.

Snakes' shape and penchant for infrequent, huge meals suggest they must have undergone a lot of evolutionary change since they diverged from other vertebrates. They also undergo enormous metabolic swings when they eat, activating thousands of genes after a meal and then shutting them down again to allow their internal organs to shrink during fasting periods.

"They've had to make so many changes to adapt to life as a tube," says David Pollock, a geneticist at the University of Colorado at Denver.

When Pollock's team compared nearly 7500 genes from the Burmese python and the king cobra with their counterparts in other vertebrates, they found that the snakes' versions had an unusually high number of evolutionary changes, rivalling the mouse as the highest seen for any vertebrate. "That is extremely impressive, and a surprise even to us," says Todd Castoe of the University of Texas at Arlington, another member of the team.

Of the genes undergoing the strongest evolutionary change, many are involved in body shape and organ development, metabolism, venom production and the sense of smell.

Many of those changes were in the parts of the genes that code for proteins, rather than in the regulatory sequences that turn genes on and off. This runs counter to a long-held theory that most evolutionary change happens by altering not genes themselves but when they become active.

Pollock says that snakes' genomes may be unusually prone to change because they contain many repeated sequences that promote misalignment of chromosomes and so make gene duplications more common. Many of the cobra's venom genes, for example, seem to have arisen from duplications of genes that control secretions from the pancreas, the team found.

This evolutionary nimbleness may make snakes more able to adapt to future challenges too, says Scott Edwards, an evolutionary biologist at Harvard. However, he adds, snakes' "fast" evolutionary changes still took millions of years to accumulate. "Whether they're labile enough to resist all the challenges of habitat loss and climate change is unclear," he says. "It's a different timescale."

Journal reference: PNAS, DOI: 10.1073/pnas.1314475110
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