Shattering DNA may have let gibbons evolve new species

Gibbons have such strange, scrambled DNA, it looks like someone has taken a hammer to it. Their genome has been massively reshuffled, and some biologists say that could be how new gibbon species evolved.

Gibbons are apes, and were the first to break away from the line that led to humans. There are around 16 living gibbon species, in four genera. They all have small bodies, long arms and no tails. But it's what gibbons don't share that is most unusual. Each species carries a distinct number of chromosomes in its genome: some species have just 38 pairs, some as many as 52 pairs.

"This 'genome plasticity' has always been a mystery," says Wesley Warren of Washington University in St Louis, Missouri. It is almost as if the genome exploded and was then pieced back together in the wrong order.

To understand why, Warren and his colleagues have now produced the first draft of a gibbon genome. It comes from a female northern white-cheeked gibbon (Nomascus leucogenys) called Asia.

Inside the genome, Warren and his colleagues may have identified one of the players responsible for the reshuffling. It is called LAVA, and it is a piece of DNA called a retrotransposon that inserts itself into the genetic code. Seemingly unique to gibbons, LAVA tends to slip into genes that help control the way chromosomes pair up during cell division. By altering how those genes work, LAVA has made the gibbon genome unstable.

"We believe this is the driving force that causes, for want of a better word, the 'scrambling' of the genome," says Warren.

However, solving this mystery has created another. Such dramatic genome changes are normally associated with diseases such as cancer, and should be harmful. "It's a complete mystery still how these genomes are able to pass from one generation to the next and not cause any major issues in terms of survival of the species," says Warren.

It may be that genomes are much more resilient than anyone expected, says James Shapiro at the University of Chicago. "The genome can endure lots of changes and still function."

Shapiro is one of a growing number of researchers convinced that such major reshuffling has been crucial throughout evolutionary history. He says it is how new species form. This challenges the standard idea that mutations in one or a few genes are enough to establish a new species.

Shapiro's controversial idea has a long history. One of its most famous to some, notorious proponents was German geneticist Richard Goldschmidt. In 1940, he called the animals produced by genome reshuffling "hopeful monsters" (Nature Reviews Genetics, DOI: 10.1038/nrg979). They were "monstrous" because they differed hugely from their parents, but they carried the "hope" of founding a new species because of those differences.

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Shattering DNA may have let gibbons evolve new species