Scientists decode genome of 'living fossil' fish

Scientists have sequenced the genome of the African coelacanth, an ancient-looking fish with lobed fins, and found that its appearance has changed little over 300 million years as its genes are evolving very slowly.
A sea-cave dwelling, five-foot long fish with limb-like fins, the coelacanth was once thought to be extinct. A living coelacanth was discovered off the African coast in 1938.
Since then, questions about these ancient-looking fish - popularly known as 'living fossils' - have loomed large. Coelacanths today closely resemble the fossilised skeletons of their more than 300-million-year-old ancestors.
Its genome confirms what many researchers had long suspected: genes in coelacanths are evolving more slowly than in other organisms.

"We found that the genes overall are evolving significantly slower than in every other fish and land vertebrate that we looked at," said Jessica Alfoldi, a research scientist at the Broad Institute of MIT and Harvard and co-first author of the paper in journal Nature.
"This is the first time that we've had a big enough gene set to really see that," Alfoldi said.

Researchers hypothesise that this slow rate of change may be because coelacanths simply have not needed to change: they live primarily off of the Eastern African coast (a second coelacanth species lives off the coast of Indonesia), at ocean depths where relatively little has changed over the millennia.

"We often talk about how species have changed over time," said Kerstin Lindblad-Toh, scientific director of the Broad Institute's vertebrate genome biology group and senior author.
"But there are still a few places on Earth where organisms don't have to change, and this is one of them. Coelacanths are likely very specialised to such a specific, non-changing, extreme environment - it is ideally suited to the deep sea just the way it is," Lindblad-Toh said.
Because of their resemblance to fossils dating back millions of years, coelacanths today are often referred to as 'living fossils' - a term coined by Charles Darwin.

But the coelacanth is not a relic of the past brought back to life: it is a species that has survived, reproduced, but changed very little in appearance for millions of years.
"It's not a living fossil; it's a living organism. It doesn't live in a time bubble; it lives in our world, which is why it's so fascinating to find out that its genes are evolving more slowly than ours," said Alfoldi.