The mighty tuna is more closely related to the delicate seahorse than to a marlin or sailfish. That is one of the surprises from the first comprehensive family tree, or phylogeny, of the "spiny-rayed fish," a group that includes about a third of all living vertebrate species. The work is published July 15 in the journal Proceedings of the National Academy of Sciences.
The spiny-rayed fish are an incredibly diverse group, including tuna and billfish, tiny gobies and seahorses, and oddities such as pufferfish and anglerfish. The fish occupy every aquatic environment from coral reefs and open oceans to lakes and ponds. It includes all the major commercially fished species -- all of which are threatened. But until now, no one has had any idea exactly how more than 18,000 species in 650 families are related to each other, said Peter Wainwright, professor and chair of evolution and ecology at the University of California, Davis and senior author on the paper.
"There has been a 'bush' at the top of the family tree leading to the rest of the vertebrates," Wainwright said. "Now we have this beautiful phylogeny of one-third of all vertebrates."
The study also shows that after roaring along for their first 100 million years, the pace of evolution of the spiny-rayed fish downshifted about 50 million years ago.
Some groups of fish have gone along steadily for millennia; others have gone through bursts of rapid evolution. Overall, the researchers found that the rate at which new species formed was fairly constant across the group from their origin to about 50 million years ago, then dropped about five-fold and has remained at that level since.
That might mean that these fish have essentially filled the available spaces, Wainwright said.
"It's not uncommon in evolution to see a rapid diversification followed by a slowdown, but it's never been seen on such a scale before," he said.
|Contact: Andy Fell|
University of California - Davis