Sturgeon Are Fastest-evolving Fish on Earth, Study Says

When accounting for the change in body size over time, sturgeon are the fastest-evolving fish on the planet, according to a new study, which presents some evidence contrary to a popular belief that the prehistoric-looking fish have lived unchanged for millions of years.

"Sturgeon are thought of as a living fossil group that has undergone relatively slow rates of anatomical change over time. But that's simply not true," said Daniel Rabosky, an assistant professor of ecology and evolutionary biology at the University of Michigan and lead author of the study.

"Our study shows that sturgeon are evolving very quickly in some ways. They have evolved a huge range of body sizes. There are dwarf sturgeon the size of a bass and several other species that are nearly as big as a Volkswagen."

The study involved creating one of the largest evolutionary trees ever created for any group of animals, outlining the relationships between 8,000 species of fish, when then delineated over all the branches of the evolutionary tree, allows the biologists to make inferences to about 30,000 species of fish. The data set was so large that Rabosky and his team had to develop new computer programs to analyze it.

The conclusions about the sturgeon were just one of the many reached as a result of analyzing the evolutionary tree.

"We're basically validating a lot of ideas that have been out there since Darwin, but which had never been tested at this scale due to lack of data and the limits of existing technologies," Rabosky said in a statement. 

Most of the fish analyzed fall into one of two groups: fish that form species very slowly and show little range in body size, like gar, and fish that form species very rapidly and have a variety of sizes, like fish in the salmon family, which include salmon, trout, whitefish and char.

The sturgeon, however, don't fit neatly into the data set. There are only 29 species of sturgeon known worldwide, but they represent a wide range of body sizes.

"In that sense, they're kind of an outlier," Rabosky said.

Rabosky and his colleagues' work is published in the journal Nature Communications.