"Living Fossils" Sturgeons are Evolving Very Quickly: Researchers Say

Sturgeons or the "living fossils" are actually the fastest-evolving fish on earth, a new study has found.

The prehistoric-looking fish has received a lot of attention in the past few years due to efforts to restore its population in the Great Lakes.

"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, assistant professor in the University of Michigan Department of Ecology and Evolutionary Biology.

Sturgeons have been on earth for about 100 million years and today have about 29 species.

Researchers found that the fish have evolved more rapidly, increasing body size over time.

"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," added Rabosky, according to a news release.

Researchers haven't just shown that the sturgeon are rapidly evolving, but have also assembled one of the largest family trees in the world. They have found relationships between nearly 8,000 species of fish. With this information, researchers can infer data on over 30,000 species of the ray-finned fish. The data for the study was collected from public databases about DNA sequence and body sizes of the fish.

According to Rabosky, the study also tested a theory in evolutionary biology that was essentially based on anecdotal evidence. Some species are described as "living fossils" because although they have existed since prehistoric times, they haven't really changed anatomically. The term "living fossil" was coined by Charles Darwin, and gar (found in Great Lakes) and the lungfish are examples of living fossils.

Now, it is known that animals that have many species have high variation in anatomical features, while animals that have fewer species lack such variation.

In the current study, researchers made a time-calibrated evolutionary family tree for 7,864 fish. A strong co-relation between diversification of species and variation in anatomical features was found among the 30,000 species of ray-finned fish.

"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.

The team found that fish such as gar fall in the type of fish that have few species and have few anatomical variation, and that fish such as salmon have many species and greater body size variation.

The sturgeons don't fit in the model proposed by Rabosky's team as there are few species of the fish, but they have great variation in body size.

The study is published in the journal Nature Communications.