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Fish teeth show how ease of innovation enables rapid evolution

It's not what you do, it's how readily you do it. Rapid evolutionary change might have more to do with how easily a key innovation can be gained or lost rather than with the innovation itself, according to new work by biologists at the University of California, Davis, who studied how teeth in certain fishes evolved in response to food sources and habitats.

Their work was published in .

"This changes the way we think about key innovations," said Nick Peoples, first author of the paper and a graduate student working with Professor Peter Wainwright at the UC Davis Department of Evolution and Ecology.

Wainwright's lab studies the evolution and diversity of fish. The cichlid fishes of Africa's great lakes are a particularly large and diverse group, adapted to a wide variety of habitats and food sources in the lakes. They form new species more readily than any other group of vertebrates.

Adaptations of the teeth and jaws that allow the fish to adapt to a wide range of food sources and habitats are thought to be a factor in their success. Fish, including cichlids, have either "simple" teeth, basically cone-shaped pegs, or "complex" teeth with multiple cusps that can adapt to feed on different prey.

Peoples spent two years examining the teeth of over 30,000 species of fish, including 1,000 species of African cichlids. He used the data to reconstruct when and how often complex teeth evolved, or disappeared, in fishes.

Across all fishes, complex teeth appeared 86 times but are relatively unusual in modern fish, he found. In the African cichlids, they are far more common.

Peoples discovered that it's not just the appearance of complex teeth that makes species accumulate faster. The ability of cichlid lineages to quickly switch between simple and complex teeth (and back) is itself an innovation that drives the rapid formation of new species.

"It's not just the teeth, it's how quickly they are gained or lost," Peoples said. The African cichlids appear to have retained the genetic program needed to make either type of teeth, meaning that they can evolve to switch between them quite easily.

The discovery that how easily a trait can be gained or lost can itself be an innovation that enables rapid evolution could apply to other innovations that appear multiple times, such as adhesive toe pads for climbing, Peoples said.

Additional authors on the paper are Michalis Mihalitsis at UC Davis and Michael Burns, now at Oregon State University.