Evolution helps beetles find new home on the range

Evolutionary adaption is not exactly something one would expect to watch in real-time. Because evolution in humans and many animals can take hundreds or even thousands of generations, researchers need to use a more rapidly evolving species as a model to track changes that might then be applied to more slowly evolving lifeforms.

Through the use of beetles as a model species, a Colorado State University-led research team has found that evolutionary adaption, either by population movement or adaption to existing habitats, can be tracked in as few as six generations. The study, supported by funding from the National Science Foundation, was recently published in the Proceedings of the National Academy of Sciences.

Tribolium castaneum beetles in containers
Tribolium castaneum beetles

Beetles used to model range expansion

Ruth Hufbauer, a professor in CSU’s Department of Bioagricultural Sciences and Pest Management, directed the beetle research in her lab, and found that adaptive evolution can increase the rate of range expansion and more than double population sizes.

The model species, Tribolium castaneum beetles, helped the team tackle a fundamental question in evolutionary biology: Does evolutionary change drive changes in population size and movement?

“These beetles provide a powerful model system in which we can allow evolution to proceed normally, or constrain it, allowing us to evaluate the effects of rapid adaptation on how quickly a population spreads and how large it grows,” said Hufbauer. “We can’t stop evolution in natural populations of sexually reproducing species. It’s just not possible. But in the lab, we can prevent adaptation entirely.”

When a species is introduced to a new range or the environment changes around it, populations may grow, and the species may spread into new locations. Managers and biologists want to understand the factors that govern population size and the rate of range expansion.

Good evidence shows that species adapt to their novel habitats, but it is not clear whether that adaptation occurs gradually, after a species has successfully colonized new locations, or if instead it can occur so rapidly that it acts as an architect – driving range expansion and population growth.

Hufbauer’s team also included Marianna Szucs, a former research scientist at CSU, now an assistant professor in Michigan State University’s Department of Entomology; Megan Vahsen, a former master’s student at CSU, now a Ph.D. student at Notre Dame University; and Brett Melbourne, an associate professor in the Department of Ecology and Evolutionary Biology at the University of Colorado Boulder.

Professor Ruth Hufbauer picture
Professor Ruth Hufbauer

Preventing rapid evolution to measure its strength

In their experiment, the researchers compared normally evolving populations adapting to a new habitat, and spreading from patch to patch, with populations that could not adapt. The beetles were housed in small, clear containers linked together to form linear landscapes to simulate a species expanding into a novel habitat. To prevent adaptation, researchers replaced individual beetles one-for-one each generation with beetles from a large external population, which also minimized drift and inbreeding. This approach maintained demographic processes, while essentially preventing evolution.

Evolution drives range expansion dynamics

“The magnitude of the effect of evolution that we saw astonished even us,” said Hufbauer. “In six generations, evolving populations spread 46 percent faster and grew about 190 percent larger than the populations that couldn’t adapt. So, evolution apparently can facilitate colonization from the very beginning, and doesn’t just occur after the fact.”

Hufbauer says this argues that the adaptation we see in invasive species is thus likely to be critical to determining how far they spread and how numerous they are. For managers and policy makers, this means that even if a biological invader is already present, it could be important to prevent additional introductions, as new individuals might add genetic variation to introduced populations and allow them to invade further and faster.

The study

More information about this project, “Rapid adaptive evolution in novel environments acts as an architect of population range expansion” can be found on the Proceedings of the National Academy of Sciences website.