Will global warming eclipse evolution?

UC DAVIS (US) — Climate change is leaving animals and plants little wiggle room, pushing them to the edge of their heat tolerance level.

A new study, published in the journal Proceedings of the Royal Society B, tracks the struggle for survival of the tiny tide pool copepod, Tigriopus californicus, that has shown little ability to evolve tolerance to increased heat.

The shrimplike animals are about a millimeter long and live in tide pools on rocky outcrops high in the splash zone from Alaska to Baja California.

“This is a question a lot of scientists have been talking about,” says Eric Sanford, associate professor of evolution and ecology at the University of California, Davis. “Do organisms have the ability to adapt to climate change on a timescale of decades?”

Graduate student Morgan Kelly, the first author of the paper, collected copepods from eight locations between Oregon and Baja California and grew them in the lab for 10 generations, subjecting them to increased heat stress to select for more heat-tolerant animals.

At the outset, copepods from different locations showed wide variability in heat tolerance. But within those populations, Kelly was able to coax only about a half-degree Celsius (about one degree Fahrenheit) of increased heat tolerance over 10 generations. In  most groups, the increase in heat tolerance had hit a plateau before that point.

In the wild, copepods can withstand a temperature swing of 20 degrees Celsius a day.

Although copepods are widespread geographically, individual populations are very isolated, confined to a single rocky outcrop where wave splash can carry them between pools—meaning there is very little flow of new genes across the population as a whole.

“It’s been assumed that widespread species have a lot of genetic capacity to work with, but this study shows that may not be so,” says Rick Grosberg, professor of evolution and ecology.

Many other species of animals, birds and plants face stress from climate change, and their habitats have also been fragmented by human activity—perhaps more than we realize, he says.

“The critical point is that many organisms are already at their environmental limits, and natural selection won’t necessarily rescue them.”

The study was funded by the National Science Foundation.

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