Exploring Evolution by Studying Beetles Living on the Edge



​Sonoma State professor Nathan Rank and Santa Clara University professor Elizabeth Dahlhoff, along with their collaborators and students, explore the evolutionary responses to environmental challenges by studying a beetle that lives two miles above sea level in the mountains of eastern California. That beetle, according to Dr. Rank, allows them to “study how natural populations of a native California insect cope with environmental stress in a region that is experiencing significant effects of changes in climate.”

The researchers have identified in willow leaf beetles genes help the insects to process energy and cope with temperature stress. These genes “help them to survive and reproduce in a region with long winters and where annual fluctuations in rain, snow, and average temperature are high,” Dr. Rank explained. “These findings are evidence that evolution is going on right before our eyes in a complex organism, not some single-celled bacterium in a petri dish. The implications here for scientific understanding of evolution and adaptation to climate change are profound.”

Rank and Dahlhoff have methodically investigated the willow beetle for decades. He said: “Our most recent work shows that genes on the mitochondrion interact with genes from the nucleus to influence responses to environmental stress. It also appears that responses to low oxygen (hypoxia) interact with responses to stressful temperature to influence beetle populations in the wild. This has been a real surprise because, until now, most physiologists did not think a small insect would even be limited by low oxygen. Turns out, beetles are similar to humans in this respect—they can run out of breath at high elevation. Our current work aims to understand how populations survive both summer and winter thermal stress and environmental variation.” They plan to investigate environmental stress factors on the beetle during severe winters, to look at how cold and energy stressors interact to shape the beetle’s physiological performance during winter and the subsequent growing season. These studies are being conducted with Professor Caroline Williams at UC Berkeley, who is an expert on adaptation to winter in insects.

“We will complete our work on interacting stresses of temperature and oxygen supply on physiological and evolutionary responses to a changing environment,” Rank said. The team’s work on winter survival and responses to stress will be invaluable for studying environmental effects on population persistence. In other words, how does a population adapt and survive—and evolve—in the face of severe changes in climate? A beetle surviving at the limits of its environmental tolerance may offer us clues for how we can overcome challenges posed by the future climate.