University of Denver Winter 2023

WHEN THE CRICKETS STOP CHIRPING

By Matt Meyer

humans. Alongside the cricket, a non-native fly from North America was introduced, creating an isolated area that is the only place in the world where these two species interact. At first, the Pacific field crickets chirped much like their counterparts in Colorado. But the flies used their song as a beacon to locate male crickets. The fly would then parasitize the cricket, spraying its larvae on the carapace. In the insect equivalent of the chest-bursting scene from the movie “Alien,” those larvae burrowed into the cricket, devouring the insect from the inside out and emerging to pupate and become adult flies. Before long, the cricket population fell silent, but their numbers soon dipped, likely because reproduction—typi cally initiated through chirping—was taking place only when the crickets haphazardly bumped into

Across huge swaths of rural countryside, and perhaps even in your backyard, the chirping of crickets weaves into nature’s songs of the night. But where urban development confronts nature’s splendor, those chirps can be drowned out, affecting the insect’s ability to attract a mate and procreate. While traffic noise is the main culprit, everything from construction to power generation can overpower the voice tiny crickets use to connect with one another. That’s even true in protected areas miles from the nearest big burg. In fact, the National Park Service estimates that 63% of the land it manages has noise levels at least double that of their natural state. Some areas were measured as much as 10 times higher than their natural estimates.

University of Denver professor Robin Tinghitella, an evolutionary biologist with the College of Natural Sciences and Mathematics, has an ear tuned to the voice of crickets—and to the widespread implications of evolutionary pressures placed on them over several generations by the encroachment of humans. Cities and human activities, she says, “are imposing different selective pressures on animals.” Tinghitella and her team use a mixture of field and lab research to study these pressures and how they generate rapid evolutionary changes. Her findings, which have advanced our understanding of evolution and the impact of

one another. However, a few generations later, something remarkable happened. The crickets began to rattle and purr. These new noises increased the ability of the crickets to find one another for copulation, while spar ing them the grisly consequences of serving as a fly factory. Tinghitella says much can be gleaned from that process. Evolu years to play out in humans, but they can do so in the span of mere months or years, as the 90-day lifecycle of a cricket brings one generation after another. How does animal behavior evolve? That tionary pressures might take hundreds—if not thousands—of

question keeps Tinghitella busy. “It’s important,” she says, “because when animals come into contact with each other and don’t encounter each other anywhere else in their range, which is common when human actions bring them together unnaturally, they exert selection on each other. That’s how you get these rapid evolutionary changes, like the crickets with the flies.” The examination of natural and urban environments makes for a collaborative research space. For Tinghitella, a highlight is the number of undergraduate researchers who can make meaningful contributions to the work. “In a lot of universities, there’s one lucky undergrad in each lab,” Tinghitella says. “We’ve got 11 in the lab right now. They’re our partners in crime. They’re out in the field, and they stay up all night with us collecting cool data. It’s a super collaborative situation and something that’s not only extremely valuable to them, but also to us.”

urbanization on wildlife, have implications for anyone concerned about preserving the planet’s biodiversity. “The advantage of being able to watch evolution happen in real time is that we can make predictions about what processes allow organisms to persist when we keep changing their environments,” Tinghitella says. “Are there parts of an animal’s life that are going to more easily adapt to human-induced change? Are there things that are going to be really stubborn, that are really important to their fitness—their ability to survive and reproduce—that just can’t evolve to match the changes that we’re imposing on their environments?” A particularly telling example of evolutionary triggers comes from Tinghitella’s research across multiple islands in Hawaii, where the chirps of crickets disappeared entirely for a time. Hawaii is home to a population of Pacific field crickets, a non-native species from Australia introduced to the state by

WINTER 2023 • UNIVERSITY of DENVER MAGAZINE | 27