Probing the limits of “evolutionary rescue”

Abstract

Could species threatened by climate change and other stresses avoid extinction through rapid evolution? In the space of five years, the field crickets of Kauai fell silent. The quiet was deafening to evolutionary biologist Marlene Zuk, who had spent a decade crawling through Hawaii's vacant lots and church lawns, collecting the insects for her research at the University of California, Riverside. When she started her work, Zuk remembered males as always chirping. But beginning in the 1990s, she saw and heard fewer crickets. It seemed Kauai’s population had careened off an ecological cliff toward extinction. “Evolutionary rescue” may effectively bring back some species from the brink of extinction. There’s evidence that evolution can, at times, be surprisingly fast, as in the case of this cricket and fly interaction on Kauai, HI. Image credit: Norman Lee (St. Olaf College, Northfield, MN). One obvious culprit, Zuk thought, was a small parasitoid fly with remarkable hearing (1). Female flies use their fine-tuned ears to locate a male cricket chirping in the grass and drop their larvae onto his back. The maggots burrow through his carapace and eat his soft insides, bursting out to pupate in the soil about a week later. The drama of the cricket and the fly unfolded nightly in the front yards and hotel lawns of Hawaiian paradise, forcing a big trade-off for male crickets: sing for sex and court a gruesome death. By the early 2000s, Zuk had all but stopped hearing field crickets on Kauai. The roadsides she frequented to collect insects no longer thrummed with the distinctive, nails-along-a-comb chirping of the males. One night in 2003, she opened her car door to silence on her field site. “I thought ‘that's that, but you may as well get out of the car’,” Zuk remembers. She stepped out, clicked …