Sex, crickets and videotape

Cameras focus on insects singing, mating and fighting in the wild to see whether lab science has gotten it right

View a video of a male cricket’s calling songs

TOGETHERNESS CAUGHT ON CAMERA: An extensive field study of the mating habits of crickets deployed 64 security cameras to capture the goings-on. Here, a male field cricket (left) mates by remote action with a female (right) outside his burrow. He has attached a light brown sperm packet to the end of her abdomen, and while he stands ready to chase away rivals, the packet pulses and delivers sperm. Image courtesy of T. Tregenza and R. Rodríguez-Mu±oz

Thanks to a kind of science reality show, evolutionary biologists are getting a reality check. The day-to-day lives of field crickets, captured on 250,000 hours of surveillance footage, are providing a glimpse into how well studies in the lab match up with life in the wild.

Much of indoor science proved applicable outdoors, but there were surprises, including a more complicated view of how the number of mates relates to the number of offspring, according to the first report on the project, appearing in the June 4 Science.

Biologists have long studied crickets in labs to test ideas about mate choice and other aspects of evolution. To take those questions into the wild, researchers deployed 64 security cameras with motion detectors and infrared sensitivity to monitor flightless field crickets (species Gryllus campestris) day and night in a meadow in northern Spain for the 2006 breeding season. Rolando Rodríguez-Mu±oz of the University of Exeter’s campus in Penryn, England, watched every hour of the take. He managed by viewing video from multiple cameras at the same time and speeding through stretches where nothing relevant happened.

One of the surprises, says study coauthor Tom Tregenza , also at Penryn, was that dominant males, which routinely trounce other males in fights, have relatively modest love lives. Lab studies had shown that females prefer a dominant scent to the whiff of routine losers, and also that dominant males can monopolize females by chasing off rivals. Despite such advantages, the dominant males in the meadow had only about half the number of mates during the breeding season that the routine losers did.

Yet in a further twist, the dominant males apparently compensated for their relatively low number of mating partners and ended up with plentiful surviving offspring. “Just having a lot of mates isn’t the whole story,” Tregenza says.

Researchers also found that males that sang more ended up with more offspring, as expected from lab work, but that relationship held only for smaller males. Large male crickets in the meadow attracted females about equally well regardless of how much the males sang.

Even with all the singing and flirting and fighting, reproduction proved an iffy business. Among 77 females in the meadow, more than 40 left no surviving offspring. Fewer than 10 managed to leave even one.

Just looking at the beginning of the process, plenty of crickets of both sexes failed to mate even once (on camera at least). “For a male, perhaps understandable, but what did these females do wrong?” muses Hanna Kokko, currently a visiting fellow at the Australian National University in Canberra, who was not involved in the study.

One prediction that did prove true in the meadow was the fundamental expectation that males typically vary more than females in the number of offspring they produce. The cricket study provides the first confirmation of this principle in wild invertebrates, Tregenza says.

Animal behaviorist Ann V. Hedrick  of the University of California, Davis, who studies a different cricket species, says that the video project “has provided us with extremely valuable information that really hasn’t been possible to collect before.”

Crickets, fruit flies and other small, easy-to-wrangle invertebrates tend to dominate lab studies of sexual and natural selection. In contrast, bigger animals such as deer and meerkats are the most common subjects of long-term field studies. But “you can’t have a lab full of red deer,” Tregenza says. The new study attempts to bring together the two research traditions.

“Crickets live more interesting lives than meerkats,” Tregenza says, and he would love an invertebrate answer to the actual science reality show Meerkat Manor. There might be something about the eye of the beholder, he admits, but “Meerkats, watch out!”

CRICKETS ON FILM from Science News on Vimeo.

Using 64 infrared-sensitive, motion-detecting video cameras, researchers kept watch over all the cricket burrows in a meadow day and night. The researchers also tagged all adult crickets in the population and recorded the male’s calling songs. The University of Exeter team used the captured footage to study mating, fighting and other behaviors, and then looked at the number of offspring each adult cricket produced. The project was designed to see how natural selection and sexual selection theories developed from experimental studies of crickets in the lab play out in the wild.

Video credit: Video file © Science/AAAS

Susan Milius is the life sciences writer, covering organismal biology and evolution, and has a special passion for plants, fungi and invertebrates. She studied biology and English literature.

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