U-M HEALTH SYSTEMHermaphroditic worms and male flies exposed to the presence of potential sexual partners show signs of aging and die sooner than animals who aren't subjected to others' scents. Sex, however, can rescue the untoward effects of pheromones among the flies, scientists have found. “The simplest way to think about it is that the flies are frustrated,” Scott Pletcher, a University of Michigan researcher and the senior author of the study, published last week (November 29) in Science, told ScienceNow.
Pletcher and his colleagues had found that genetically engineering male fruit flies to produce female pheromones made other male fruit flies waste away and die sooner. But when those males were able to copulate after detecting the pheromones, their lifespans were not affected. In a press release, Pletcher said that “it may not be a myth that sexual frustration is a health issue. Expecting sex without any sexual reward was detrimental to [the flies’] health and cut their lives short.”
In another study on the worm C. elegans, scientists found that placing hermaphroditic worms on a dish that had either currently or previously housed male worms caused the “premature demise” of the hermaphrodites. The research group, led by Anne Brunet of Stanford University, also found a way to rescue the animals. Males that don't produce pheromones or hermaphrodites that can't sense the chemicals are resistant to the longevity-shrinking effects of males' presence.
It's not entirely clear why the opposite sex has such ill effects on health and lifespan. Pletcher told National Geographic’s Not Exactly Rocket Science that expectations—based on the detection of pheromones—might gear up the flies for sex. “They make this bet that they’re going to be reproducing soon, and they engage some physiological changes, like producing hormones,” he said. And when that expectation isn't fulfilled, it takes a toll on the fly.
Brunet's idea, as explained to Not Exactly Rocket Science, is that taking out mating partners ensures less competition for one's offspring. However, she added, “this is wild speculation.”
“The observation that this male-induced demise is present in several species of worms and has also been shown in flies suggests that it could have some adaptive benefits,” Brunet said in a press release. “It will be interesting, of course, to determine whether males also affect the lifespan of females in other species, particularly mammals.”