Sexual frustration decreases lifespan -- at least in flies
This will change your whole concept of dead sexy: The chemical attractant wafting from a female fruit fly shortened the lifespan of male flies when the femme fatale didn’t deliver on the signal’s promise, according to a new study.
Male fruit flies who pick up on the female pheromone will decrease their fat stores and lose resistance to starvation, according to the study published online Thursday in the journal Science.
The results shed light on the complex and largely hidden ways that perceptions of peers and environment can affect the chemical pathways involved in aging, said Scott D. Pletcher, a molecular physiologist at the University of Michigan, and one of the authors of the study.
The lowly Drosophila melanogaster has proved a worthy model for many neurological functions among humans, including learning, memory, epilepsy, circadian rhythm, even addictive behavior.
Last year, a UC San Francisco team showed that sexually jilted flies will resort to drinking alcohol (fruit flies like alcohol and will become addicted). That behavior was mediated through a brain chemical called neuropeptide F, which helps drive the brain’s reward circuitry and has an equivalent in human brains.
The same brain chemical appears to play a prominent role in the current findings, according to the researchers.
“The brain is receiving information from its surroundings,” Pletcher said. “That information can be powerful, because it can drive these physiological changes from just a small number of neurons.”
The activity of at least 188 genes, in fact, appeared to be affected by exposure to the pheromones, the study found. Several were linked to odor detection, lipid processing, and immune and stress responses.
The researchers were driven to look at sexual stimuli after finding that exposing flies to the odor of food -- without them eating it -- could reverse anti-aging effects of calorie restriction, which has been shown to promote longevity in humans.
“That argued that it’s not the energetic component of the food, but the fly’s interpretation of its food environment that’s important for at least some significant component of the longevity effect,” Pletcher said.
The researchers cast about for another stimulus to test, and opted for sex pheromones. They exposed male fruit flies to the female pheromones via other males whose chemistry was altered to mimic females. That put pheromones on the table, but took copulation off, and it clearly left the guys frustrated.
By letting the male consort with a female, researchers observed a reversal of the age signaling in the fly brain -- a recovery made more prominent when male flies hung out with five females (five times in a row is the magic number before male flies need a bowl of Wheaties).
“So, sex is good for the flies if they’re expecting it, and it’s particularly bad if they’re expecting it and they don’t get it,” Pletcher said.
The results add to a growing body of evidence suggesting that signaling fitness for reproduction can come at a cost, a trade-off apparent across many species. That can cause a feedback loop affecting not just individuals, but a population, a phenomenon that could help clarify how sexual selection drives evolution.
Pletcher and his colleagues showed last year that increased insulin signaling heightened sexual attractiveness in female fruit flies, via mechanisms that involve pheromone production. But it also lowered longevity.
Now, Pletcher’s data suggest that males picking up on the strong pheromone production typical of these attractive females will risk long-term survival for a shot at reproduction.
“What it suggests is that pathways that impact aging in one organism can reach out and modulate aging at a distance, through social interactions,” Pletcher said.
“Flies continue to impress me with their ability to serve as models for unusual things,” he added.
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