It's almost too good to be true. A Thanksgiving story about sex, death, gender conflict and... roundworms. A Stanford study published today in Science Express suggests that, in some species of worms and flies, males secrete compounds specifically to shorten the lifespan of nearby females. As a result, their mere presence initiates an inexorable early death sequence that the researchers call "male-induced demise."
(Let's all pause here for a deeply satisfying comparison to certain relationships in our own lives...)
The researchers, including Stanford geneticist and longevity expert Anne Brunet, PhD, and postdoctoral scholar Travis Maures, PhD, studied the laboratory roundworm, C. elegans, which has hermaphrodites rather than true females. Their research indicates that male roundworms secrete as-yet-unidentified molecules that act on hermaphrodites sequestered on the other side of a laboratory dish, or those added to a laboratory dish from which a batch of males had recently been evicted. Those hermaphrodites have a lifespan more than 20 percent shorter than controls not exposed to males.
The finding appears to counteract previous theories suggesting that the act of mating (which in worms can be - shall we say - quite rowdy) is responsible for the hermaphrodites' early demise. As I wrote in our press release:
For several years, it’s been known that the presence of some male worms and flies can shorten the lifespan of their female or hermaphroditic counterparts. But it’s not been clear why. Some researchers have speculated that the physical stress of mating may lead to their early death.
The Stanford research, however, suggests something more than sex is to blame — specifically, that the males are carrying out a calculated plan at the molecular level to off the baby-makers after they’ve done their jobs.
The motive? Brunet and Maures speculate the murderous spree could be triggered by a need to conserve resources for newly produced young, or to prevent other males from mating with the same female. From the release:
“In worms, once the male has mated and eggs are produced, the hermaphrodite mother can be discarded,” Brunet said. “The C. elegans mother is not needed to care for the baby worms. Why should it be allowed to stay around and eat? Also, if she dies, no other male can get to her and thus introduce his genes into the gene pool.”
The researchers found that the continuous presence of young males shortened the average lifespan of C. elegans hermaphrodites by more than 20 percent. This effect persisted even when the genders were prevented from co-mingling, or when the hermaphrodites were sterile — indicating that neither the physical stress of copulation nor the energy demands of producing offspring were entirely responsible for early death. Affected hermaphrodites also displayed symptoms of aging, including slower movement, an increased incidence of paralysis, general decrepitude and structural decline.
It's almost unbearably tempting to extend these findings to mammals or even humans.The presence of males leads to general decrepitude and structural decline in nearby females? I'll go with it. And they exert this lifespan shortening effect over both space and time? Check. (In my house this is accomplished by my husband’s refusal to put his dishes in the dishwasher before leaving the house, but your trigger may vary.)
However, such nefarious tactics are likely to seriously backfire when a mother (or a set of parents) is needed to care for helpless offspring. In that case, males would appear to have little incentive to kill off their partners. Even so, the results indicate that this tactic has been going on for millions of years:
Although the researchers first studied a domesticated strain of C. elegans, they were also able to observe male-induced demise in a wild strain of C. elegans, as well as in two other, distantly related species of worm — confirming that the phenomenon has been conserved over about 20 to 30 million years of evolution. The male-induced demise even occurred in species of roundworm that have true males and true females in an equal mix (similar to mammals), suggesting that this phenomenon is not just due to idiosyncrasies of C. elegans such as hermaphroditism or a low proportion of males.
“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. “It will be interesting, of course, to determine whether males also affect the lifespan of females in other species, particularly mammals.”