Mere Presence of Males Shortens Female Worms Lifespan, Giving an Evolutionary Advantage

Answering a long standing question, a new study found that male roundworms secrete signaling molecules that significantly shorten the lifespan of the opposite sex.

For years, researchers have known that the presence of some male worms and flies can shorten the lifespan of their female counterparts. Until now, though, researchers had been unable to explain why or how. While some scientists speculated that physical stress of mating may lead to an early death, the researchers wanted to investigate a bit further.

In this particular study, they took a closer look at the common laboratory roundworm, known as C. elegans. This worm generally lives for about 20 days, and a normal population consists of about .01 to .1 percent males. The remainder consists of hermaphrodites, which have both male and female reproductive organs.

"We've found that males induce the expression of a large number of genes involved in sensation and signaling in hermaphrodites," said Anne Brunet, one of the researchers, in a news release. "This raises the possibility that the male-induced demise is not just due to the physical stress of copulation but instead involves some degree of active signaling. Indeed, we found that just placing hermaphrodites on plates where males had previously been present was sufficient to induce the premature demise of hermaphrodites."

So why would males attempt to kill off females? It's possible that the adaptation could serve to conserve precious resources for a male's offspring. It could also decrease the supply of mates for other males. As tempting as it might be to extend the findings to mammals, though, it would likely backfire in situations where mothers, or parents, are needed to rear the young.

"In worms, once the male has mated and eggs are produced, the hermaphrodite mother can be discarded," said Brunet in a news release. "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 findings reveal a little bit more about this peculiar adaptation among roundworms and other species. More specifically, it shows the adaptive benefits for roundworms of "killing off" the female after she reproduces . Currently, the researchers are planning a look a bit further into this particular adaptation in order to see if it extends to other animals.

The findings are published in the journal Science.