The signaling molecules secreted by roundworm males cut down the lifespan of the opposite sex by more than 20 percent, according to a Stanford University School of Medicine study.

Researchers have always known that the company of some male worms and flies can cause early death of their female or hermaphroditic counterparts. Some of them hypothesized that it is due to the physical stress of mating.

For the study, the researchers examined Caenorhabditis elegans, the common laboratory roundworm that generally lives for about 20 days. On average, about 0.01-0.1 percent of the roundworm population comprises of males, while the remaining include hermaphrodites. The hermaphrodites can self-fertilize but produce more offspring when they mate with a male.

"We've found that males induce the expression of a large number of genes involved in sensation and signaling in hermaphrodites," Anne Brunet, PhD, associate professor of genetics, said in apress 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."

Researchers further said that just by placing the hermaphrodites on plates where males had previously been present was sufficient to cause their early death. The benefit achieved by males out of hermaphrodites' early demise is that they can preserve resources for their offspring and decrease mating options for other males.

"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 study has been published in the journal Science Express.