Male Roundworms Use Pheromones to Harm Mates

Male roundworms secrete hormones that reduce the lifespan of their hermaphrodite mates say researchers at Stanford University School of Medicine.

Laboratory roundworm Caenorhabditis elegans exists either as a male or a hermaphrodite. Researchers found that males express genes encoding diffusible pheromone signals that cause premature aging and death in their mates. Just placing hermaphrodites on plates that males had previously inhabited was enough to induce earlier death, suggesting that males had secreted a harmful substance. Furthermore, continuous cohabitation with young males caused signs of aging such as slower movement and a 20% decrease in life span.

It was previously hypothesised that physical exhaustion caused by mating may adversely affect longevity, but the research found that lifespan decreased even when mating was prevented.  Reproductively sterilised hermaphrodites were affected too, proving that the exertion of reproduction was not a satisfactory explanation either. However, hermaphrodites bred to be insensitive to pheromones were resistant to the early demise. Professor Brunet, leading author of the study, thinks that the effect of the pheromones is exacerbated when a pair actually mates, as they could be secreted directly inside via the seminal fluid. The exact pheromones and their mechanism of causing premature fatality are still unknown.

This homicidal, sexually-dimorphic adaptation could have evolved to reduce local competition from the mother so that the offspring have access to more resources, and/or to decrease the supply of mates for other males. As a roundworm mother does not practice childcare, she is disposable to the male once eggs have been produced, and as Brunet puts it, “…Why should she be allowed to stay around and eat?”

The researchers also found male-induced demise in two other, distantly related worm species, suggesting the trait evolved 20-30 million years ago. It has also been shown in flies, and Brunet is interested to see if a similar mechanism occurs in any mammals.

Read more at: http://med.stanford.edu/ism/2013/november/brunet.html