Sci. Aging Knowl. Environ., 28 September 2005
Battle of the Sexes
Male bean weevils shape female aging
R. John Davenporthttp://sageke.sciencemag.org/cgi/content/full/2005/39/nf77
A henpecked husband might gripe that his wife's nagging is taking years off his life. But in bean weevils at least, one sex can stretch rather than shorten the other's life span, according to new work. In the beetles, selecting males to delay breeding extends the longevity of females with whom they mate. The study provides new insight into the evolutionary forces that alter aging rates.
Longevity seems like a good thing--at least to most of us. But extra time doesn't always bring added benefits, at least from an evolutionary perspective. A gene that enhances reproductive prowess can persist, even if it hastens death. Organisms often age more quickly when forced to reproduce early, supporting the hypothesis that they invest in procreation or survival, but not both. Researchers want to understand the forces that determine how an organism makes this choice. According to an evolutionary theory known as sexual conflict, traits that increase the fitness of one sex can decrease the fitness of the other sex, leading males and females to continually adapt to each other. Several years ago, evolutionary biologist Daniel Promislow of the University of Georgia, Athens, proposed that this tug of war could influence the rate at which each sex ages. In new work, evolutionary biologist Alexei Maklakov of Uppsala University in Sweden and colleagues tested the hypothesis.
The researchers started with two lines of weevils. One line consisted of individuals selected in the lab to mate early in life; the second contained bugs that were selected to mate later. The team paired males from each group with females from a third lineage that hadn't undergone selection. Females that coupled with males from the "late" group died at a slower rate than did those that mated with early-breeding males. Females bred to males that hadn't been selected to reproduce at a particular time lived an intermediate life span. Next, the team noted the age at which each female laid eggs and assessed how long the offspring from each type of pairing took to reach adulthood. Progeny from early males developed more quickly than did those from late males. Typically, the older the mother, the slower her progeny grow up. This increase in maturation time was more dramatic when females mated with early males than with late males. Together, the findings suggest that males selected to postpone breeding induce longevity in unrelated females, even though the females weren't themselves adapted to those conditions. Maklakov isn't sure how males influence female aging, but researchers know that insect sperm can contain harmful and beneficial molecules. For example, late-breeding males might help females--which don't eat as adults--survive by providing extra nutrients in their sperm, he says.
"Males in all kinds of species have lots of tricks up their sleeves to ensure their reproductive success," says biologist Adam Chippindale of Queens University in Kingston, Ontario, Canada. "This is another example of how males can fine-tune their chemical influence on females," he says. "The question is whether one side effect of [sexual conflict] is to alter rates of aging," says Promislow. "Alex's work suggests the answer is yes." Now, beleaguered spouses can only hope they'll live longer too.
September 28, 2005
Science of Aging Knowledge Environment. ISSN 1539-6150