Recently we have been reporting on the negative ramifications that testosterone appears to have on various aspects of male behavior such as stock-trading, war-making and promiscuity. A study released in the November 21st edition of Science shows that it’s not just males that are up to no good! Female promiscuity encourages “sperm cocktails” which may lead to competition among the “swimmers”. But, could other evolutionary pressures be involved in having multiple male partners, also known as polyandry?
The new research shows that it may be that males are also driving their partners to infidelity,at least on an evolutionary time-scale, and as it applies to fruit flies. The evidence shows that male “selfish” sperm may selectively attack XY sperm to select for female progeny, and, it appears, the female’s defense to that “attack” is to seek multiple partners.
Science Online reports:
“Selfish” genes break the 50-50 inheritance rule by being passed onto offspring more often than not. Selfish genes “fight” other genes to get passed on to the next generation, often harming the carrier by causing problems such as reduced fertility. For example, male fruit flies can carry a selfish gene that destroys all of their sperm with a Y chromosome, so they produce fewer sperm and can father only daughters. Yet, male fruit flies with the selfish gene are physically identical to those without it.
To test whether females might evolve polyandry in response to the gene, the researchers ran an evolutionary experiment. They compared mating behavior between four fruit fly lines in which the selfish gene was present in about 30% of the males, and eight fruit fly lines lacking the gene entirely. Females in all the fruit fly lines showed nearly identical mating rates at the outset of the experiment. But after 10 generations, females from the selfish gene population remated, on average, almost a full day sooner than females from the populations without the selfish gene, the researchers report today in Science (p. 1241).
Remating increased the females’ chances of snagging a male fly with normal fertility, the researchers note. The findings present a new explanation for polyandry: that it represents an attempt to prevent the spread of selfish genes, Wedell says. “I suspect this may be more general [than just flies] simply because selfish genes are ubiquitous.”
Carol Boggs, an evolutionary ecologist at Stanford University in Palo Alto, California, says the work makes an important contribution to our understanding of how mating systems evolve. It’s the first study to look at the potential impact of selfish genes on mating systems, she says. “This is something that could very well be a factor in the determining the evolution of polyandry.”
We’ll have to wait until Judge Judy rules on the science, but it certainly looks like the blame for infidelity in both sexes is being squarely placed on the male!
Science Online: Why the Lady is a Tramp