Is it true that what is good for the goose is good for the gander? Not in all ways.

Intralocus sexual conflict reduces the benefits of sexual selection by diminishing the fitness of offspring produced by the most attractive mates, researchers report in PLoS Biology this week. The study is the first to measure the inheritance of genetic quality from both parents across generations.

When individuals of the same species carry sexually antagonistic genes -- genes that have opposite effects on fitness when expressed in the two sexes -- sexual conflict ensues. "In promiscuous mating systems, many genes that make a good male don't make a good female, . .

The results showed that any potential genetic benefits of sexual selection were reversed in the next generation: high-fitness males produced low-fitness daughters, and high-fitness females produced low-fitness sons. "A male may be high-quality because he has a lot of masculinizing male-benefit genes," explained Pischedda, the first author of the paper. "When a female mates with such a male, those masculinizing genes pass to the offspring, and if they end up in a daughter, they will reduce her fitness. The same thing happens with maternal fitness."

Another result was that males of either high- or low-quality were not able to influence the fitness of their sons in any way. "We think that this is because the majority of sexually antagonistic genes are on the X chromosome," Pischedda said.

They used reproductive success as the measure of fitness.

Fitness was measured as paternity success for males and egg production for females.

There are some interesting implications.

if selection favors the fittest, why is there such a wide degree of genetic diversity in populations? "We believe that intralocus sexual conflict could provide an explanation: selection for high-quality females in a population may oppose selection for high-quality males, and vice versa. This constraint on selection likely helps maintain diversity,"