July 17, 2008 -- The wisdom of feeding meat to a man has been thrown into question by a study that shows the secret to a long reproductive life in males -- at least among insects -- is not protein, but carbohydrates.
The study, published today in Current Biology, suggests that it is females who should be pulling out the steak knife to ensure their reproductive fitness.
Lead author and University of New South Wales biologist Alexei Maklakov said his study on Australian black field crickets is the first of its kind to examine the influence of gender in determining which diet is best for long life and breeding success.
Although he found that what's good for the goose isn't necessarily good for the gander, males and females end up eating a compromise diet that is less than optimal for both of them.
For the study, which also involved researchers from the University of Sydney and Massey University in New Zealand, the male and female crickets were fed a range of diets that included different ratios of proteins to carbohydrates.
The researchers then studied the insects' response to the diets in terms of lifespan and reproductive fitness.
For the females this meant once a week counting the number of eggs they laid, and for the males, measuring the number of calling noises they made during the night.
The sexes had very different peaks in respect to reproductive fitness and lifespan under different dietary regimes.
Maklakov, from the Evolution and Ecology Research Center, said reproductive success in female crickets is optimized by a diet with a one-to-one ratio of protein to carbohydrates.
For males, however, reproductive success came with a diet favoring carbohydrates over proteins in an eight-to-one ratio.
Male crickets maximize their reproductive success by calling out to prospective mates throughout the night.
"Males don't need much protein," he said. "They just need energy to basically sit and call out all night."
The researchers then studied what the crickets would eat when given a choice in diet. Instead of selecting food in a sex-specific manner, males and females ate a "compromise" diet that benefited neither sex.
"It is rather surprising because they are not doing what they are supposed to do," Maklakov said. "In crickets, males and females do not seem to be able to fully resolve the sexual conflict over what to eat."
For the females the compromise is costly, resulting in a 30 percent reduction in egg production, he said.
The researchers believe the compromise is due to the failure of some gender-dependent traits to evolve. The sexes share most of their genes, which constrains the evolution of sex differences since the same genes in both sexes are likely to be responsible for a given trait.
Rob Brooks, director of the Evolution and Ecology Research Center and a co-author of the study, said the results show more attention needs to be given to individual diets in terms of their sex and reproductive stage.
"It underlines the important lesson that what we want to eat, or if you like, are programmed to eat, is not necessarily best for us," Brook said.
Although humans and crickets are completely different organisms, the study does have ramifications for people, added Brooks.
"It's the first time this kind of [gender difference in diet] has been shown," he said.
"Humans are even more fundamentally different between males and females than crickets are, he added. "In human reproduction the men's role is relatively trivial [while] for women bringing a baby safely to term requires tremendous amounts of energy, and diet is very important.
"What men and women need to eat might be more dramatically different than we had realized," he said. "However, men and women eat very similar diets, and our results suggest our tastes and food preferences could be a shared compromise as they are in crickets."
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