15 June 2016

Sex, diet and fruit flies

by Ju Morimoto

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Finding a partner is hard work. When faced with varied mates, we usually consider a range of traits: beauty, personality, wealth, aspirations, kindness, the list goes on. However, few of us would add our partners’ dietary habits to this judgment. But it turns out that, if you are a female fruit fly, you may need to rethink your “perfect partner” criteria and re-prioritize your partner’s diet.

In a recent study published in the journal Scientific Reports, my colleague Stuart Wigby and I showed the negative effects of male diet on female reproduction in fruit flies Drosophila melanogaster. We fed males a variety of diets with different proportions of protein and sugar for four days before males were allowed to mate with virgin females. After mating them for the first time with these males, females were allowed to produce offspring for a day. Next, these same females were mated for a second time with healthy males raised on normal food. After mating with the second males, females were allowed to produce offspring for another three days. Female fruit flies can produce more than 150 offspring in a day and, therefore, four days of offspring production (one day after the first mating + three after the second mating) is a reasonable period of time for assessing female reproduction.

The results are surprising. We found that the diet of the male that copulated with a virgin female can have long-lasting effects on female reproduction. Males that have eaten high protein foods reduced the production of offspring of females over the four days of the experiment even after females had mated again with the healthy male.

Somehow, the diet of female’s first male defines her potential to produce offspring.

But what does this effect mean? It is too early to tell since this is the first study to show this effect. However, we believe that the answer lies in the ejaculate of males. The ejaculate is a cocktail of sperm, sugar, vitamins, proteins and other molecules, and the ejaculates of the majority of species are, to a greater or lesser extent, made of these components. Thus, our results raise the potential for the effects of male diet on female reproduction to be observed elsewhere in animal kingdom, including in humans.

Of course, it is too soon to jump to such conclusions. But if confirmed in humans, these results would suggest that women should choose their first partner not by attractiveness or personality, but perhaps by the number fast food meals her potential partner has eaten lately.

While the list of criteria for finding the perfect match may have just gotten longer, one thing is certain: Choosing the right partner is a very tedious task.

 

Juliano Morimoto is a Brazilian PhD student at the University of Oxford.