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Lady flies decide who will father their babies based on male mating effort

india Updated: Apr 13, 2013 17:58 IST


Females of Euxesta bilimeki, a species of Ulidiid fly, adopt a unique behavior that probably helps them bias male paternity – they expel and then consume male ejaculate after copulation.

Christian Rodriguez-Enriquez and his colleagues from the Instituto de Ecologia in Mexico have been researching the possible reasons why the female of this species might adopt this behavior.

Out of the 74 pairs of flies that engaged in copulation in this study, 100 percent of females expelled the ejaculate. The researchers therefore contend that this behavior is probably just a component of the mating ritual of this species.

Further investigation found that a quarter of females did not retain any sperm after this expulsion. This would further suggest that it helps the females bias paternity as they seem to be able to choose whether to expel all the ejaculate or just some of it.

Interestingly, a long courtship before copulation seemed to increase the likelihood of expulsion of all the ejaculate.

The researchers propose that perhaps the female fly ‘gives in’ after a long courtship to avoid continuously having to reject the male advances but then expels all the ejaculate to prevent that particular fly fathering its young.

It is possible that females consume ejaculate for its nutrients when there are few available food sources. To assess whether this was the case, the researchers took female Euxesta bilimeki flies and fed them either a diet of protein, sugar and water or just sugar and water, just water or nothing at all. These females were then placed either with males who could ejaculate or with males who no longer had the ability to ejaculate.

Thus they could identify whether being well-fed or starved affected the likelihood of consuming ejaculate and also whether it had any positive health benefits.

There did not seem to be any marked benefit to flies, which were fed and watered in consuming the ejaculate. However, flies that were starved of even water lived longer if they consumed the ejaculate than those who were not allowed to consume it.

The researchers suggest that this may be because they are extracting fluids from the ejaculates. Given that this species of fly lives in arid areas, this is one possible evolutionary explanation.

“Overall our study appears to have raised more questions than provided answers. However, we believe that we have uncovered a fascinating study system that will require substantial experimental attention before allowing formulation of conclusive statements about the function of sperm expulsion and consumption in E. bilimeki,” the researchers concluded.

Their study has been published in the Springer journal Behavioral Ecology and Sociobiology.