Fruit flies choose sex over survival and will mate even when infected with deadly pathogens

Scientists say findings will inform future research into human sex drive, Liam James reports

Drosophila melanogaster, or the common fruit fly, holds many secrets about biology (Getty)

A dying fruit fly will not be swayed from seeking a mate, according to a new study.

Researchers from the University of Birmingham found the insects showed a similar level of interest in sex when infected with a deadly pathogen as when healthy and would favour mating over survival.

For any creature, battling an illness takes up much of the body’s energy, meaning there is less to use on other activities.

So scientists were surprised to find that fruit flies continue to dedicate the same amount of energy to trying to reproduce even when they are infected with a deadly pathogen.

And it cannot be the case that flies are oblivious to disease, as previous studies have shown that infection can affect a fly’s movement, sleep and feeding behaviour.

The latest findings, published in Proceedings of the Royal Society B, add to a fairly large, but widely contrasting, body of research into the sex drives of infected animals.

Dr Carolina Rezaval, leader of the research team at the University of Birmingham, told The Independent: “Several studies have shown that individuals exposed to harmful infections prioritise defence over reproductive strategies.

“For instance, upon infection, some insects and birds show decreased egg production, whereas infected crickets and fish show reduced sperm production and viability.

“Further, time invested in courtship and overall performance is affected in response to infection in birds and fish. On the other hand, studies in several species have indicated increased reproductive effort during infection.

“Which factors that determine the choice between reproduction and defence strategies are poorly understood.”

Fruit flies could prove instrumental in increasing this understanding. The Birmingham Fly Facility (BFF), where the latest study was conducted, has helped scientists time and time again in making fundamental discoveries about nature and biology.

This is because fruit flies, scientifically known as Drosophila melanogaster, are the best known living biological diagram for scientists to use in genetic study. Discoveries from the BFF have won six nobel prizes for their contribution to the understanding of human health and disease.

Although humans and fruit flies may appear worlds apart, it has been established that most of the fundamental biological features that control development and survival have been conserved across the wide evolutionary divergence between these species.

For instance, a recent study on fruit flies suggested humans were likely to choose food over sex after being deprived of both.

The results of the latest study, however, do not mean humans necessarily have the same attitude to sex while infected as fruit flies.

Dr Rezaval said: “There is a huge variability in the way animals prioritise investment strategies upon infection. The trade-off between immunity and reproduction appears to be context-dependent and affected by a multitude of factors, including the genetic background of the host, its internal state, and the nature of the pathogen.”

“More work considering external and internal factors during infection across species will help understand if different animal species share investment strategies.”

In other words, the jury is still out on whether humans would choose sex over health.

The University of Birmingham study can be found here.