Why females live longer than males

Researchers from the University of Exeter in Britain found that male flies die earlier than their female counterparts when forced to evolve with the pressures of mating and juvenile survival.

The results could help researchers understand the mechanisms involved in ageing.

"We found dramatic differences in the effects of sexual and natural selection on male and female flies. These results could help explain the sex differences in lifespan seen in many species, including humans, and the diverse patterns of ageing we observe in nature," said lead researcher professor David Hosken.

The team used populations of the fly Drosophila simulans that had evolved under different selection regimes.

The flies were then subjected to elevated and relaxed conditions of sexual and natural selection.

To elevate sexual selection, groups of males were housed with single females. A stressful temperature was used to elevate natural selection.

The study shows that mate competition (sexual selection), along with survival (natural selection), is tougher on males than it is on females, reducing their lifespan by about a third.

"Males court females by singing, dancing and smelling good but their efforts come at considerable cost and this cost is amplified when they also have to cope with stressful temperatures," Hosken added.

The results showed that under relaxed sexual and natural selection, male and female flies had very similar life spans - around 35 days.

However males that evolved under elevated sexual selection and elevated natural selection had a much shorter life span - just 24 days.