Why Males Die Before Females: Competition for Sex

Why do males die earlier than females? That's a good question, and it's one that scientists have explored in fruit flies. The researchers found that male flies die earlier than females when they're forced to evolve with the pressures of mate competition and juvenile survival.

The fruit fly in question is Drosophila simulans. The males of this species court females by "singing," dancing and emitting a scent. However, their efforts come at a considerable cost, and this cost is amplified when additional stressors are added.

Some species, like the flies in this study, age quickly over another of days. Other species, though, such as trees and whales, age slowly across centuries.

"We found dramatic differences in the effects of sexual and natural selection on male and female flies," said David Hosken, one of the researchers, in a news release. "These results could help explain the sex differences in lifespan seen in many species, including humans, and the diverse patterns of aging we observe in nature."

The researchers subjected the flies to elevated or relaxed sexual and natural selection. Then, they left the flies to evolve in these conditions. The sexual selection was elevated by housing males with single females and natural selection was elevated by raising temperatures.

So what did they find? Under relaxed sexual and natural selection, male and female flies had very similar lifespans-around 35 days. Yet the males that evolved under elevated sexual selection and elevated natural selection had a lifespan of just 24 days and, on average, died seven days earlier than females under the same conditions.

The findings reveal how the pressures of mating and natural selection can affect lifespan. More specifically, it shows how these pressures more drastically impact males. This, in turn, shows that the sexes can respond differently to the same selection regimes.

The findings are published in the journal Functional Ecology.

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