Promiscuous females and their role in evolution
Males have to make less of an effort to mate with promiscuous female fruit flies, making the quality and
quantity of their semen all the more important in the competition to fertilise the females’ eggs.
This also leads to male flies repeatedly mating with the same female, according to a paper published
in Nature Communications by researchers from Macquarie University, the University of Oxford and the
University of East Anglia, who looked into the eyes of thousands of fruit flies.
Over the last 50 years, biologists have realised that females in most animal species mate with multiple
males during their lifetimes, in contrast to the Victorian-era fairytale of the monogamous female. However
they didn’t know how this behaviour influences how fruit flies and other species evolve.
Department of Biological Sciences’ Juliano Morimoto and colleagues from the UK wanted to test the
theory that increasing female promiscuity would reduce male competition before mating, while increasing
their competition to fertilise the female’s eggs after mating.
To do this, they first genetically manipulated female Drosophila melanogaster fruit flies to increase their
promiscuity.
By deleting a sex peptide receptor, they reduced the time the females weren’t sexually receptive after
mating and therefore led to them mating more frequently.
Hundreds of the more promiscuous females were marked with paint and their interactions with male flies
monitored. The researchers painstakingly counted the thousands of offspring produced and identified
their fathers based on eye colour.
“We found that when females mate promiscuously, male attractiveness is less important,” says Juliano.
“Instead, having a large ejaculate might be what males need to win the war.”
Photo of a promiscuous female fruit fly (Drosophila melanogaster) marked with paint by The Wigby Lab.
Syllabus Reference: Stage 6 Biology Module 4
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