Female flies dance of deceit

Wednesday 27 August 2003

Scientists have studied female flies who ‘trick’ males into mating them by changing their appearance to make them appear more fertile.

The trick not only attracts a mate, but promises the added bonus of a ‘nuptial gift’ from her mate – another fly or insect which she devours at the same time as mating.

Led by Dr Natasha LeBas at the University of St Andrews, a team have studied dance flies which ‘ornament’ themselves by holding feather-like ‘frilled’ legs around their abdomens to appear as though they have large abdomens full of eggs. This has been thought to fool males into believing the females have mature eggs ready for fertilisation and that the males will sire their offspring.

In this form of display, the female Empipid dance fly reverses the trend throughout the animal kingdom in which males tend to use elaborate physical and colourful displays (ornaments) to show off and attract female mates.

Dr LeBas, of the University’s School of Biology, said:

“Throughout the animal kingdom there are showy, ornamented males and drab, inconspicuous females. Female ornamentation has long been overlooked because of the greater prevalence of elaborate displays in males.”

The display stems from her desire to attract ‘nuptial gifts’, which are often nutritious sperm bundles, but in this case are different species of flies or insects which the males catch and hold with their legs until they find a suitable female. Males offer such gifts to the most ornamented females.

Females don’t normally invest in such displays unless there are direct benefits (such as nutritional value), so the researchers believe that it is a deliberate ploy of the female to invest in ornamentation in order to receive the gift of nutritious prey. Many female dance flies have lost the ability to hunt, and it has been suggested that they use this display to obtain food.

Dr LeBas explained:

“Females are not expected to invest in ornamentation unless the fitness benefits of the ornament exceed those derived from investing the resources directly into offspring. The circumstances under which females would benefit from honestly signalling their quality are limited however. It has been proposed that when females gain direct benefits from mating, they may instead deceive males about their reproductive state with such ornamentation.”

The team investigated sexual selection and ‘honesty’ in female ornamentation in female dance flies and whether such ornaments deceived males.

However they found that males weren’t always losing out, since females with ornamented legs tended to be more fecund.

“Mated females had a larger total number and more mature eggs than unmated females, highlighting a potential benefit rather than a cost of male mate choice,” said Dr Le Bas.

“Deceptive females may be more honest than they seem,” she concluded.

The research is due to be published in the October 2003 edition of Proceedings of the Royal Society of London, Series B and is currently published online at: http://www.pubs.royalsoc.ac.uk/proc _bio/proc_bio.html


Dr Le Bas is available for interview today on 01334 463 368

The authors of the paper ‘Nonlinear and correlational sexual selection on ‘honest’ female ornamentation’ are Natasha LeBas, Leon Hockham and Michael Ritchie, all of the University of St Andrews.




Issued by Beattie Media On behalf of the University of St Andrews Contact Gayle Cook on 01334 467227, mobile 07900 050 103, or email [email protected] Ref: nuptial gifts pr 280803 View the latest University news at http://www.st-andrews.ac.uk


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