Some Females Too Sexy for Own Good, Fly Study Says

Brian Handwerk
for National Geographic News
December 29, 2009

There is a price to beauty: "Sexier" female fruit flies suffer more than unattractive ones, according to a new study.

The most fetching female fruit flies—that is, the biggest females, which can produce the most eggs—were inundated with suitors and hatched fewer babies than less desirable flies, said study leader Tristan Long, an evolutionary biologist at the University of Toronto.

The reason is twofold: The repeated advances hindered the females' ability to find food, and too much sex left the females overloaded with toxic semen, Long said.

(Related: "Female Flies Put Up a Fight to Keep Sex Short.")

Fruit flies are commonly used in lab studies, because the animals' roughly monthlong life spans allow scientists to quickly identify trends across generations.

Selfish Sex

Long and colleagues first developed a series of graphic models that predicted that too much male fruit fly persistence would harm the females' reproduction.

When the team put an individual male in an area that contained a large and a small female, the male would pester the larger female more than the smaller female.

Then the researchers compared lifetime fertility rates between large and small females either minimally or continuously exposed to males. In the continuously exposed group, the results showed that larger females had lower fertility rates than smaller females.

The findings, published December 8 in the journal PLoS Biology, fuel an ongoing debate about whether sexual selection and natural selection are always complimentary, Long said.

Natural selection promotes the genes that increase the likelihood of survival, while sexual selection promotes those genes that boost the odds of reproductive success.

"To a certain extent it's recognized that maybe the most attractive individuals may be attractive because they carry the best genes," Long said.

Continued on Next Page >>




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