News Release

After mating, fruit fly sperm no longer fully male

Peer-Reviewed Publication

Cornell University

ITHACA, N.Y. – Long considered exclusively male, a new study of fruit flies finds sperm become partly female after mating.

The paper, published in PNAS, reveals that by four days after a sperm enters a female, close to 20% of its proteins are female-derived. The researchers discovered that first seminal fluid proteins and then female proteins bind to sperm inside the female.

Some of the female proteins that attach to sperm are metabolic enzymes, which led the researchers to hypothesize they may be supporting the sperm’s viability, though more study is needed.

“In flies, and in many other organisms, sperm live for many days [inside the female], so the female may be providing enzymes they need to keep them nourished and healthy,” said Mariana Wolfner, professor of molecular biology and genetics at Cornell University, and senior author of the paper.

This study showed that although sperm come from the male and are composed of male DNA and cellular structures, once inside the female they are no longer completely male.

“If the female proteins act to stabilize sperm, you can imagine situations where reproduction could fail if a female failed to produce one of those important proteins,” Wolfner said.

Evolutionary biologists have been known to paint reproduction as male sperm working against a hostile environment within the female reproductive tract, but if sperm adopt female elements, that evolutionary argument becomes far more nuanced and likely includes aspects of molecular continuity and cooperation, Wolfner said.

Co-senior authors include Scott Pitnick, professor of biology, and Steve Dorus, associate professor of biology, both at the Center for Reproductive Evolution at Syracuse University.

For additional information, see this Cornell Chronicle story.

Cornell University has dedicated television and audio studios available for media interviews.


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