Air Date: Week of November 7, 2003

Living on Earth’s Cynthia Graber reports on a new finding that male fowl can control their sperm when fertilizing an egg.

Transcript

CURWOOD: Just ahead: unnatural nature films. First, this Note on Emerging Science from Cynthia Graber.

[SCIENCE NOTE THEME]

GRABER: In the animal world, males often have vibrant colors or perform elaborate rituals to attract a mate to ensure their genes will be passed on. Now, scientists say males of a species of fowl have another ploy. It seems that male cockerals can regulate the amount of sperm they ejaculate. Females cockerels have multiple sex partners. So scientists in England developed a novel method. They harnessed female cockerals with a special contraption to collect ejaculated semen.

The researchers then controlled which female was presented to each male. They also controlled whether or not other males were present during copulation. They analyzed the resulting sperm and found that males who mated with the same female numerous times reduced the amount of sperm with each successive copulation and eventually stopped mating with the female altogether. But when a new partner came along, the level of sperm went up again. The level of sperm was also higher when another male was present during copulation. Scientists say each male has a limited number of sperm. Rationing how much of it goes into each partner may raise the chances of a successful fertilization. That’s this week’s Note on Emerging Science, I’m Cynthia Graber.

CURWOOD: And you're listening to Living on Earth.

[MUSIC: Thomas Newman “Mr. Smarty-Man” AMERICAN BEAUTY – ORIGINAL MOTION PICTURE SCORE(Dreamworks – 2000)]