Canada Press: It's a female lizard's life

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Posted by desiree on November 05, 2002 at 10:35:44:

It's a female lizard's life
Last Updated Tue, 05 Nov 2002 9:46:38
LOS ANGELES, CALIF. - The female side-blotched lizard not only selects her mates, she even decides if she'll have sons or daughters, biologists reported Tuesday.

The lady lizard exercises full control of the species mating and reproductive cycles. It's as if she selects the best place to live, the wealthy but homely mate and a handsome lover.

Choosy female lizard
Courtesy: Ryan Calsbeek
The rock-dwelling lizard is found west of the Rocky Mountains from Canada to Mexico's Baja Peninsula. The male side-blotched lizard is about 5.8 centimetres in size, and the female half that.

Biologist Ryan Calsbeek of the UCLA Center for Tropical Research studied about 100 side-blotched lizards living among the rocks in southern California.

In the natural world, the fittest males tend to choose the best territory. Among side-blotched lizards, the female picks the mate she lives with. She sets her sights on the biggest male who lives on the biggest rock in the best location.

In his experiment, Calsbeek wanted to determine whether the female was selecting the best living site or the best mate. To find out, he did some heavy lifting.

Calsbeek hauled about 680 kilograms of rocks around for three years and observed the lizards' reactions.

The researchers tried putting big males onto poor rocks and smaller males on the best rocks and then watched what happened.

Female seeks big males, big rocks

Once males establish their rock boundaries, they generally don't move, Calsbeek said. But the female can move around, and she does.

The researchers observed the females leaving their first male and live-in partner in favour of smaller males in new territory. She seems to have a taste for fancy rocks.

But the female is also "incredibly promiscuous" and mates with five or six males per reproductive cycle.

After some paternity tests, the researchers determined the female is able to collect sperm from her many partners in a special body cavity before her eggs are fertilized.

Sex selection

Somehow, the female is able to cause sperm from the big males to make sons, while the sperm from small males were used to make daughters.

"The genetic data was so amazing," Calsbeek told CBC News Online. "I was just staring at the computer screen going 'no way.' The degree of control is astounding."

The researchers don't understand how the females do it. Calsbeek speculates cellular surface proteins on the sperm signal the presence of X or Y chromosomes that the female's physiology can interpret.

MORE SCIENCE NEWS from:cbc.ca/science

The study appears in Tuesday's issue of the Proceedings of the National Academy of Sciences.

It's a female lizard's life

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