Roach gals get less choosy as time goes by.

Females become less picky about mates as their first reproductive peak wanes, according to a new analysis of cockroach sex. The females thus become more like their male partners, who retain a lifelong willingness, to copulate with with any potential mate that moves.

Evolutionary biologist Allen J. Moore and molecular biologist Patricia J. Moore, both at the University of Manchester in England, link the females' attitude change to the costs of delay. Females forced to wait 9 days to mate after they've molted into adults bear fewer young in their first clutch than roaches that mated sooner do, the scientists report in the July 31 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES. The late starters also have fewer young over their lifetime.

Only a few studies have examined whether nonhuman females respond to a biological clock ticking away their reproductive potential. For example, William Cade, now president of the University of Lethbridge in Canada, and David A. Gray, now at California State University, Northridge, found cricket clocks. Young females bypass a male's sloppy call in favor of better crooning. Older females don't bother with such niceties.

However, Allen Moore says, he's not aware of any work before his current research that reveals the biological cost-accounting behind such behavior. Agrees Cade, "This is the study that goes a step farther."

The newly reported work focuses on novel African roaches, Nauphoeta cinerea. Unlike the familiar pests, these roaches give birth to live young and the males' fighting creates a dominance hierarchy. The scrapping males are "just like chickens," says Allen Moore.

To win a female, a male lifts his wings seductively. The researchers had previously shown that females prefer males emitting a pheromone cocktail rich in a particular ingredient. Ironically, a high concentration of that ingredient corresponds to a low position in the male's fighting hierarchy (SN: 3/3/01, p. 135).

Every romance represents a big decision for a female. She mates only once for each of the three to five clutches that she bears in her lifetime, remaining pregnant for about 40 days between matings.

To check how timing affects choosiness, the investigators tracked how long females dallied in courtship before accepting a male. They steadily shortened courtship as days passed. Females prevented from mating until after their optimal age for a first clutch courted for considerably less time than did their counterparts that mated earlier.

Allen Moore, who admits some familiarity with the steamy relationship-dramas of U.S. TV, says he would have preferred this title for the PNAS paper: "`Sex and the City' for cockroaches.