In the lab, female rodents sometimes terminate their pregnancies after being exposed to new males. It’s called the Bruce effect, for researcher Hilda Bruce. Now a study in the journal Science finds that the Bruce effect occurs in the wild, and likely ups evolutionary fitness. [Elia K. Roberts et al, A Bruce Effect in Wild Geladas]

To discover whether the Bruce effect is a naturally occurring adaptive strategy, researchers from the University of Michigan observed a wild population of gelada monkeys. They measured hormones in the animals’ feces to identify pregnant females and their conception dates.

Gelada monkeys live in small groups, with several females and a single male. When a rival displaces the male in a gelada family, he frequently kills his predecessor’s progeny. And the females know it. The researchers found that females impregnated by the old male terminate 80 percent of their pregnancies after the new male takes over.

Those females were quicker to conceive again with the new male than were females who hadn’t been pregnant. Rather than producing offspring at risk of death, females subject to the Bruce effect invest in new progeny—with a better chance of survival.

—Sophie Bushwick

[The above text is a transcript of this podcast.]