New male spells death for unborn monkeys

WHEN a new leader takes control of a troop of gelada monkeys, he is likely to kill the offspring of his predecessor. His arrival is also bad news for young yet to be born: they'll be aborted within weeks.

Named for Hilda Bruce who first observed it in mice, the "Bruce effect" is common in lab animals. In fact, some biologists suspect it is an artefact of keeping animals in labs. Jacinta Beehner of the University of Michigan in Ann Arbor and colleagues have now found evidence of the effect in wild geladas (Theropithecus gelada), an Ethiopian monkey related to baboons.

They found that the number of births fell sharply in the six months after a new dominant male took over a group, suggesting females were aborting their fetuses. As a check, Beehner took hormone samples from females' faeces, allowing her to track 60 pregnancies closely. Of nine failures, eight occurred in the two weeks after the father was replaced.

Beehner says the strategy makes sense, because females don't want to waste energy on offspring likely to be killed after they are born.

We don't know how the females do it, says Peter Brennan of the University of Bristol, UK, who was not part of the study. It may simply be a response to the stress of the takeover.

Journal reference: Science, DOI: 10.1126/science.1213600

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