Ed Yong reports on new research from Eila Roberts, with Jacinta Beehner's research group at the University of Michigan, who was able to show that the rate of pregnancy loss among geladas (close baboon relatives) skyrockets when a new dominant male takes over a group "The Bruce effect – why some pregnant monkeys abort when new males arrive".
Geladas live in units where a single dominant male lords over several related females, whom he monopolises as mates. It’s an enviable position, and males often have to fend off takeover bids by eager bachelors. If a newcomer ousts the chief monkey, it’s bad news for the group’s females. A wave of death sweeps through the unit, as the new male kills all the youngsters whom his predecessor fathered. Indeed, babies are 32 times more likely to die after a takeover than at any other time.
But that’s not all. Eila Roberts from the University of Michigan has found that the new male’s arrival triggers a wave of spontaneous abortions. Within weeks, the vast majority of the local females terminate their pregnancies. It’s the first time that this strategy has been observed in the wild.
It really adds a new perspective to the well-known examples of male infanticide in primates. Finding early enough evidence of pregnancies and tracking their progress takes painstaking work collecting and processing fecal samples for hormone levels -- where the hormone quantities may be known only long after the researcher returns from the field with observations. The study is in the early access section of Science, which makes it hard for me to give bibliographic information, but here's the abstract.