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... 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...Further details are published in the Science article, nicely summarized at Not Exactly Rocket Science. The mechanism of the abortion is not readily apparent; one supposes that it occurs because of alterations in hormonal balances.
It’s obvious why the incoming males kill any existing infants. Female geladas don’t become fertile until they stop raising their existing children. Assuming no abortions, they go for three years between pregnancies. That’s longer than the typical reign of a dominant male. So, a newcomer, having finally won the right to mate, has few opportunities to actually do so. To make things worse, his females are busy raising someone else’s children. His solution: kill the babies. The quicker he does this, the sooner the females become fertile again, and the sooner he can father his own children.
But why would a pregnant female abort her own foetus? Roberts thinks that it’s an adaptive tactic in the face of a new male’s murderous tendencies. Since the male would probably kill the newborn baby anyway, it’s less costly for the female to abort than to waste time and energy on bringing a doomed infant to term. Her future offspring, conceived more quickly and fathered by the incumbent king of the hill, will stand a better chance of survival.
27 February 2012
"Adaptive" spontaneous abortions
Named after its discoverer, the "Bruce effect" is a phenomenon in which pregnant female geladas (relatives of baboons) abort their fetuses when a new male becomes dominant:
Subscribe to: Post Comments (Atom)
....and people still believe in a god.ReplyDelete
Why would spontaneous abortion be incompatible with belief in a god?Delete
You'd think an all-knowing, all-powerful being would have a better solution to things than "Kill off the babies."Delete
Still, it provides a nice foil to the bible-thumpers who state what is and is not 'natural.'
Huh. Something doesn't add up in my head.ReplyDelete
1. females go 3 years between pregnancies (presumably because they are raising their offspring)
2. the reign of a dominant male is <3yrs
3. dominant males kill offspring that isn't theirs
How do any offspring survive then?
I think the dominant only kills infant offspring, so any that matured during a reign would survive a regime change (to one day potentially challenge for supremecy themselves).Delete
A nursing infant would preclude a new mating (no estrus in the female), and a chance for the new male to father another baby with his genetics. An older offspring does not affect the ability to pass along genetics.Delete
It is common in rodents.ReplyDelete
Also...people seem to be getting confused. The Bruce effect is NOT the killing of already-born infants. The Bruce effect is the ending of pregnancies, with no physical harm from any male.ReplyDelete
http://en.wikipedia.org/wiki/Bruce_effect Plenty of layperson strength information there on the hormonal "mechanism".ReplyDelete
Different Anny than the ones above...ReplyDelete
Interesting. I had not heard of animals doing this chemicaly, though now I have. I had read that horses, for example, as well as wild cats, etc, also undergo "spontaneous" abortion when the male leader changes, but this is because the new male harrasses and forces himself on each eligible female, leading to a miscariage of any pregnancies. (for reference, see Stephen Budiansky's book "The Nature of Horses", c1997, page 97-98) You can learn new things everyday.
what references does Stephen Budiansky use to back up that claim?Delete