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Why do mom killer whales live so long?

Post-reproductive mother and son.
[Photo by David Ellifrit, Centre for Whale Research]

A new study may help explain why mother killer whales live so long after having children.

Most animals must survive on their own once they reach adulthood, yet a new study published in the September 14 2012 issue of the journal Science shows that the presence of mother killer whales improves the survival of their adult sons, which in turn increases the number of grandchildren the adult sons produce.

Emma Foster from the University of Exeter and colleagues combined 36 years of demographic records and statistical modeling births to calculate the probability of survival for any individual whale at any age. (This is the same approach that life insurance companies use when working out what premium individuals should pay for life insurance.)

The researchers calculated the survival probability separately for offspring whose mothers are alive and those whose mothers died, and found that whales with long-lived mothers tended to survive longer.

The results offer evidence that female killer whales that cease reproduction but increase the survival of their adult sons can maximize the transmission of their genes without increasing competition within their own group, as would be the case when a daughter reproduces.

There is very little data available on the specific ways mothers may increase the survival of their adult sons, but assisting in foraging for food and providing support in potentially dangerous situations are possible explanations. The research team hopes to explore this question in future research.