Menopause is the strangest thing seen only in three species, humans, killer whales and pilot whales throughout the animal kingdom. Killer whales live up to 90 years and females start breeding from 12 to 40 years of age. Female killer whales live for over 40 years after menopause where they cannot bear any children. So how these old female whales are helpful to the pod or community has been a mystery.
A new study from Universities of Exeter and York (UK) and the Center for Whale Research (USA) has shown that female killer whales live long after menopause and help their family members find food during hard times. This research provides insights into why women continue to live long after they can no longer have children. Research team collected information over the last 35 years from the observations made on a total of 102 individual southern resident killer whales (Orcinus orca) in the North Pacific Ocean, off the coasts of the USA and Canada. The team has monitored various aspects including birth and death dates as well as more complex data, like the genetic and social relationships between the different animals.
Researchers found that post-reproductive female killer whales act as ‘repositories of ecological knowledge’, leading groups when they are moving together in salmon foraging grounds. Critically, the researchers discovered that leadership by menopausal females is especially prominent in difficult years when there are fewer salmon. Shortage of salmon is a major contributing factor to mortality in this population and so the benefits of older females knowing when and where to find salmon could be considerable.
Lauren Brent of the University of Exeter’s Centre for Research in Animal Behaviour said: “Our results show for the first time that one way post reproductive females may boost the survival of their kin is through the transfer of ecological knowledge. The value gained from the wisdom of elders can help explain why female killer whales and humans continue to live long after they have stopped reproducing.”
“In humans, it has been suggested that menopause is simply an artefact of modern medicine and improved living conditions,” said Professor Darren Croft of the University of Exeter. “However, mounting evidence suggests that menopause in humans is adaptive. In hunter-gatherers, one way that menopausal women help their relatives, and thus increase the transmission of their own genes, is by sharing food. Menopausal women may have also shared another key commodity – information.”
The researchers also found that females are more likely to lead their sons compared to their daughters. Dr Daniel Franks of the University of York explained: “Killer whale mothers direct more help toward sons than daughters because sons offer greater potential benefits for her to pass on her genes. Sons have higher reproductive potential and they mate outside the group, thus their offspring are born into another group and do not compete for resources within the mother’s matriline. Consistent with this, we find that males follow their mothers more closely than daughters.”
The study was published in the journal Current Biology, titled ‘Ecological knowledge, leadership and the evolution of menopause in killer whales’ by Lauren Brent, Daniel Franks, Emma Foster, Kenneth Balcomb, Michael Cant and Darren Croft. The study was supported by Natural Environment Research Council