New discovery: Menopause in orcas

New research into orcas’ hunting behaviour provides a clue to the evolution of menopause.

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Orca

Just like their human counterparts, female orcas stop reproducing long before the end of their natural lives. And new research suggests why.

Menopause is very rare in the animal kingdom. The females of most species are able to reproduce throughout adulthood. However, female orcas generally stop breeding at around 40 years old, though they can survive into their 90s. In 2012, researchers found that the presence of a post-reproductive female in a pod increases the year-to-year survival of her offspring – especially her sons.

“These are not dependent offspring. These are adult killer whales whose life is part-dependent on their mother being around,” explained Exeter University’s Lauren Brent. Brent and her colleagues have now discovered how the matriarchs are helping. Their study of orcas off Vancouver Island shows that older females actively lead their pods on foraging expeditions, closely followed by their sons. This role is most pronounced when salmon, their primary food, are scarce. The post-reproductive females, it seems, are sharing a lifetime of ecological knowledge with their offspring.

Brent believes that the findings shed light on human menopause. “It’s quite logical that older individuals share information that benefits relatives,” she said. Brent cited one factor that may explain why male orcas, in particular, benefit: “Like a lot of species with sexual dimorphism), it’s make or break for males. They do either fantastically well or very badly, while females just sort of plod along and pop out a baby every five years, pretty consistently.” In which case, sons might have more to gain by learning from their mothers.

Also daughters may be less able to take advantage of their mothers’ experience. “Once they start to have their own calves, female orcas are a bit more limited in terms of their own movement,” said Brent. “The males are just a bit spoiled and get to do whatever they want.” 

Source Current Biology

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