Why Grandma Orcas Go Through Menopause

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Female killer whales, like their human counterparts, live decades beyond their reproductive years.

Scientists are trying to figure out why. In doing so, the researchers aim to uncover more clues about the evolutionary purpose of menopause – a rare phenomenon in the animal kingdom.

Previous research suggested that postmenopausal killer whales are believed to increase the life chances of their offspring and grandchildren – known as the grandmother effect. The leader of a pod of killer whales shares her knowledge of the best hunting spots and more than half of the fish she catches with her family members.

Now, according to a new study published Thursday in the journal Current Biology, these orca matriarchs, who can live to be 90, also enjoy spending their final years indulging in helicopter parenting of their sons. Female orcas help their sons navigate the complexities of orca social life and protect them from fights with other killer whales.

In a group of orcas, known as Southern resident populationwhich lives off the Pacific Northwest coast of North America, scientists have studied “tooth rake marks” – the scars left when one whale scratches its teeth on another’s skin.

The research team found that males had 35% fewer marks if their mother was present and had stopped breeding, according to analysis of data and images collected by the study. Whale Research Center in Friday Harbor, Washington. The center studied this critically endangered group killer whales, which now number about 75, since 1976. Some 103 orcas were involved in the research due to births and deaths during the study period.

Killer whales have no natural predators – except for humans – and the teeth marks on their skin can only be inflicted by other killer whales, either within social groups or when two pods meet.

“Tooth rake marks are indicators of physical social interactions in killer whales and are typically obtained through violent fighting or play,” said study lead author Charli Grimes, an animal behavior scientist at the Center. in Animal Behavior Research from the University of Exeter in the UK.

It was possible that older females used their experience to help their sons during encounters with other whales, Grimes said. The team is collecting drone footage of the whales to better understand the behavior.

“We believe these women are using their in-depth knowledge of other social groups that obviously comes with time (and) experience…to help their sons navigate the interaction – whether vocally or behaviorally,” she said. “It’s a guess on how they might protect them. Another is that they get involved in a conflict if a fight seems risky (for their son).

Researchers have found no evidence that postmenopausal killer whales – who can expect to live around 22 years on average after they stop breeding – reduce bite marks on their daughters. Nor did reproductive mothers or grandmothers reduce the rate of these socially inflicted injuries on their offspring.

“We can’t say for sure why this changes after menopause, but one possibility is that stopping reproduction frees up time and energy for mothers to protect their sons,” Grimes said.

Why not protect the orc girls? Grimes said it makes more evolutionary sense for Orc matriarchs to focus on their sons, because they have more potential to pass on their mother’s genes – and in a way that doesn’t place any additional burden on the child. band.

“Males have the ability to mate with multiple females, and they do so outside of their own social group. When a male’s calf is born…then the cost of that calf falls on the other group,” said she declared.

Only humans and five species of toothed whales are known to experience menopause, according to the new study. However, a August 2021 study suggested that the grandmother effect may also occur in female giraffes, which live well beyond their reproductive years.