Benefits of Menopause: Good Fishing

Humans can't understand whale communication, but if they did, they might hear this familiar refrain: “Give Grandma some respect; she has been around!" Post-menopausal killer whales (Fig. 1) are community leaders, with expertise in finding food when the salmon runs are poor, suggests an analysis of 751 hours of videos of resident whales in Washington and British Columbia [1]. The findings hint that the transfer of ecological knowledge to kin by older females may have partly driven the evolution of menopause. Resident orca whales in the Salish sea. Everyone stays with the family! Image courtesy NOAA. In only a handful of species do the females survive for decades after their reproductive years—humans, pilot whales, and killer (orca) whales. In humans, several studies have showcased the fitness benefits of being a grandmother—for instance, pre-modern Finnish and Canadian women who lived long lives had more grandchildren than women who died soon after menopause. As with human hunter-gatherer groups (our evolutionary crucible), the resident orca whales of Puget Sound and British Columbia have a tight-knit society. And perhaps whale bonds are even tighter—human hunter-gatherer girls and women were thought to eventually leave the group, say the researchers, whereas female and male whale offspring do not leave their mother's pod. Previous studies have shown that adult whales are much more likely to die in the year after their mother's death. In the new study, Lauren Brent et al. identified one key way older females contribute to the fitness of their offspring. They found that older females were much more likely than other whales to lead pods as they roamed through coastal waters, trolling for salmon—their primary source of food. What's more, during years when salmon runs were scarce, the fraction of older females leading pods increased substantially. The findings suggest that older females serve as a repository of ecological information, enabling whales to survive when food is scarce. As a female ages, her relatedness to her group increases as her offspring reproduce, and her accumulated knowledge in turn benefits these kin. Whales have complex, fluid societies, which humans barely understand. For instance, some orca whales—not part of this study—live in migratory groups that hunt seals. As another example, male whales, who rarely live past 50, seem more dependent on their mothers than do females, and are more likely to die after she dies. Perhaps mom puts more resources into males since they mate outside the pod, increasing her reproductive success with less strain on the pod's food resources, speculate the researchers. It is likely that menopause is about more than finding food, say the researchers. Throughout the long lives of these sophisticated creatures, older female whales may help younger animals navigate a complex range of social and environmental situations.

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