toddlers, at the individual kind, understand the advantages of having a grandma close by: the excess assistance with child care, the reassuring information borne in years of expertise. In evolutionary biology, scientists call this the”grandmother effect,” and also have hypothesized it is one reason people live as long.
Currently a new study suggests that the result is not restricted to people, which killer whales also gain from getting grandmothers around. The study, published Monday in the Proceedings of the National Academy of Sciences, discovered that grandma killer bees helped enhance their grandcalves’ odds of survival, especially if food was scarce.
The findings could shed light on an enduring puzzle: why several whale species endure for many years after they go through menopause and stop repeating. The research demonstrated that, by halting reproduction, grandma killer bees prevented conflict with their replicating offspring and aided their grandcalves find enough to eat when salmon stocks blossom.
“with a living grandma enhances your survival; you are not as likely to die if she is living than in the years after her passing,” Stuart Nattrass, the study’s lead writer, and a researcher in the University of Hull, in Britain, wrote in an email.
“We have known that this is true of people and some other creatures which don’t possess menopause, like African American creatures, for a little while, also had a strong inkling that it was also accurate in those resident killer whales,” he wrote.
He and other researchers said the findings might be significant for orca conservation, implying it is just as critical to safeguard elderly, postmenopausal females since it’s younger females of breeding age and their offspring.
Worldwide, there’s estimated 50,000 killer whales, or orcas. But many populations have diminished in recent years, and a few have become jeopardized, according to the National Oceanic and Atmospheric Administration.
To assess the survival rates of killer whales in lean years, the study examined census data for two populations, off Washington State and British Columbia, as well as annual catch numbers from chinook salmon fisheries in the Pacific Northwest.
The population off Washington State has been endangered since 2005, and is now critically endangered. It has just 73 orcas and four grandmothers, according to Deborah Giles, a killer whale researcher at the University of Washington’s Center for Conservation Biology. Dr. Giles, who was not involved in the study, called that scarcity of grandmothers “startling” and “scary.”
Orca matriarchs, she said, play a critical role in the species’ survival by guiding their families to fish when stocks are low and caring for the young while the mothers of breeding age hunt.
“It’s part of what makes killer whales amazing animals,” Dr. Giles said. “They are these large-bodied, long-lived apex predators, and a lot of the life span for post-reproductive females is spent caring for, and being there with, their families. We don’t see that as readily in other species.”
Female killer whales typically start reproducing in their teens and stop in their 30s or 40s. Yet they can live well into their 80s and 90s, posing the question for scientists of why this postmenopausal stage of life has evolved. Why stop breeding if the goal is to pass on your genes?
Dr. Nattrass said the study could point to some answers. It found that postmenopausal killer whales provided the biggest boost to their grandcalves’ chances of survival, beyond that provided by grandmother killer whales that were still breeding.
“This is a particularly striking example of a case where there might be a fitness benefit to not breeding yourself — you can better help your grandkids if you’re not preoccupied with a baby of your own,” he wrote.
Dr. Nattrass said postmenopausal killer whales are able to guide their families to salmon when it’s scarce, using stores of “ecological knowledge” gained over decades of life experience. Without that knowledge, Dr. Nattrass said, the grandcalves could die.
“As salmon stocks continue to fall, the presence of these grandmothers becomes more and more important,” Dr. Nattrass wrote. “But there is going to be a point where that knowledge isn’t enough. We really need to boost salmon stocks if these grandmothers are going to be able to help their families.”
Dr. Giles recalled one striking instance of this grandmotherly help: an aerial photo, taken in 2016, that showed a killer whale known as J2, estimated to be at least 75 and possibly older than 100, catching and sharing salmon with a recently orphaned youngster, presumed to be her granddaughter. The grandmother was feeding the youngster even as she was getting thinner and thinner toward the end of her life, Dr. Giles said.
“Here’s this old, old female still trying to make sure her family members have enough food to eat,” Dr. Giles said. “She could have eaten that fish in one bite. But she didn’t.”