(TMU) — The chances of survival for young orca whales enjoys a significant boost when their grandmothers are a part of the family unit, and this is especially the case when food is scarce, according to new research.
Female orcas typically stop reproducing in their 30s and 40s, according to the study, which was published Monday in the Proceedings of the National Academy of Sciences.
While the overwhelmingly vast majority of animals die after the period in which they are able to reproduce, a tiny group of species can live decades past menopause. These creatures include orcas (or killer whales), short-finned pilot whales, belugas, narwhals, and humans.
And as it turns out, this may serve an important evolutionary function. It had long been believed that those grandmothers who live far past their reproductive age not only help care for their grandchildren but they also allow mothers to have more children, ensuring that their genes are passed down.
The study tested the idea while also finding that grandmother whales were crucial in terms of passing along knowledge about hunting for food. This was especially the case for grandmothers who were not breeding or rearing their own calves.
The study relied on 36 years of census data on two killer whale populations off the North Pacific coast of Canada and the United States, both of which were comprised of multiple pods and various family groups.
Biologist Dan Franks, a senior author of the study from the University of York, said:
“The study suggests that breeding grandmothers are not able to provide the same level of support as grandmothers who no longer breed. This means that the evolution of menopause has increased a grandmother’s capacity to help her grand-offspring.
The death of a post-menopausal grandmother can have important repercussions for her family group, and this could prove to be an important consideration when assessing the future of these populations. As salmon populations continue to decline, grandmothers are likely to become even more important in these [orca] populations.”
The study also showed how young killer whales who lost their grandmothers were far more likely to perish than those accompanied by them. The problem was especially acute in those years when salmon—a main prey for the orcas—was scarce.
The researchers believe that the grandmothers are actually filling a babysitting role for their families as the mothers hunt for fish, Franks told BBC.
“When a mother dives to catch fish, the grandmother can stay with grand-offspring.”
Darren Croft, a professor from the University of Exeter who participated in the study, said:
“Our new findings show that just as in humans, grandmothers that have gone through menopause are better able to help their grand offspring.
These benefits to the family group can help explain why menopause has evolved in killer whales just as it has in humans.”
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