Benefits of grandmothering may have played a major role in the success of older female orcas (killer whales) but the costs of being outcompeted by their daughters apparently play a role in the emergence of their menopause, a new study suggested.
The scientists teamed up with the Center for Whale Research, and Fisheries and Oceans Canada to test this hypothesis on killer whales through a long-term dataset. The study was published in the journal Current Biology. They found that this trend puts off mother orcas from reproduction, which in turn make them more focused on raising their younger members of their families instead. Image credit: AP/Elaine Thompson.
Anthropologist Kristen Hawkes, at the University of Utah, says the killer whales are fascinating, but that they're hard to study. This exhaustive investigation allowed the scientists to determine that aged whales found difficulty when competing with their daughters when it comes to reproduction. But this wasn't the case when mothers and daughters bred at the same time, when calves born to older females were 1.7 times more likely to die.
Professor Darren Croft explains that "older females are more closely related to the family group than younger females".
A couple of orcas.
Earlier studies conducted by a team of scientists from the University of Exeter, University of York, and the Center for Whale Research showed that females in another group or species act as leaders and continue to reproduce even as they grow older in life.
Killer whales, short-finned pilot whales, and humans are the only species known to go through menopause.
Professor Cant said: "It's great that our theoretical predictions, made seven years ago, turned out to be correct". He stated that not only the scientists have discovered the key that explains menopause, but also why post-reproductive and older specimens often live longer.
He said the study concluded older female whales go through menopause because they lose out in the reproductive competition with their daughters. Along with humans, the killer whale is just one of a few species on Earth known to get menopause, and a new study of the ocean-dwelling creature may have just answered the baffling mystery of why women get it at all, or at least gotten us closer to the answer.
However, according to Dr. But the exact reasons for it in killer whales (known formally as Orcinus orca) have remained up for debate. But our new work shows that if an old female killer whale reproduces her late-life offspring suffer from being out-competed by her grandchildren.
Certainly, long beyond their most fertile years, older females play crucial roles in the lives of many social mammals. They become dependent on their mothers for their survival. All the populations included several family groups that helped to the understanding of the behavior of every pod member. Currently, this whale group includes 24 members that were led by J2 (the "grandmother"), which died this month. One of these pods - known as J pod, which now consists of more than 20 individuals - was led by J2, or Granny, the killer whale matriarch.
Killer whales and humans would seem to have little in common. Giles explained that her ability to gather the members of the pod was unbelievable. They feast on seals, sea lions, fish and even other whales.
The bottom line, Croft says, is that menopause is no accident.
The paper concludes that "The lower survival of calves from older generation mothers in reproductive conflict can not be explained due to a general effect of mother's age on offspring survival as we found no effect of mother's age on offspring survival to age 15 across all calves born during the study period". These findings are fundamental to understanding why killer whales have so efficient survival rates and also becomes essential as several populations that were under investigation are considered endangered species.