Overly Dependent Male Killer Whales Take a Long-Term Burden on Mothers »Explorersweb

In news that mothers everywhere will understand, a new study found “no evidence that sons became less expensive as they aged” and “men were still expensive regardless of age.”

If you’ve just felt a wave of filial guilt, don’t worry. The research is about the maternal behavior of killer whales and not about you (unless your mother sent you this link).

In a study published in the journal Current Biology, scientists looked at decades of census data from a well-studied killer whale population. They discovered something interesting: female killer whales pay a reproductive price for the prolonged care they show their male calves.

In short, orca mothers with male calves are less likely to reproduce than their peers with female calves. And killer whales that have given birth to multiple daughters tend to stop breeding after having a male calf.

“This negative effect did not abate as sons grew, and son cost could not be explained by long-term lactation costs or group composition effects, supporting the hypothesis that which caring for adult sons is reproductively costly,” the authors of the paper wrote. .

a chart explaining how orca mothers have fewer young while caring for their adult sons

A female killer whale is likely to stop breeding after having a male calf. Graphic: Michael N. Weiss et al.

Why are orc girls easier?

The authors hypothesize that the cost of reproduction may come from prey-sharing behavior. Splitting kills with adult sons reduces the nutritional intake of an adult female, directly affecting her fertility.

But what about the girls? Scientists have asked themselves the same question. After analyzing the numbers, they “found no evidence that daughters influenced the reproductive success of their mothers.” This result is not entirely surprising, as killer whales are known to care for their sons until adulthood, but stop caring for their daughters soon after they reach maturity. sexual.

“For more than a decade, we’ve known that adult male killer whales depend on their mothers to keep them alive, but it’s never been clear whether mothers pay a price for doing so,” said the lead author. Michael Weiss from the University of Exeter. El Pais.

an orca hunts seals in the shallows

A killer whale hunts off Patagonia. If that orca is female and has a son, she will share her catch with him until adulthood, sacrificing her own fertility to do so. Photo: Shutterstock

“The magnitude of the cost that females bear to care for their weaned offspring is truly staggering. Although there is some uncertainty, our best estimate is that each additional surviving offspring reduces a female’s chances of having a new brood in any given year by more than 50% is a huge price to pay for caring for already adult offspring!

The maternal behavior of killer whales is quite unusual in the natural world. Only certain species of monkey (including the monkey reading this) show such devotion and long-term care. In fact, outside of humans, killer whales have the longest post-reproductive lifespan of any animal.

But good mother monkeys are no less likely to reproduce after having sons. Only killer whales do – putting fascinating cetaceans in a category of their own.

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