killer whale

Motherhood is a selfless act and mothers are known to make sacrifices for their offspring. However, a new study on killer whales takes this selflessness to the extreme. Killer whale mothers give up their own reproductive success to care for their sons, even after they have become full-grown adults.

„We’ve known for over a decade that adult male killer whales relied on their mothers to keep them alive, but it had never been clear whether mothers pay a cost to do so,” said Michael N. Weiss of the University of Exeter, UK, and the Center for Whale Research in the U.S.

The study, published in Current Biology on February 8, took a closer look at the „southern resident” population of killer whales in the coastal waters of Washington state and British Columbia, which has been monitored since 1976 by the Center for Whale Research.

The aim was to find out if the care adult whales, especially males, receive from their mothers comes at a measurable cost. The data showed a strong negative correlation between the number of surviving weaned sons and the annual probability of the female producing a viable calf.

„The southern resident killer whale community presents an incredible opportunity to investigate these kinds of questions,” Weiss said. „Along with their bizarre social system, where both males and females stay with their mom for life, they are also one of the best studied wild populations of mammals anywhere in the world.”

The costs couldn’t be explained by lactation or group composition effects, leading the researchers to conclude that caring for sons into adulthood is indeed a costly sacrifice. These findings offer the first direct evidence of lifetime maternal investment in any animal and reveal a previously unrecognized life history strategy.

„The magnitude of the cost that females take on to care for their weaned sons was really surprising,” Weiss said. „While there’s some uncertainty, our best estimate is that each additional surviving son cuts a female’s chances of having a new calf in a given year by more than 50%. This is a huge cost to taking care of [adult] sons!”

The benefits of keeping adult sons alive and well, however, outweigh this large cost, as the female gains evolutionary benefits when her sons are able to successfully reproduce. These findings may also have important implications for conservation efforts, as the southern residents are a critically endangered species with low reproductive rates.

This new information sheds light on a previously unrecognized factor in a female’s reproductive success and may aid in future population viability analysis.

„One big take-away is further evidence for how special (and maybe unique) the mother-son bond in killer whales is,” Weiss said. „Maybe more importantly, our study adds to the growing body of work showing the importance of animals’ social systems in determining demographic patterns. This is of central importance both for an understanding of our world and to effectively conserve endangered species.”

In future studies, the researchers aim to learn more about the nature of the costs to mother whales. They suspect that mothers may not eat enough as they continue to share food with their full-grown sons, who are already food-stressed. The primary conservation goal for the whales is to recover the population of Chinook salmon that they rely on for sustenance.

In conclusion, the ultimate sacrifice made by killer whale mothers is a testament to the strength of the bond between a mother and her son. Their selfless act offers a glimpse into the importance of social systems in determining demographic patterns and highlights the need for effective conservation efforts.

Image: Pexels.com

Source: Phys.org

Friss cikkek innen:Nature

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