Male killer whales protected by post-menopausal mothers, study suggests

;Male killer whales In an article published in the journal Current Biology, scientists found that postmenopausal orcas protect their calves

By Ground report 22 Jul 2023

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Male killer whales protected by post-menopausal mothers, study suggests

In an article published in the journal Current Biology, scientists found that postmenopausal orcas protect their calves so they don't get badly hurt in fights with other orcas.

The study indicates that when the mother, who has already stopped reproducing, is present, males have fewer tooth marks, which turn into scars. The female pups did not observe this phenomenon.

The researchers analyzed approximately 7,000 photographs of orcas found off the Pacific coast of North America. They have been tracking these orcas for 50 years. Fights with other orcas cause the scars from tooth marks since humans are their only natural predators.

The Fascinating World of Orcas

Scientists in the journal Current Biology discovered that postmenopausal orcas actively protect their calves from severe injuries during fights with other orcas. The study revealed that male offspring displayed fewer tooth marks, which eventually turn into scars, when their non-reproductive mothers were present. However, the researchers did not find any evidence of such behavior in female pups.

The results showed a fascinating pattern: Male killer whale calves showed fewer teeth marks and scarring when their post-productive mothers were present. These wise matriarchs seemed to intervene during aggressive interactions, providing support and protection to their male offspring. This maternal behavior helped reduce the risk of infections and mortality resulting from socially inflicted injuries.

As Charli Grimes, a researcher at the University of Exeter and lead author of the study, explained to The Guardian, "The motivation for this project was really trying to understand how these post-reproductive females are helping their young."

Female killer whales live for around 90 years and more than 20 after menopause. According to previous studies, postmenopausal orcas help extend the lifespans of their children and grandchildren by bringing the fish they catch back to their pods. For the researcher, the results of the study "highlight a new way by which menopause is adaptive in orcas."

Charli Grimes, lead author of the study, explained, "The motivation for this project was really trying to understand how these post-reproductive females are helping their young." The research has highlighted an entirely new dimension of menopause's adaptive role in orcas, demonstrating that these grandmothers play a crucial role in enhancing the survival and reproductive success of their male offspring.

Postmenopausal orcas protect male offspring

While menopause is a well-known phenomenon in humans, the reason behind its existence in certain animal species remains a subject of curiosity and scientific investigation. Female killer whales, like humans, can live many years beyond their reproductive phase, and previous research has shown that postmenopausal killer whales continue to contribute to the survival and well-being of their social groups by sharing resources and ecological knowledge.

It makes sense to the researchers that fewer markings were evident in the male pups. “Males can breed with multiple females, so they have more potential to pass on their mother's genes. Also, males breed with females outside of their social group, so the burden of raising the young falls on another pride,” he noted.

For now, it is not clear how the mothers influence the confrontations to be less aggressive for the males. According to Grimes, “It could be that they use their enhanced knowledge of other social groups to help their children navigate risky interactions. They could be telling their kids to avoid conflict." Although it is also a possibility that they get involved in conflicts.

The mystery of supporting female offspring

An intriguing aspect of this study was that the protective influence was specific to the male offspring. The researchers speculated that this preference might be due to the unique social structure of resident killer whale populations.

Male killer whales typically remain in close association with their mothers throughout their lives, resulting in a stronger bond between mothers and their adult offspring. This strong bond allows post-reproductive females to offer support to their male offspring during aggressive interactions with other males, potentially enhancing their reproductive success.

Unlike male calves, female killer whale calves did not exhibit the same level of protection against rake marks when their postmenopausal mothers were present. The reason for this differential treatment is not yet fully understood. Female calves may receive support and benefits in other ways, such as sharing ecological knowledge and transferring resources. More research is required to unravel the complexities of this intriguing behavior.

Menopause remains an evolutionary puzzle in many species, challenging traditional life history theories that predict no selection for survival after cessation of reproduction. In the case of human societies and certain toothed whales, including orcas, females continue to live well past their reproductive years, contradicting earlier hypotheses.

Kinship dynamics and menopause in orcas

The study also explored the role of kinship dynamics in the evolution of menopause in resident killer whales. As female orcas age, their relationship with their social group increases, leading to increased helping behavior and reduced reproduction, according to kinship dynamics theory. This scenario aligns with observations in killer whales, where older females gradually stop reproducing and instead focus on supporting their relatives.

Post-reproductive female killer whales not only protect their male calves, but also act as repositories of ecological knowledge, guiding their social units to find food sources. These grandmothers' deep knowledge of other social groups could also help them navigate risky interactions and avoid conflict during intergroup encounters.