It strongly appears that a menopausal mother protects her son – but not her daughter – from injuries from aggressive peers.
Female wild killer whales can live to be a respectable 90 years old. And just like humans, killer whales in menopause can live for decades. Scientists have often wondered why humans and some whale species continue to live infertile for so long. After all, what exactly is the evolutionary point if they can no longer reproduce? Previous studies have already lifted a corner of the veil. For example, it appears that menopausal killer whales play an important role in caring for their grandchildren. And now researchers have discovered another reason why these infertile females are indispensable.
Orka’s
The research team studied a group of killer whales that live off the coast of the Pacific Northwest, a region in northwestern North America. These killer whales have a so-called matriarchal society, consisting of a mother, her offspring and the offspring of her daughters. Although males reproduce with females from other groups, they too remain in the same group as their mother for life.
Bite marks
Using footage collected during photographic censuses of the killer whale population, scientists looked for evidence of “bite marks,” scars left behind when one killer whale scrapes the skin of another killer whale with its teeth. Such traces are evidence of physical social interactions and are usually created by fighting or rough play. Orcas have no natural enemies except humans. And so a bite wound is most likely caused by a conspecific.
An adult male orca with bite marks. Image: David Ellifrit, Center for Whale Research
The researchers found that a male had fewer bite marks when his mother was in menopause. “These males had 35 percent fewer bite marks than other males,” said study leader Charli Grimes. “The sons of mothers who are still reproducing did not appear to have fewer bite marks.”
Protection
According to the team, this suggests that orca mothers who have gone through menopause appear to be effective in protecting their sons from injury from aggressive conspecifics. The new study adds to growing evidence that menopausal females increase the life chances of their offspring, especially those of their sons. “We can’t say for sure why this changes in menopause,” says Grimes. “But one possibility is that menopausal killer whale mothers have more time and energy to protect their sons.”
Politierol
The researchers think older females use their experience to help their sons with social encounters. “They have a lot of experience with animals from other groups and have a lot of knowledge about behavior,” said researcher Darren Croft. “Therefore, they can lead their sons away from potentially dangerous interactions. The mothers can also intervene if a fight threatens to arise.” It means that killer whale mothers thus act as mediators and prevent conflicts from arising in the first place. “However, it is striking how targeted that social support is,” Croft continues. “It’s not like these females are playing a general police role. They only focus on their sons.”
daughters
This means that an orca mother does not interfere with her daughter’s social encounters. Why daughters don’t have to count on their mother’s protection? “Males can mate with several females,” Grimes explains. “This means that they are more likely to pass on their mother’s genes. Males also breed with females outside their social group. So the burden of raising the calf is borne by another group.”
Clap
Incidentally, an okra mother does not absorb the blows for her son. For example, the researchers discovered that menopausal females had the fewest bite marks of the entire group. This suggests that they do not physically intervene when her son ends up in a conflict that has gotten out of hand. “But she is probably present in a conflict situation, so that she can warn her son in time,” Grimes suspects.
Insights
The findings provide surprising and exciting new insights into the role of killer whale mothers in menopause. “They show protective behavior, so their sons get less wounds,” summarizes researcher Dan Franks. “It’s really fascinating to see how this mother-son relationship deepens our understanding of both the intricate social structures in orca societies, and the evolution of transition in species beyond humans.”
Moreover, according to Croft, the similarities between killer whales and humans are intriguing. “As with humans, it seems that older female killer whales play a crucial role,” he says. “Using their knowledge and experience has many benefits, including for finding food and, as it turns out, conflict resolution.”
2023-07-20 16:26:18
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