July 20 () –
Postmenopausal female killer whales protect their youngbut not their daughters, from fights with other whales, new research shows, published in the journal Current Biology.
The scientists studied the “dental razor marks” — the scars left when one whale scrapes the skin of another with its teeth — and found that the males had fewer marks if their mother was present and had stopped breeding.
Only six species — humans and five species of toothed whales — experience menopause, and scientists have long wondered why it happens. The new study, carried out by the Universities of Exeter and York, in the United Kingdom, and the Center for Whale Research (United States), adds to the growing evidence that postmenopausal females increase the life chances of their young, especially males.
“We were fascinated to discover this specific benefit for males with their post-breeding dam. says lead author Charli Grimes, from the University of Exeter’s Center for Animal Behavior Research. These males had 35% fewer teeth marks than other males. For males whose mother continued to breed, we found no evidence that her presence reduced dental rake injuries.”
“We can’t say for sure why this changes after menopause, but one possibility is that the cessation of reproduction frees up time and energy for mothers to protect their children,” she continued. Tooth rake marks are indicators of physical social interactions in killer whales and are typically obtained through fighting or horseplay.“.
The study is part of a long-term investigation of “southern resident” orcas, which live off the Pacific coast of North America. The body of evidence suggests that — rather than competing with their daughters to reproduce — female orcas have evolved to pass on their genes to help their children and grandchildren.
As to why females focus their efforts on their offspring, Grimes notes that “males can breed with multiple females, so they have a better chance of passing on their mother’s genes. Also, males breed with females outside their social group, so the burden of raising the young falls on another pod.”
The southern resident orcas feed on salmon and have no natural predators other than humans, so tooth marks on their skin can only be inflicted by other orcas. This can occur within social groups or when two packs meet.
According to Professor Darren Croft, also from the University of Exeter, it is not known exactly how mothers protect their young, but “it is possible that older females use their experience to help their young in social encounters with other whales. They will have previous experience with individuals from other packs and knowledge of their behavior, so they could steer their young away from potentially dangerous interactions.. And mothers could also step in when a fight seems likely.”
“The similarities to humans are intriguing,” he continued. “Like humans, it appears that older female whales play a vital role in their societies, using their knowledge and experience for benefits, such as foraging and resolving conflict.”
For his part, Professor Dan Franks, from the Department of Biology at the University of York, highlights that these findings offer “a captivating insight into the role of postmenopausal orca mothers. They carry out protective behavior, reducing the incidence of socially inflicted injuries to their children.
“It is fascinating to see how this postmenopausal mother-infant relationship deepens our understanding of both the intricate social structures of orca societies and the evolution of menopause in species other than humans.”