MAMA'S BOYS
Male killer whales protected by post-menopause mothers
IMAGE: AN ADULT MALE WITH DEEP TOOTH RAKE MARKS view more
CREDIT: DAVID ELLIFRIT / CENTER FOR WHALE RESEARC
Post-menopause female killer whales protect their sons – but not their daughters – from fights with other whales, new research shows.
Scientists studied “tooth rake marks” – the scarring left when one whale scrapes their teeth across the skin of another – and found males had fewer marks if their mother was present and had stopped breeding.
Only six species – humans and five species of toothed whales – are known to experience menopause, and scientists have long been puzzled about why this occurs.
The new study – by the universities of Exeter and York, and the Center for Whale Research – adds to growing evidence that post-menopause females boost the life chances of their offspring, especially males.
“We were fascinated to find this specific benefit for males with their post-reproductive mother,” said lead author Charli Grimes, from the Centre for Research in Animal Behaviour at the University of Exeter.
“These males had 35% fewer tooth marks than other males.
“For males whose mother was still breeding, we found no evidence that her presence reduced tooth rake injuries.
“We can’t say for sure why this changes after menopause, but one possibility is that ceasing breeding frees up time and energy for mothers to protect their sons.
“Tooth rake marks are indicators of physical social interactions in killer whales and are typically obtained through fighting or rough play.”
The study is part of long-term research on “southern resident” killer whales, which live off the Pacific coast of North America.
The body of evidence suggests that – instead of competing with their daughters to breed – female killer whales have evolved to pass on their genes by helping their children and grandchildren.
Commenting on why females focus efforts on their sons, Grimes said: “Males can breed with multiple females, so they have more potential to pass on their mother’s genes.
“Also, males breed with females outside their social group – so the burden of raising the calf falls on another pod.”
Southern resident killer whales feed on salmon and have no natural predators apart from humans, so tooth marks on their skin can only be inflicted by other killer whales.
This may happen within social groups, or when two pods meet.
Commenting on how mothers protect their sons, Professor Darren Croft, also from the University of Exeter, said: “We can’t say for sure.
“It’s possible that the older females use their experience to help their sons navigate social encounters with other whales.
“They will have previous experience of individuals in other pods and knowledge of their behaviour, and could therefore lead their sons away from potentially dangerous interactions.
“The mothers might also intervene when a fight looks likely.”
Professor Croft added: “The similarities with humans are intriguing.
“Just as in humans, it seems that older female whales play a vital role in their societies – using their knowledge and experience to provide benefits including finding food and resolving conflict.”
Professor Dan Franks, from the Department of Biology at the University of York, said: "Our findings offer captivating insights into the role of post-menopausal killer whale mothers.
“They perform protective behaviour, reducing the incidence of socially inflicted injuries on their sons.
“It's fascinating to see this post-menopausal mother-son relationship deepening our understanding of both the intricate social structures in killer whale societies and the evolution of menopause in species beyond humans."
The study was supported by the Natural Environment Research Council.
The paper, published in the journal Current Biology, is entitled: “Postreproductive female killer whales reduce socially inflicted injuries in their male offspring.”
An adult male with travelling with its post-reproductive mother
CREDIT
David Ellifrit / Center for Whale Research
A whale breaching
CREDIT
Astrid Van Ginneken / Center for Whale Research
JOURNAL
Current Biology
METHOD OF RESEARCH
Observational study
SUBJECT OF RESEARCH
Animals
ARTICLE TITLE
Postreproductive female killer whales reduce socially inflicted injuries in their male offspring
ARTICLE PUBLICATION DATE
20-Jul-2023
Post-menopause orca mothers protect their sons from being injured by other orcas
IMAGE: AN ADULT MALE ORCA WITH TOOTH RAKE MARKS view more
CREDIT: COPYRIGHT DAVID ELLIFRIT, CENTER FOR WHALE RESEARCH
Female killer whales live up to ninety years in the wild, and most live an average of twenty-two years after menopause. Scientists have long wondered why humans and some whale species spend a significant portion of their life not reproducing. Previous studies show that, even after having their last calf, killer whale mothers take care of their families by sharing the fish they catch. Now, in a study published on July 20 in the journal Current Biology, researchers note that these mothers can also provide social support to their sons by protecting them from being injured by other orcas.
“The motivation of this project was really to try and understand how these post-reproductive females are helping their offspring,” says first author Charli Grimes, an animal-behavior scientist at the University of Exeter. “Our results highlight a new pathway by which menopause is adaptive in killer whales.”
The research team studied southern resident orcas, a group of orcas that live off the Pacific Northwest coast. These killer whales live in matriarchal social units that consist of a mother, her offspring, and the offspring of her daughters. Although male orcas will outbreed with whales from other pods, both males and females stay in their unit of birth, with their mother, for life.
Using data from the Center for Whale Research’s annual photographic census of the orca population, the researchers looked for evidence of scarring on each catalogued whale’s skin. Killer whales have no natural predators other than humans, so a tooth mark that is able to puncture an orca’s skin was most likely inflicted by another orca.
The study found that, if a given male’s mother was still alive and no longer reproducing, that male would have fewer tooth marks than his motherless peers or his peers with a mother who was still reproducing.
“It was striking to see how directed the social support was,” says senior author Darren Croft (@DarrenPCroft), an animal-behavior scientist at the University of Exeter. “If you have a post-reproductive mother who’s not your mother within the social group, there’s no benefit. It’s not that these females are performing a general policing role. These post-reproductive mothers are targeting the support they are giving to their sons.”
The researchers still can’t say for certain what kinds of social conflicts are leading to tooth marks or how older females are protecting their sons against them. They do note that post-menopause females have the lowest incidence of tooth marks in the entire social unit, suggesting that they do not physically intervene in a conflict. If older orca females play a similar role to that of older women in human societies, they might be acting as mediators, preventing conflict from occurring in the first place. To explore this further, the researchers plan on completing an additional study by using drone footage to observe whale behavior from above.
“It’s possible that with age comes advanced social knowledge. Over time, they might have a better understanding of other social groups,” says Grimes. “Given these close mother-son associations, it could also be that she is present in a situation of conflict so she can signal to her sons to avoid the risky behavior they might be participating in.”
“We’ve got hypotheses, but we need to test them by seeing what’s happening under water when these different groups interact,” says Croft. “We’ve learned so much from this population, but we’ve still got so much to learn from them.”
###
Current Biology, Grimes et al. “Postreproductive female killer whales reduce socially inflicted injuries in their male offspring” https://www.cell.com/current-biology/fulltext/S0960-9822(23)00824-2
This work was supported by the Natural Environment Research Council. The authors declare no conflicts of interest.
Current Biology (@CurrentBiology), published by Cell Press, is a bimonthly journal that features papers across all areas of biology. Current Biology strives to foster communication across fields of biology, both by publishing important findings of general interest and through highly accessible front matter for non-specialists. Visit: http://www.cell.com/current-biology. To receive Cell Press media alerts, contact press@cell.com.
A post menopause female orca traveling with her adult son
CREDIT
Copyright Center for Whale Research
JOURNAL
Current Biology
METHOD OF RESEARCH
Observational study
SUBJECT OF RESEARCH
Animals
ARTICLE TITLE
Postreproductive female killer whales reduce socially inflicted injuries in their male offspring
ARTICLE PUBLICATION DATE
20-Jul-2023
No comments:
Post a Comment