Killer whales may have menopause so grandma can look after the kids

17 October 2013

Killer whales are just one of three species - we're one of the others - that continue to live long after they've stopped reproducing. But scientists still don't know why these three alone evolved this unusual menopausal trait.

In a bid to find out, NERC has agreed to fund a project worth nearly £500,000 to look at why killer whales stop reproducing a third of the way through their lives, dedicating the rest of their lives to protecting and caring for children and grandchildren.

The researchers suspect that the menopause, which the whales experience in their 30s or 40s, is related to the animals' social structure.

"Killer whales have a very unusual social system whereby sons and daughters don't disperse from their social group but instead live with their mother her entire life. As a female ages she shares more genes with group members, and theory predicts that older females can benefit more from helping their offspring and grand offspring than reproducing themselves," says Dr Darren Croft of the University of Exeter a lead investigator on the study.

"The situation with killer whales is quite different to humans. When a killer whale couple reproduces, the male will go to another group to mate with a female there. But, unlike the human population, he will later return to the group where his mother is. So in whales we have different ideas for why older females maybe have more pressure to look after their offspring, and grand-offspring," says Dr Dan Franks of the University of York a lead investigator on the study.

To discover why the menopause developed in the whales, the team will use information collected over the last 30 years about two populations of killer whales with over 550 individuals between them. The unique dataset includes birth and death dates as well as more complex data, like the genetic and social relationships between the different animals.

From preliminary work the scientists expect to show that having a female around who no longer reproduces greatly increases the chances of children and grandchildren surviving.

In addition to the benefits to children and grandchildren, theory predicts that competition over resources may also have contributed to the evolution of menopause.

"There is often a conflict over resources between offspring of different generations," Franks says. "If an older female gives birth at the same time as one of her daughters then the two calves will be in competition. Theory predicts that the calves of the older mother should lose out in this competition. So it makes sense for the older female to give up her reproductive rights and instead help raise the younger generation's offspring."

They will then look at how a female who has undergone menopause helps offspring survive. They suspect it is because older females take a leadership role in the social group and have more knowledge on where and when food is available.

While human menopause is fairly well understood, the scientists hope to be able to assess their findings against the human menopause and provide greater insight into this unusual animal trait.

"I wouldn't be surprised if through this project we learn more about the evolution of human menopause. Much of what we're proposing is inspired by research on human menopause, and we expect our research to lead to new ideas that will allow us to ask more questions about human evolution." says Franks.


Further information

NERC media office
01793 411561
07917 557215

Harriet Jarlett
01793 411939
07785 459139


Notes

1. NERC is the largest funder of environmental science in the UK. We invest £330 million in cutting-edge research, training and knowledge transfer in the environmental sciences. Our scientists study and monitor the whole planet, from pole to pole, and from the deep Earth and oceans to the edge of space. We address and respond to critical issues such as environmental hazards, resource security and environmental change. Through collaboration with other science disciplines, with UK business and with policymakers, we make sure our knowledge and skills support sustainable economic growth and public wellbeing - reducing risks to health, infrastructure, supply chains and our changing environment.

2. Dr Dan Franks, of the Department of Biology at the University of York is a member of York Centre for Complex Systems Analysis (YCCSA) - external link. YCCSA is a community of researchers drawn from different departments developing novel mathematical, computational and analytical methods and tools for the analysis and modelling of complex systems.

3. The Sunday Times University of the Year 2012-13, the University of Exeter - external link - is a Russell Group university and in the top 1% of institutions globally. It combines world-class research with very high levels of student satisfaction. Exeter has over 18,000 students and is ranked 8th in The Times and The Sunday Times Good University Guide league table, 10th in The Complete University Guide and 12th in the Guardian University Guide 2014. In the 2008 Research Assessment Exercise (RAE) 90% of the University's research was rated as being at internationally recognised levels and 16 of its 31 subjects are ranked in the top 10, with 27 subjects ranked in the top 20.
The University has invested strategically to deliver more than £350 million worth of new facilities across its campuses in the last few years; including landmark new student services centres - the Forum in Exeter and The Exchange on the Penryn Campus in Cornwall, together with world-class new facilities for Biosciences, the Business School and the Environment and Sustainability Institute. There are plans for another £330 million of investment between now and 2016.

Press release: 80/13