Killer Whales And The Menopause

In the freezing cold waters off the coast of Canada, tall black fins slide effortlessly through the waves. The sound of tail and fin slapping echoes as the killer whales pass by, competing with the noise of camera shutters as buttons are pressed furiously, their owners desperate to capture such a magical moment. Every now and again, a head pops up as though the whales are watching the people as the people watch them. All of a sudden a whole body leaps through the waves and crashes back with a tremendous splash sending the camera shutters into a frantic blur. Gasping and cheering fills the air as the orcas head off for a day of hunting, feeding and socialising leaving only footprints on the surface and incredible memories in the minds of those watching.

Orcas are incredible animals and the chance to experience something like this is on many people’s bucket lists. Watching them swim so elegantly through the water, putting on fabulous acrobatic displays of power is awe inspiring and you might struggle to see what we have in common with them apart from being mammals. But, did you know, that we actually share something quite significant? The menopause.

The menopause is an evolutionary and biological condition experienced by females. It marks the end of their reproduction and occurs when the ovaries stop releasing eggs each month and menstruation ceases. The question is, why does this happen in killer whales?

According to some people, the menopause is simply an accident in biology. It occurred at some stage during evolution and has simply not yet disappeared. Others, however, believe that there is considerable evidence to suggest that it is a trait that evolved for a particular reason. One of the most fascinating suggestions for this is the idea of the “granny effect”, a hypothesis first proposed in 1966. The “granny effect” suggests that in order to aid their genetic survival, older females no longer bear children and instead focus on helping to support and raise their grandchildren. By doing so they give further generations a higher chance of reaching adulthood and therefore a higher chance of the survival of their lineage. However, whilst useful in determining family dynamics and genetic success in killer whales, it does not explain why they cease reproduction completely.

A recently published study by an international research team led by Professor Darren Croft of the University of Exeter, reveals that it is the relationship mother killer whales have with their daughters that proves to be essential when determining why they go through the menopause. Croft and his team studied two pods of whales off the north west coast of the US and Canada and used data collected for 43 years by the Centre for Whale Research and Fisheries and Oceans Canada in order to discover why. They looked at killer whales who were approaching the menopause but were still breeding along with their daughters who were also breeding. It was found that the older females’ calves were 1.7 times more likely to die than their younger daughters’ calves. The older whales lose the calving competition.

So, as a result of coming last in the race of reproduction, it appears as though rather than putting themselves and the future of the pod at risk, the older whales cease breeding and focus upon their grandchildren instead. Yes, they may lose out on continuing their gene pool through their own young but their contribution is incredibly important when it comes to ensuring it survives through generations.

Croft’s study revealed that post-menopausal whales find themselves with a “grandmother” role in the pod, hence the “granny effect”. They are often the leaders of the pods, they are more likely to be than adult males, and are vital in ensuring their family’s survival. It is believed that they know where the best places to fish are, using accumulated knowledge. When the group is desperate to find food, they know exactly where to go. All in all, post-breeding whales are not “past it”, they are crucial.

The menopause is certainly no evolutionary mistake. This new research is not only important in learning more about how it evolved within killer whales, it is also fascinating in learning more about humans. We too continue to survive long after our reproduction cycle ends. We can also be said to take on more caring and “grandmotherly” roles within our family groups. Many tribes, much like the whales, rely on previous knowledge and experience to understand where to find food, places to avoid and how to live through natural events like floods. We have a lot more in common with killer whales than we think.

As the first test of mother/daughter conflict in a non human species, Croft and his team have significantly contributed to our understanding of this particular whale species and post reproduction. Although they are hoping to carry out further research into these relationships using drones, it is most definitely indispensable knowledge aiding our understanding of killer whale survival in an increasingly turbulent world.

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