Menopause Helps Killer Whales To Stop Competing With Daughters

Menopause is not a common phenomenon in the animal world or even the world of mammals. Apart from humans, only short-finned pilot whales and killer whales are the only known mammals to experience it. Female orcas (or killer whales) stop reproducing at the age of 30 or 40 years just as women (human females) experience menopause at the age of 45 to 55 years.

According to the Inquisitr, most animals with long lifespans like elephants or blue whales keep giving birth until their old age and even when they are close to death. However, a group of scientists at the Pacific Northwest noted that one of the 24 whales they had been observing for the past four decades had not been sighted for the last three months.

This whale was named Granny and the project was named J-pod. The scientists pegged the age of Granny somewhere between 74 to 105 years. This killer whale intrigued the researchers as it never gave birth in the 40 years she was under observation.

In the study published in Current Biology, the authors wrote, "Why females of some species cease ovulation prior to the end of their natural lifespan is a long-standing evolutionary puzzle?" While the menopause may in-principle mean more fitness for older females, these benefits do not explain the timing when the menopause happens.

According to the researchers, in killer whales, older mothers who give birth at a similar time as their daughters are 1.67 times more likely to lose their children who are not yet 15 years old. It means that male killer whales venture out of their maternal pods to mate and then return to their mothers, while female orcas remain in their maternal pods at all times.

In the beginning, a female orca is less related to the makes in her local group as her father comes from a different social group. However, once she reproduces, her sons remain in her group and she becomes 'more related' to them.

When mother and daughter killer whales reproduce at a similar time, both try to feed their own respective offspring. Often, daughter killer whales are more capable of doing so. Scientists think that it is the strain of this competition is the reason behind the menopause of older killer whales.

The Cosmos magazine states that the menopause is an evolutionary anomaly. Darren Croft, the behavioral ecologist of the University of Exeter and the lead author of the study, believes that menopause in killer whales makes a perfect strategy for their evolution due to their unique social structure.

One another explanation that has been offered behind the menopause in older orcas earlier is that it happens so that grandmothers can assist mothers to bear their grandchildren. It means that the 'mother' killer whale stops reproducing so that she can help her daughter to look after her grandchildren.