University of Exeter Research Unravels How Whales Hold The Key To Menopause
Jan 16 2017
Professor Croft joined scientists from Cambridge and York University, as well as from the Center for Whale Research in the US and Fisheries and Oceans Canada. The study was published in the journal Current Biology. Image credit: AP/Elaine Thompson. Darren Croft from the University of Exeter said, "Her longevity isn't the interesting thing; it's her life without a calf". This exhaustive investigation allowed the scientists to determine that aged whales found difficulty when competing with their daughters when it comes to reproduction. When females of two generations breed at the same time, the mortality of older mothers' offspring is 1.7 times that of younger mothers' offspring. In addition, it has been discovered that older female orcas play a particularly important leadership role in their family group.
Researchers from the University of Exeter have been conducting a study on killer whales and they have found out something that might hold the key why menopause occurs.
It's been previously predicted that conflict between generations could explain why the female of some species, like humans, go through menopause. In the 40-plus years scientists have observed J-pod, Granny has never given birth, meaning she has yet to reproduce since the first time she caught the attention of human observers.
A couple of orcas.
Croft, who has spent time in the Salish Sea on both sides of the border near Vancouver Island observing the animals, said scientists have long considered why killer whales who stop having calves in their 30s and 40s have lifespans into their 80s, 90s and beyond.
Out of all the mammal species in the world, only three are known to experience menopause: humans, short-finned pilot whales and killer whales.
Professor Cant said that he was pleased about a study confirming what he and his co-workers had anticipated seven years ago. It means that we've captured a key piece of the puzzle of post-reproductive life. "Our previous work shows older, post-reproductive females do help their offspring survive but that, on its own, does not explain why they stop reproducing", said Croft. Killer whales, male and female, tend to stay with their maternal pod; males actually go visit other pods to mate and then return to their own.
However, according to Dr. Based on the data, the reason why killer whales go through menstruation has something to do with female orcas' relationships with their daughters. So as a female killer whale gets older, she has more of her offspring around her and she becomes increasingly closely related to the rest of the group. Also, because younger whales are related to fewer male whales, they become more competitive and even can fight with other similar-aged whales.
The team tested this theory by looking at over four decades of data collected on 200 different whales. The populations included several pods, made up a several family groups. Currently, this whale group includes 24 members that were led by J2 (the "grandmother"), which died this month.
This point was backed by Deborah Giles, of the Center for Whale Research, who has been observing Granny and the J2 pod for years. She had an incredible ability to call the other whales to her by vigorously slapping her tail on the water. J2 just had to slap her tail on the water vigorously, and no matter the distance, the other whales would come immediately to the call.
"We simply don't know what the menopause is for these animals", said Croft.
The paper concludes that "The lower survival of calves from older generation mothers in reproductive conflict can not be explained due to a general effect of mother's age on offspring survival as we found no effect of mother's age on offspring survival to age 15 across all calves born during the study period". The findings help to explain factors that are driving the whales' survival and reproductive success, which is essential information given that the Southern Resident killer whales - one of the whale populations under study - is listed as endangered and at risk of extinction.