A research conducted by several countries found that mother-daughter conflicts could be the reason why killer whales are one of the three mammal species that “suffer” the menopause condition.
The study was made with the collaboration of the Universities of Exeter, Cambridge and York (UK), the Center for Whale Research (USA) and Fisheries and Oceans Canada. The investigation was published Saturday in the Current Biology journal. A theory proposes that post-reproductive killer whales have a “grandmother” role within the animal group, which allows them to share vital information regarding where and when the related whales can find food, increasing the survival rate of the family.
The study was led by Professor Darren Croft of the University of Exeter. This exhaustive investigation allowed the scientists to determine that aged whales found difficulty when competing with their daughters when it comes to reproduction.
When analyzing the data, the scientists found that, when comparing both mother and daughter mortality at the time of the pregnancy, the mother whales had 1.7 times more chances of dying than younger specimens.
“Older females are more closely related to the family group than younger females. This imbalance in local relatedness between mothers and their own female offspring means that older females do best to invest more heavily in the wider family group whereas younger females should invest more in competition,” Croft explained when presenting the study.
‘A reproductive conflict’
Four decades studying the whale behavior in the Pacific Northwest was enough for researchers to reach to the conclusion that a reproductive conflict is a principal reason for killer whales developing menopause.
An earlier work performed by Professor Mike Cant, University of Exeter and Professor Rufus Johnstone, University of Cambridge, both co-authors of the new study, presented the theory that explained why the menopause condition was due to “generational conflicts” related to reproduction. This new study is the first to prove this thesis in non-human species.
“Our previous work shows how old females help but not why they stop reproducing,” said Professor Darren Croft. “Females of many species act as leaders in late life but continue to reproduce, but this new research shows that old females go through the menopause because they lose out in reproductive competition with their own daughters.”
Professor Cant said that he was pleased about a study confirming what he and his co-workers had anticipated seven years ago. He stated that not only the scientists have discovered the key that explains menopause, but also why post-reproductive and older specimens often live longer.
A co-author of the study and Doctor from the University of York in the U.K., Daniel Franks, stated that their new discoveries explain that if older whales wanted to reproduce along with their daughters, they would be “out-competed”. Added to this fact, Franks said, there is the time and effort investment that older whales made regarding family protection and feeding.
However, according to Dr. Cant, the “grandmother” theory is not strong enough to explain menopause itself. Cant explains that as the grandchildren of killer whales carry only one-quarter of the whale’s genes, it does not represent a sufficient reason for “ever favor stopping reproduction in the first place.”
Often, female whales start its reproductive cycle at the age of 15 and keep it until they turn 35. However, killer whales can live until 90 years old, which translates into two-thirds of their lives without being reproductively useful. Also, because younger whales are related to fewer male whales, they become more competitive and even can fight with other similar-aged whales.
The importance of data recollection
The scientific team studied over 200 whales specimens that lived in the North West Pacific Coast of Canada and in certain American zones. All the populations included several family groups that helped to the understanding of the behavior of every pod member.
One of the principal studied groups was the J-pod. Currently, this whale group includes 24 members that were led by J2 (the “grandmother”), which died this month. Before J2 passed away, she had been post-reproductive for at least 40 years, granting the investigation team with a lot of material to be analyzed.
According to Dr. Deborah Giles from the Center for Whale Research, J2 was the “wise elder” within the Southern Resident killer whale clan. Giles explained that her ability to gather the members of the pod was amazing. 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.
The team concluded that the menopause condition is not by any chance an accident. Croft stated that it is an evolved method oriented to the cooperation within whale family groups that hopes to avoid any reproductive conflicts. These findings are fundamental to understanding why killer whales have so efficient survival rates and also becomes essential as several populations that were under investigation are considered endangered species.
Source: Cell