Whale menopausal woes

IS the menopause confined to humans?

Does no other animal experience the dreaded hot flushes? Not quite.

Female killer whales can live to be 90 but they stop having babies in their forties. Non-reproductive individuals are a drain on the resources of a community and natural selection usually ensures they are shown the door.

However, redundant killer whales, and ladies past their sell-by date, are allowed to survive.

Why? In the case of humans, the role of the menopause is fairly clear. Our species depends on knowledge and know-how for its survival. A child needs 12 to 15 years of nurture before it’s able to contribute to the community. A mother, therefore, must have a reasonable prospect of surviving at least that long when she embarks upon her final pregnancy. Getting on in years, she is better off giving her grandchildren a better start in life than having more babies of her own; hence the early shut-down of her reproductive system.

There’s another reason. In ‘the Ireland that we dreamed of..’, hoped Éamon de Valera, ‘firesides would be forums for the wisdom of serene old age’.

Prior to the invention of writing, old people were the filing cabinets of their communities, storing the accumulated wisdom of the tribe. They knew ‘where the bodies are buried’. In a precarious world of famines floods and plagues, their recollections could mean the difference between life and death.

Remembering which plants could be eaten in an emergency, or where water was found during a drought long ago, might save the day.

Whale pods have the cetacean equivalents of ‘athletic youths’ and ‘comely maidens’ but Dev’s fireside ‘seanchaí’ are not a whale thing. So what is their menopause all about? For Dr Darren Croft it’s ‘one of nature’s great mysteries’. He, and his team from the Universities of Exeter and York, have been trying to solve it.

Among mammals generally, maturing young males bid farewell to their parents and move away from home. Females, on the other hand, tend to stay closer to where they were brought up; separation of the siblings according to sex helps avoid incest. Orca males do things differently; both males and females remain in the natal pod, with their mothers and aunties, for life. ‘There’s a spot in my heart that no colleen may own’ is the killer whale anthem.

Males don’t breed with their sisters, however. Instead, they make one-night-stand sorties to other pods and find partners there. The behaviour ensures that new genes are introduced to a pod and that incest is avoided. But this doesn’t fully explain why orca males remain so attached to their mothers.

The huge dorsal fins of killer whales protrude from the water and are easily photographed. The shape of each fin is unique, the equivalent of a fingerprint. It’s relatively easy, therefore, for scientists to recognise individuals. Dr Croft’s team examined orca pictures taken over the last three and a half decades. They identified 589 individuals, 297 of which died during the study. When the team compared the survival records of mothers and sons they found something extraordinary; if a male orca’s mother dies, his survival prospects plummet.

A male over 30 years old, who loses his mother, has a 14 times greater chance of dying during the year following her death than a whale who isn’t orphaned. Somehow, having a mother to look out for him, is a godsend to a male orca. But how does she help her son? We know little about the behaviour of whales in pods. Dr Croft thinks that a mother assists her son by warding off aggressive rivals. Keeping other whales away when he is foraging ensures that he is fit and strong facing the trials of love and war.

Like a human granny, she helps propagate her own genes by investing in the welfare of her sons; a healthy vigorous male will secure more matings when he visits other pods, increasing the number of his mother’s grandchildren and ensuring the wide dispersal of her genes.

There’s a downside, however, for Mammy’s boy; he is likely to die as soon as she’s gone. While mothers may survive into their 90s, their sons die in their 50s. So it’s a case of ‘God bless you and keep you, Mother mo Croí’, with a vengeance!