Friday, 31 August 2018

Beluga whales and narwhals go through menopause


August 27, 2018, University of Exeter
Scientists have discovered that beluga whales and narwhals go through the menopause—taking the total number of species known to experience this to five.
Aside from humans, the species now known to experience menopauseare all toothed whales—belugas, narwhals, killer whales and short-finned pilot whales.
Almost all animals continue reproducing throughout their lives, and scientists have long been puzzled about why some have evolved to stop.
The new study, by the universities of Exeter and York and the Center for Whale Research, suggests menopause has evolved independently in three whale species (it may have evolved in a common ancestor of belugas and narwhals).
"For menopause to make sense in evolutionary terms, a species needs both a reason to stop reproducing and a reason to live on afterwards," said first author Dr. Sam Ellis, of the University of Exeter.
"In killer whales, the reason to stop comes because both male and female offspring stay with their mothers for life—so as a female ages, her group contains more and more of her children and grandchildren.
"This increasing relatedness means that, if she keeps having young, they compete with her own direct descendants for resources such as food.
"The reason to continue living is that older females are of great benefit to their offspring and grand-offspring. For example, their knowledge of where to find food helps groups survive."
The existence of menopause in killer whales is well documented due to more than four decades of detailed study.
Such information on the lives of belugas and narwhals is not available, but the study used data on dead whales from 16 species and found dormant ovaries in older beluga and narwhal females.


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