Fe­male bel­uga whales and nar­whals un­dergo the menopause, bring­ing the to­tal num­ber of species known to do so to five

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Menopause is rare in the an­i­mal king­dom. While many species may be less likely to re­pro­duce as they near the end of their life, un­til now only three an­i­mals were known to have an ‘evolved strat­egy’ where fe­males have a sig­nif­i­cant post-re­pro­duc­tive life­span: hu­mans, killer whales and short-finned pi­lot whales. But now researchers at the Univer­sity of Ex­eter and the Univer­sity of York have added two more toothed whale species to that list: bel­u­gas and nar­whals.

The team stud­ied dead whales from 16 species and found dor­mant ovaries in older bel­uga and nar­whal fe­males, in­di­cat­ing that they had gone through the menopause. The find­ing sug­gests that these species are likely to have so­cial struc­tures that in­volve fe­male bel­uga whales and nar­whals liv­ing among a greater num­ber of close rel­a­tives as they age.

“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 Dr Sam El­lis, of the Univer­sity of Ex­eter. “In killer whales, the rea­son to stop [re­pro­duc­ing] comes be­cause both male and fe­male off­spring stay with their moth­ers for life, so as a fe­male ages her group con­tains more of her chil­dren and grand­chil­dren. This in­creas­ing re­lat­ed­ness means that, if she keeps hav­ing young, they’re com­pet­ing with her own di­rect de­scen­dants for re­sources such as food. The rea­son to con­tinue liv­ing is that older fe­males can be of great ben­e­fit to their off­spring and grand-off­spring. For ex­am­ple, their knowl­edge of where to find food helps the group as a whole sur­vive.”

Stud­ies of an­ces­tral hu­man re­mains sug­gests they had sim­i­lar so­cial struc­tures, which may ex­plain why menopause has evolved in our own species, the researchers say. “Look­ing at other species like these toothed whales can help us es­tab­lish how this un­usual re­pro­duc­tive strat­egy has evolved,” said Prof Dar­ren Croft, also of the Univer­sity of Ex­eter.

Bel­uga whales live in Arc­tic waters, as do their close rel­a­tives the nar­whals

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