Menopausal whales are influential and informative leaders

http://www.eurekalert.org/pub_releases/2015-03/cp-mwa022615.php

Public Release: 5-Mar-2015
Cell Press

Menopause is a downright bizarre trait among animals. It's also rare. Outside of the human species, only the female members of two whale species outlive their reproductive lives in such a major way. Female killer whales typically become mothers between the ages of 12 and 40, but they can live for more than 90 years. By comparison, males of the species rarely make it past 50. Now, researchers reporting in the Cell Press journal Current Biology on March 5 have new evidence to explain why, evolutionarily speaking, these select female whales live so remarkably long.

Older individuals serve as key leaders, directing younger members of whale society, and especially their own sons, to the best spots for landing tasty meals of salmon. In so doing, older females help their kin to survive. This leadership role takes on special significance in difficult years when salmon are harder to come by.

The researchers say the discovery offers the first evidence that a benefit of prolonged life after reproduction is that post-reproductive individuals act as repositories of ecological knowledge.

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Post-reproductively aged females were especially strong group leaders in years when salmon availability was low.

The findings in whales suggest that the origin of menopause in humans may have a similar explanation, the researchers say.

"In humans, it has been suggested that menopause is simply an artefact of modern medicine and improved living conditions," says Darren Croft of the University of Exeter, senior author of the study. "However, mounting evidence suggests that menopause in humans is adaptive. In hunter-gatherers, one way that menopausal women help their relatives, and thus increase the transmission of their own genes, is by sharing food. Menopausal women may have also shared another key commodity: information."

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