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Reproductive Conflict and the Evolution of Menopause in Killer Whales.

Published version
Peer-reviewed

Type

Article

Change log

Authors

Johnstone, Rufus A 
Ellis, Samuel 
Nattrass, Stuart 
Franks, Daniel W 

Abstract

Why females of some species cease ovulation prior to the end of their natural lifespan is a long-standing evolutionary puzzle [1-4]. The fitness benefits of post-reproductive helping could in principle select for menopause [1, 2, 5], but the magnitude of these benefits appears insufficient to explain the timing of menopause [6-8]. Recent theory suggests that the cost of inter-generational reproductive conflict between younger and older females of the same social unit is a critical missing term in classical inclusive fitness calculations (the "reproductive conflict hypothesis" [6, 9]). Using a unique long-term dataset on wild resident killer whales, where females can live decades after their final parturition, we provide the first test of this hypothesis in a non-human animal. First, we confirm previous theoretical predictions that local relatedness increases with female age up to the end of reproduction. Second, we construct a new evolutionary model and show that given these kinship dynamics, selection will favor younger females that invest more in competition, and thus have greater reproductive success, than older females (their mothers) when breeding at the same time. Third, we test this prediction using 43 years of individual-based demographic data in resident killer whales and show that when mothers and daughters co-breed, the mortality hazard of calves from older-generation females is 1.7 times that of calves from younger-generation females. Intergenerational conflict combined with the known benefits conveyed to kin by post-reproductive females can explain why killer whales have evolved the longest post-reproductive lifespan of all non-human animals.

Description

Keywords

cetacean, cooperation, fertility, grandmother hypothesis, human evolution, life history, senescence, Animals, Biological Evolution, Female, Menopause, Reproduction, Whale, Killer

Journal Title

Curr Biol

Conference Name

Journal ISSN

0960-9822
1879-0445

Volume Title

27

Publisher

Elsevier BV