Ecological Knowledge, Leadership, and the Evolution of Menopause in Killer Whales

Abstract

Classic life-history theory predicts that menopause should not occur because there should be no selection for survival after the cessation of reproduction [1]. Yet, human females routinely live 30 years after they have stopped reproducing [2]. Only two other species-killer whales (Orcinus orca) and short-finned pilot whales (Globicephala macrorhynchus) [3, 4]-have comparable postreproductive lifespans. In theory, menopause can evolve via inclusive fitness benefits [5, 6], but the mechanisms by which postreproductive females help their kin remain enigmatic. One hypothesis is that postreproductive females act as repositories of ecological knowledge and thereby buffer kin against environmental hardships [7, 8]. We provide the first test of this hypothesis using a unique long-term dataset on wild resident killer whales. We show three key results. First, postreproductively aged females lead groups during collective movement in salmon foraging grounds. Second, leadership by postreproductively aged females is especially prominent in difficult years when salmon abundance is low. This finding is critical because salmon abundance drives both mortality and reproductive success in resident killer whales [9, 10]. Third, females are more likely to lead their sons than they are to lead their daughters, supporting predictions of recent models [5] of the evolution of menopause based on kinship dynamics. Our results show that postreproductive females may boost the fitness of kin through the transfer of ecological knowledge. The value gained from the wisdom of elders can help explain why female resident killer whales and humans continue to live long after they have stopped reproducing.

A putative role for anti-Müllerian hormone (AMH) in optimising ovarian reserve expenditure

“…This is particularly true for humans, orca and short-finned pilot whales, all of which experience ovarian reserve depletion and menopause, many years before the end of their natural lifespan (Marsh & Kasuya 1986, Brent et al 2015, Depmann et al 2015. Menopause is rare throughout the animal kingdom, but increasing evidence suggests that reproductive senescence is common (Packer et al 1998, Nussey et al 2013.…”

Menopause Female Reproductive Senescence from the Viewpoint of Evolutionary Anthropology

“…Long postreproductive periods are uncommon among animals, even among large social mammals such as nonhuman primates and elephants. Only two Cetacean species such as short-inned pilot whales (Globicephala macrorhynchus) and killer whales (Orcinus orca) exhibit postreproductive life spans comparable to those of female Homo sapiens [22,26]. Female short inned pilot whales stop to reproduce by about 36 years of age but they can live up to 65 years [22].…”

Vocal Learning and Auditory-Vocal Feedback

“…Elephants and some toothed whales rival humans in having young dependent until their teenage years and with many adult females having a postreproductive period during which their reproductive effort is thought to be devoted to parental care (Marsh and Kasuya 1986 ;Tyack 1986;Lahdenperä et al 2014). These older females retain knowledge of great importance to their groups (McComb et al 2001;Brent et al 2015). This social setting in which the young are dependent for years during which they can learn valuable information from caregivers may provide selective pressures for the use of vocal learning to develop more open forms of communication.…”