title: 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.
authors.affiliation: Centre for Research in Animal Behaviour, College of Life and Environmental Sciences, University of Exeter, Exeter EX4 4QG, UK.
authors.forename: Lauren J N
authors.initials: LJN
authors.lastname: Brent
authors.affiliation: Department of Biology and Department of Computer Science, University of York, York YO10 5DD, UK.
authors.forename: Daniel W
authors.initials: DW
authors.lastname: Franks
authors.affiliation: Centre for Research in Animal Behaviour, College of Life and Environmental Sciences, University of Exeter, Exeter EX4 4QG, UK.
authors.forename: Emma A
authors.initials: EA
authors.lastname: Foster
authors.affiliation: Center for Whale Research, 355 Smugglers Cove Road, Friday Harbor, WA 98250, USA.
authors.forename: Kenneth C
authors.initials: KC
authors.lastname: Balcomb
authors.affiliation: Centre for Ecology and Conservation, University of Exeter, Cornwall Campus, Penryn, Cornwall TR10 9EZ, UK.
authors.forename: Michael A
authors.initials: MA
authors.lastname: Cant
authors.affiliation: Centre for Research in Animal Behaviour, College of Life and Environmental Sciences, University of Exeter, Exeter EX4 4QG, UK. Electronic address: d.p.croft@exeter.ac.uk.
authors.forename: Darren P
authors.initials: DP
authors.lastname: Croft
mesh_terms: D000818:Animals; D001522:Behavior, Animal / Q000502:physiology; D005075:Biological Evolution; D004032:Diet; D017753:Ecosystem; D005247:Feeding Behavior / Q000502:physiology; D005260:Female; D006801:Humans; D007858:Learning; D008297:Male; D008593:Menopause / Q000502:physiology* / Q000523:psychology*; D008954:Models, Biological; D012474:Salmon; D012919:Social Behavior; D050685:Whale, Killer / Q000502:physiology* / Q000523:psychology*