Why do orcas experience menopause?

Orcas have a complex social organisation (Baird and Whitehead, 2000).

Menopause is rare (Ellis et al., 2018) and raises the question of the advantage of selection for survival after the cessation of reproduction (Williams, 2001).

Only few mammal species experience menopause: orcas (Orcinus orca), short-finned pilot whales (Globicephala macrorhynchus), narvals (Monodon monoceros), beluga whales (Delphinapterus leucas), false killer whales (Pseudorca crassidens), humans (Sapiens sapiens) and, as recent studies show, chimpanzees (Pan troglodytes) (Olesiuk et al., 1990; Wood et al., 2023).

Different hypothesis have been made to explain the occurrence of menopause for these species, as referenced by Van der Bles (2024), including evolutive advantage (e.g. grandmother hypothesis, cancer reduction) and non-evolutive hypothesis (e.g. follicular exhaustion). The menopause might be the result of the various hypothesis combined.

Killer whale populations have the longest recorded post-reproductive lifespan of all non-human animals: females generally stop reproducing in their 30s to 40s but can survive into their 90s (Cant and Johnstone, 2008; Johnstone and Cant, 2010; Olesiuk et al., 1990).

It has been proposed that unusual kinship dynamics have predisposed killer whales to evolve towards early reproductive cessation in response to intergenerational reproductive conflict (Cant and Johnstone, 2008; Johnstone and Cant, 2010). Under these conditions, theory predicts that females should cease reproduction when females from a younger generation start to reproduce (Cant and Johnstone, 2008).

The number of relatives in the group increases with female age up to the end of reproduction (Croft et al., 2017; Johnstone and Cant, 2010). Croft et al. (2017) shows that younger females investing more in competition are favoured and thus have greater reproductive success than older females (their mothers) when breeding at the same time, with the mortality hazard of calves from older-generation females being 1.7 times that of calves from younger-generation females.

Ellis et al. (2024) shows that menopause results in females increasing their opportunity for intergenerational help by increasing their lifespan overlap with their grandoffspring and offspring without increasing their reproductive overlap with their daughters (Nattrass et al., 2019). The grandmothers, possessing ecological knowledge can transfer it to the younger generations (Brent et al., 2015; Foster et al., 2012; Ward et al., 2009; Whitehead, 2015).

Post-reproductively aged females lead groups during collective movement in salmon foraging grounds, increasing the survival of their adult offspring and grandoffspring, with especially prominent benefits provided during difficult years when salmon abundance is low to moderate (Brent et al., 2015; Nattrass et al., 2019). For example, prior to parturition, females need resources to conceive and provision their gestating offspring, and after, killer whales need more food to support lactation (Williams et al., 2011). 

It has been shown that post-reproductive females are more likely to lead their sons than their daughters, increasing the survival of their adult sons in a number of ways, including assisting in foraging and providing support during agonistic encounters (Baird and Whitehead, 2000; Brent et al., 2015; Foster et al., 2012; Grimes et al., 2023). Male killer whales are impressive animals but seem to have challenging lives, with much higher mortality rates than their sisters (Foster et al., 2012), perhaps because their prey, the salmon, are relatively small. They stay with their mother, effectively doubling the society’s matrilineal nature, and are dependent on her and on what she knows (Brent et al., 2015; Whitehead, 2015).

Bibliography

Baird, R. W. and Whitehead, H.: Social organization of mammal-eating killer whales: group stability and dispersal patterns, 2000.

Brent, L. J. N., Franks, D. W., Foster, E. A., Balcomb, K. C., Cant, M. A., and Croft, D. P.: Ecological Knowledge, Leadership, and the Evolution of Menopause in Killer Whales, Current Biology, 25, 746–750, https://doi.org/10.1016/j.cub.2015.01.037, 2015.

Cant, M. A. and Johnstone, R. A.: Reproductive conflict and the separation of reproductive generations in humans, Proc. Natl. Acad. Sci. U.S.A., 105, 5332–5336, https://doi.org/10.1073/pnas.0711911105, 2008.

Croft, D. P., Johnstone, R. A., Ellis, S., Nattrass, S., Franks, D. W., Brent, L. J. N., Mazzi, S., Balcomb, K. C., Ford, J. K. B., and Cant, M. A.: Reproductive Conflict and the Evolution of Menopause in Killer Whales, Current Biology, 27, 298–304, https://doi.org/10.1016/j.cub.2016.12.015, 2017.

Ellis, S., Franks, D. W., Nattrass, S., Cant, M. A., Bradley, D. L., Giles, D., Balcomb, K. C., and Croft, D. P.: Postreproductive lifespans are rare in mammals, Ecology and Evolution, 8, 2482–2494, https://doi.org/10.1002/ece3.3856, 2018.

Ellis, S., Franks, D. W., Nielsen, M. L. K., Weiss, M. N., and Croft, D. P.: The evolution of menopause in toothed whales, Nature, 627, 579–585, https://doi.org/10.1038/s41586-024-07159-9, 2024.

Foster, E. A., Franks, D. W., Mazzi, S., Darden, S. K., Balcomb, K. C., Ford, J. K. B., and Croft, D. P.: Adaptive Prolonged Postreproductive Life Span in Killer Whales, Science, 337, 1313–1313, https://doi.org/10.1126/science.1224198, 2012.

Grimes, C., Brent, L. J. N., Ellis, S., Weiss, M. N., Franks, D. W., Ellifrit, D. K., and Croft, D. P.: Postreproductive female killer whales reduce socially inflicted injuries in their male offspring, Current Biology, 33, 3250-3256.e4, https://doi.org/10.1016/j.cub.2023.06.039, 2023.

Johnstone, R. A. and Cant, M. A.: The evolution of menopause in cetaceans and humans: the role of demography, Proc. R. Soc. B., 277, 3765–3771, https://doi.org/10.1098/rspb.2010.0988, 2010.

Nattrass, S., Croft, D. P., Ellis, S., Cant, M. A., Weiss, M. N., Wright, B. M., Stredulinsky, E., Doniol-Valcroze, T., Ford, J. K. B., Balcomb, K. C., and Franks, D. W.: Postreproductive killer whale grandmothers improve the survival of their grandoffspring, Proc. Natl. Acad. Sci. U.S.A., 116, 26669–26673, https://doi.org/10.1073/pnas.1903844116, 2019.

Olesiuk, P. F., Bigg, M. A., and Ellis, G. M.: Life history and population dynamics of resident killer whales (Orcinus orca) in the coastal waters of British Columbia and Washington State., Report of the International Whaling Commission, 12, p 209-243, 1990.

Van der Bles, T. J.: Understanding the occurrence of menopause and post reproductive lifespans, Bachelors’ thesis Life Sciences, 2024.

Ward, E. J., Parsons, K., Holmes, E. E., Balcomb, K. C., and Ford, J. K.: The role of menopause and reproductive senescence in a long-lived social mammal, Front Zool, 6, 4, https://doi.org/10.1186/1742-9994-6-4, 2009.

Whitehead, H.: Life History Evolution: What Does a Menopausal Killer Whale Do?, Current Biology, 25, R225–R227, https://doi.org/10.1016/j.cub.2015.02.002, 2015.

Williams, G. C.: Pleiotropy, Natural Selection, and the Evolution of Senescence : Evolution 11, 398-411 (1957)., Sci. Aging Knowl. Environ., 2001, cp13–cp13, https://doi.org/10.1126/sageke.2001.1.cp13, 2001.

Williams, R., Krkošek, M., Ashe, E., Branch, T. A., Clark, S., Hammond, P. S., Hoyt, E., Noren, D. P., Rosen, D., and Winship, A.: Competing Conservation Objectives for Predators and Prey: Estimating Killer Whale Prey Requirements for Chinook Salmon, PLoS ONE, 6, e26738, https://doi.org/10.1371/journal.pone.0026738, 2011.

Wood, B. M., Negrey, J. D., Brown, J. L., Deschner, T., Thompson, M. E., Gunter, S., Mitani, J. C., Watts, D. P., and Langergraber, K. E.: Demographic and hormonal evidence for menopause in wild chimpanzees, Science, 382, eadd5473, https://doi.org/10.1126/science.add5473, 2023.

April 2025

Legal notices / Mentions légales