The problem
Women and females of some toothed-whale species, including killer whales, can live for many years after reproduction ends. Why did evolution produce such a long later-life phase? Helping younger relatives and avoiding competition with them are possible parts of the explanation, but they do not yet explain every lineage.[1]
In humans and several toothed-whale species, females can live long after reproduction ceases. Why does this extended post-reproductive lifespan evolve in some lineages? A longer total lifespan and an earlier end to reproduction can produce a similar gap, so those possibilities must be distinguished.
Ellis and colleagues compared estimated total and reproductive lifespans among toothed-whale species. The pattern favored extending total life without a corresponding extension of reproductive life. Their demographic models estimated more time alive with grandchildren, without more time reproducing alongside daughters. This tests opportunities for help and reproductive conflict, rather than directly observing every benefit and cost.
A separate genome comparison identified unusually fast-changing DNA regions in killer whales, narwhals and belugas. Such accelerated regions are candidates for functional investigation; their association with this life history does not demonstrate that they cause menopause or were favored by selection.[1] [2]
Scope
Comparative explanation of extended female post-reproductive lifespan, including the roles of kin help, reproductive conflict and ecological conditions.
What remains open
Helping relatives and avoiding reproductive conflict have support, but do not yet explain every lineage.[1]
Why it matters
An older female can affect the success of relatives even without having more offspring herself. Studying menopause therefore connects lifespan to relationships between generations, and asks how the benefits of living longer can differ from those of reproducing longer.[1]
The same extra years can increase opportunities to help relatives while also increasing potential competition if reproduction continues. This makes menopause a way to test how social relationships influence the evolution of aging and reproduction, beyond counting one female’s offspring. Keeping demographic opportunities separate from demonstrated benefits, and genomic candidates separate from causal mechanisms, is essential to learning which explanations travel between lineages and which depend on a particular ecology.[1] [2]
Definitions
2 terms
Post-reproductive lifespan
The interval lived after reproduction has ended. This evolutionary question concerns an extended female later-life phase, not merely any individual surviving briefly after her last offspring.[1] [2]
Kin selection
Evolutionary change influenced by effects on relatives’ survival or reproduction, because relatives share inherited variants. Helping relatives is one possible contribution to menopause explanations, not a sufficient explanation of every lineage.[1]
Sources
- The evolution of menopause in toothed whales
Notes on The evolution of menopause in toothed whales
Comparative whale models support longer total life without matching reproductive extension. Estimated opportunities for help and conflict do not demonstrate every benefit or all-lineage causal sufficiency.
- Identification of accelerated regions associated with extended post-reproductive lifespan in toothed whales
Notes on Identification of accelerated regions associated with extended post-reproductive lifespan in toothed whales
Identifies candidate accelerated DNA regions in three whale species. Restricted taxa and projected annotations limit inference; causal regulation, positive selection and menopause causation are not demonstrated.