Mortality rate acceleration and post-reproductive lifespan in matrilineal whale species

Abstract

The strength of selection to increase the span of a life stage is dependent upon individuals at that stage being able to contribute towards individual fitness and the probability of their surviving to that stage. Complete reproductive cessation and a long post-reproductive female lifespan as found in humans are also found in killer whale (Orcinus orca) and short-finned pilot whale (Globicephala macrorhynchus), but not in the long-finned pilot whale (Globicephala melaena). Each species forms kin-based, stable matrilineal groups and exhibits kin-directed behaviours that could increase inclusive fitness. Here, the initial mortality rate and mortality rate-doubling time of females of these three closely related whale species are compared. The initial mortality rate shows little variation among pilot whale species; however mortality rate accelerates almost twice as fast in the long-finned pilot whale as it does in killer whale and short-finned pilot whale. Selection for a long post-reproductive female lifespan in matrilineal whales may therefore be determined by the proportion of females surviving past the point of reproductive cessation.

Learning, menopause, and the human adaptive complex

“…For example, there is a growing corpus of data on whales that should allow for comparative tests. Some toothed‐whales show clear evidence of menopause and a long postmenopausal lifespan in females 29,43 . It is interesting to note that this branch of the cetacean line shows some broad similarities in its foraging niche to humans.…”

“…Even in those toothed whales that evidence female menopause, there is no such equivalent in males. In those species, males typically have much shorter lifespans than females and do not invest in offspring 29 . Humans are an outlier species in many senses, from brain size to lifespan to menopause to male parental investment.…”

Senescence in natural populations of animals: Widespread evidence and its implications for bio-gerontology

“…Evidence for uncoupling of patterns of survival and fecundity senescence remain quite scarce. In females, post-reproductive survival has been documented in wild mammals, but with the possible exception of some toothed whales, this seems more likely the product of chance than some adaptive reproductive cessation (Cohen, 2004; Packer et al, 1998; Thompson et al, 2007; Foote, 2008; Ward et al, 2009). There is also some evidence from wild female ungulates that fecundity senescence may begin later and progress more rapidly than age-related declines in survival probability (Bérubé et al, 1999; Catchpole et al, 2004; Jorgenson et al, 1997; Nussey et al, 2009).…”

A Theory for the Origin of Human Menopause

“…If menopause is considered quantitatively on the basis of life history as a proportionately long time in adulthood during which individuals are non-reproductive (a “post-fertile life stage” sensu Levitis et al, 2013; Stone, 2013), then it indeed is remarkable in humans relative to other species in the animal kingdom (Alberts et al, 2013), occurring also only in killer whales (Brent et al, 2015; Franks et al, 2016) and perhaps short-finned pilot whales (Foote, 2008). We think that the ‘triumvirate hypothesis approach’ inherent in the theory might be applicable to explaining claims for menopause in other organisms, in which it is less conspicuous (Brody et al, 1923; Laws et al, 1975; Gosden et al, 1983; Kidd and Tozer, 1985; Nelson and Felicio, 1985; Marsh and Kasuya, 1986; Ottinger and Balthazart, 1986; Finch, 1990; Austad, 1993; von Saal et al, 1994; Packer et al, 1998; Holmes and Ottinger, 2003; Cohen, 2004; Goranson et al, 2005; McAuliffe and Whitehead, 2005; Minois et al, 2005; Reznick et al, 2006; Singh and Singh, 2006; Chen et al, 2007; Foote, 2008; Walker and Herndon, 2008; Atsalis and Videan, 2009; Ward et al, 2009). Alternatively, a similar synthetic approach but differing in details (e.g., hypotheses) may be required to address specific differences between humans and other organisms.…”