Sex differences in adult lifespan and aging rates of mortality across wild mammals

Abstract

In human populations, women consistently outlive men, which suggests profound biological foundations for sex differences in survival. Quantifying whether such sex differences are also pervasive in wild mammals is a crucial challenge in both evolutionary biology and biogerontology. Here, we compile demographic data from 134 mammal populations, encompassing 101 species, to show that the female's median lifespan is on average 18.6% longer than that of conspecific males, whereas in humans the female advantage is on average 7.8%. On the contrary, we do not find any consistent sex differences in aging rates. In addition, sex differences in median adult lifespan and aging rates are both highly variable across species. Our analyses suggest that the magnitude of sex differences in mammalian mortality patterns is likely shaped by local environmental conditions in interaction with the sex-specific costs of sexual selection.

Keywords: comparative analysis; life history; longevity; senescence; sexual selection.

Fig. 1.

Sex differences in adult lifespan across mammals. For a given population, the sex difference is measured as the ratio log[(Male adult lifespan)/(Female adult lifespan)]. Multiple bars for a given species represent estimates gathered from different populations. Orange bars correspond to longitudinal data, gray bars correspond to transversal data, and dark gray bars correspond to the human populations. The black dot corresponds to the overall effect for nonhuman mammals and is associated with its 95% credibility interval.

Fig. 2.

Frequency distribution of the magnitude of sex differences in rate of aging across mammals in the wild (A). The black dot corresponds to the overall effect for nonhuman mammals and is associated with its 95% credibility interval. Patterns of age-specific changes in mortality rate for three mammalian populations are displayed. For each population the mortality curve with the vertical line representing the median adult lifespan and the posterior distribution of the aging rate b₁ are given in red for females and in blue for males. The mortality hazard corresponds to the instantaneous rate of mortality. In the three populations, adult females live on average longer than adult males. However, (B) in Asian elephant, Elephas maximus (Myanmar population), females have a higher aging rate; (C) in yellow baboon, Papio cynocephalus (Amboseli National Park population), no difference in aging rates is observed; and (D) in red deer, Cervus elaphus (Isle of Rum population), males show a higher rate of aging than females.

Fig. 3.

Effect of SSD (A), hunting (hunted vs. nonhunted populations) (B), and data quality (longitudinal–high quality vs. transversal–low quality) (C) on sex differences in median adult lifespan across mammals. The horizontal gray and dash line corresponds to the absence of sex differences in median adult lifespan.