A comparison of sex-specific senescence patterns in a long-lived marine mammal

The lifetime fitness of an individual is determined by the integrated
results of survival and reproduction. Improving our understanding of
variation in survival senescence within and between species will therefore
provide greater insight into the evolution of different life history
strategies. Survival is influenced by multiple factors, consequently,
variation in patterns of senescence is expected between individuals and
sexes and across mating systems and the continuum of life history
strategies. To date there is little consensus regarding the mechanisms
driving the evolution of sex differences in actuarial senescence,
necessitating the need for studies of sex-specific senescence for species
across a wide range of life histories. Here we used 37 years of data for
1,879 female and 1,474 male Weddell seals from Erebus Bay, Antarctica, to
estimate and compare sex-specific patterns of survival rates using basis
splines which allow flexible modeling of age-specific patterns. The
Weddell seal is a species of long-lived mammal that displays moderate
polygyny and little sexual size dimorphism, which makes it an unusual
species compared to other long-lived mammals that share the polygynous
mating system. We found that males had lower rates of survival throughout
life and higher rates of actuarial senescence after early adulthood
compared to females. These results add to our understanding of
sex-specific survival rates in the species and contribute information for
a long-lived, polygynous species that should aid in achieving a broader
understanding of aging between sexes and across the tree of life.