Born with an advantage: Early life and maternal effects on fitness in Columbian ground squirrels

Lifetime fitness and its determinants are an important topic in the study
of behavioural ecology and life-history evolution. Early life conditions
comprise some of these determinants, warranting further investigation into
their impact. In humans, for example, babies born lighter tend to have
lower life expectancy and fewer offspring than heavier ones. Similarly,
some of these life-history traits are passed on to offspring, with
lighter-born females giving birth to lighter offspring. We investigated
how weight at weaning, the relative timing of birth in the season,
maternal weight, and maternal age affected the longevity and lifetime
reproductive success (LRS) of female Columbian ground squirrels
(Urocitellus columbianus). We hypothesized that early life conditions such
as offspring weight would not only have lifetime fitness consequences but
also intergenerational effects. We found that weight at weaning had a
significant impact on longevity, with heavier individuals living longer.
The relative timing of an individual’s birth did not have a significant
association with either longevity or LRS. Individuals born to heavier
mothers were found to have significantly higher LRS than those born to
lighter mothers. Finally, maternal age was found to be significantly
associated with their offspring’s LRS, with older mothers having less
successful offspring. The latter finding may be due to an increased
success of offspring reproductive success when their mother is still
present. Our results provide evidence that early life conditions do have
lifelong fitness and sometimes intergenerational consequences for
Columbian ground squirrels. Keywords: maternal effects, longevity,
lifetime reproductive success, early life conditions, Columbian ground
squirrel.