A family history: Effects of parental age on offspring life-history traits in bighorn sheep

Long-term fitness effects of parental age could affect population
dynamics, as age structure can vary considerably over time. Few studies of
wild animals, however, have examined the possible long-term fitness
consequences of parental age. Based upon 50 years of data on wild bighorn
sheep, we investigated how parental age affected three offspring traits –
mass at three years, longevity, and female lifetime reproductive success.
We also tested for a survival filter which could mask or increase fitness
effects of parental age. Our results showed a significant, quadratic
negative association between maternal age, offspring longevity and female
lifetime reproductive success. Offspring born to mothers aged 5-6 years
lived about 2 years longer and weaned about 1.5 lambs more than siblings
born to mothers aged 12-13 years. The effect of paternal age was not
significant. There was also a positive association between the longevity
of mothers and offspring. We did not detect any effects of parental age on
mass at three years for offspring of either sex. These results demonstrate
the presence of persistent maternal age effects in a long-lived species.
The sex-specific effects support the importance of analyzing maternal and
paternal age effects separately, as well as effects on female and male
offspring. This study advances our understanding of evolutionary processes
and population dynamics in wild long-lived mammals.