Persistent maternal age effects on male offspring fitness traits in a wild mammal population

Effects of parental age on juvenile survival are well documented, but whether parental age has long-term consequences for the fitness of surviving offspring remains poorly understood. This is particularly the case for polygynous mammals, where differential impacts on sons versus daughters are predicted. Here, we investigate the effects of maternal and paternal age on offspring first-year survival, longevity, lifetime reproduction, and annual reproduction in a wild Soay sheep population. We find that younger and older mothers produced offspring that were less likely to survive their first year than middle-aged mothers, and this effect was independent of offspring sex. However, among offspring that survived their first year, adult lifespan and lifetime reproductive success were only influenced by maternal age in sons and not in daughters. Increased adult reproductive success in sons of middle-aged mothers, compared to young and old mothers, was not driven by maternal age effects on offspring reproductive ageing patterns, but potentially by consistent effects on offspring average annual reproductive performance. There was weak evidence of a paternal age effect on offspring longevity but no effect on other offspring traits. Our study shows long-lasting, sex-dependent maternal age effects on offspring fitness traits in the wild, adding to the growing body of literature that highlights the potential importance of intergenerational effects in natural populations.