Sex-dependent effects of parental age on offspring fitness in a cooperatively breeding bird

Abstract

Parental age can have considerable effects on offspring phenotypes and health. However, intergenerational effects may also have longer-term effects on offspring fitness. Few studies have investigated parental age effects on offspring fitness in natural populations while also testing for sex- and environment-specific effects. Further, longitudinal parental age effects may be masked by population-level processes such as the selective disappearance of poor quality individuals. Here, we used multi-generational data collected on individually marked Seychelles warblers (Acrocephalus sechellensis) to investigate the impact of maternal and paternal age on offspring lifespan and lifetime reproductive success. We found negative effects of maternal age on female offspring lifespan and lifetime reproductive success which was likely driven by within-mother effects. There was no difference in annual reproductive output of females born to older versus younger mothers, suggesting that the differences in offspring lifetime reproductive success are driven by offspring lifespan. In contrast, the lifetime reproductive success of male offspring increased with maternal age, but this was driven by between-mother effects. No within- or between-individual paternal age effects were found for female offspring, but fathers that reached old age produced male offspring with higher lifetime reproductive success. We did not find strong evidence for environment-dependent parental age effects. Our study provides evidence for parental age effects on the lifetime fitness of offspring and shows that such effects can be sex-dependent. These results add to the growing literature indicating the importance of intergenerational effects on long-term offspring performance and highlights that these effects can be an important driver of variation in longevity and fitness in the wild.