Individuals within populations vary enormously in mortality risk and longevity, but the causes of this variation remain poorly understood. A potentially important and
phylogenetically widespread source of such variation is maternal age at breeding, which typically has negative effects on offspring longevity. Here, we show that paternal
age can affect offspring longevity as strongly as maternal age does, and that breeding age effects can interact over two generations in both matrilines and patrilines. We
manipulated maternal and paternal ages at breeding over two generations in the neriid fly Telostylinus angusticollis. To determine whether breeding age effects can be
modulated by the environment, we also manipulated larval diet and male competitive environment in the first generation. We found separate and interactive effects of
parental and grandparental ages at breeding on descendants’ mortality rate and lifespan in both matrilines and patrilines. These breeding age effects were not
modulated by grandparental larval diet quality or competitive environment. Our findings suggest that variation in maternal and paternal ages at breeding could contribute
substantially to intra-population variation in mortality and longevity.

This experiment was conducted using the neriid fly, Telostylinus angusticollis. We reared individuals of the grandparental (F1) generation on either a high-nutrient or low-nutrient larval diet and then allowed adult females and males from these larval diet treatments to breed at 15 and 35 days of age. Neriid males fight other males for access to territories and females, and such male-male interactions could affect male ageing. We therefore investigated the potential for male-male interactions to affect paternal age effects by manipulating F1 male competitive environment. Female and male offspring (F2) were reared on a standard larval diet (with a nutrient concentration intermediate between the high-nutrient and low-nutrient diets) and then allowed to breed at 15-day age intervals between ages 15 and 60 days. We quantified the adult longevity of grand-offspring (F3) and used these data to test for effects of grandparental ages at breeding, grandparental environment, and parental ages at breeding on grand-offspring lifespan, mortality rate, and actuarial ageing rate.

The data was processed using linear mixed effects modelling and BaSTA (Bayesian Survival Trajectory Analysis) to examine patterns of lifespan and mortality.

Analysis was conducted using R 3.3.2, the packages "lme4", "lmerTest","car", and "BaSTA."