Parental diet has strong transgenerational effects on offspring immunity

1. Transgenerational effects of immune stimulation on offspring immunity are widely reported from insects, but we know very little of how other aspects of the parental environment affect offspring immune reactivity. 2. We reared male and female moths Plodia interpunctella on either good- or poor-quality food and then also raised their offspring on one of the two diet qualities. We found strong transgenerational effects on immunity: in general, if only one parent received the poor diet, reductions in immunity were observed whether that parent was the mother or the father, and the lowest offspring immune reactivity was observed when both parents received the poor diet. 3. The mechanism behind these effects is not known, but they could be caused either by imprinting, whereby the parent gives the offspring a cue such as an epigenetic mark that changes the offspring phenotype, or by the mother allocating fewer resources to their offspring when the diet was poor. Two lines of evidence point towards imprinting: the strong paternal effects and the observation that the size of these effects was either unchanged or increased when the offspring were fed a good-quality diet themselves. 4. Weight was also reduced when either parent was fed a poor diet, except when both parents had a poor diet and the offspring were raised on good food, contrasting with the increased rates of obesity seen in vertebrates when either parent is raised on a restricted diet. 5. Overall, the effects of parental diet on offspring weight and immune reactivity are substantial and in some cases are equivalent to that of the diet that the offspring itself consumes.