Poor developmental conditions decrease adult body size and egg size, but not egg laying rate and survival throughout adulthood: A long-term experiment in a precocial bird.

The quality of the environment during individual development is generally considered to have long-lasting effects on performance in adulthood, but this is mainly based on observational studies that cannot pinpoint the causal pathways behind such long-term effects. In this study, we performed a randomized controlled trial to test for causal effects of a poor rearing diet on performance in growth, reproduction, and survival over the complete life course of female Japanese quail (Coturnix japonica). All individuals were housed under standardized conditions as adults to allow separating effects of the developmental environment from effects of the adult environment. The poor rearing diet led to a dramatically reduced growth, which delayed the onset of reproduction and resulted in a reduced body size throughout adulthood, as compared to a standard rearing diet. While there were no detectable effects on age-specific egg laying rate and survival, despite strong senescence in these fitness traits, females reared with the poor diet did lay smaller eggs. Hence, although there was no effect of the poor developmental environment on female laying rate and survival per se, the developmental environment of a mother did affect her adult size and the environment she provides for her offspring during embryonic development. We suggest that the effects on female adult size and egg size may cause 'silver spoon' effects in the wild, if larger size provides an advantage in competition over resources. However, we cannot rule out that smaller size would lead to lower food requirements, thereby acting as a 'predictive adaptive response' to a poor environment.