The environment experienced early in life shapes the phenotype for a lifetime and may even affect subsequent generations. Phenotypic effects generated by early environmental influences include alterations in key life history traits and major behavioural strategies. The underlying phenotypic plasticity is assumed to be under selection. The adaptive value of such developmental plasticity is surprisingly little understood. A key problem hampering our understanding of the significance of developmental plasticity in animals is that experiments usually target only a single environmental variable and/or a single ontogenetic period. However, in nature the development of well-integrated phenotypes occurs under the influence of multiple environmental factors and during a succession of ontogenetic stages. Lake Tanganyika cichlids provide unique models to study the development of integrated phenotypes due to their behavioural and social complexity, and their amenability to experimental manipulation. In these species, experiments in semi-natural conditions can be combined with detailed ecological knowledge to understand the functional significance and the underlying mechanisms of developmental plasticity. Here we present experimental results from maternal mouthbrooders (Simochromis pleurospilus) and cooperatively breeding cichlids (Neolamprologus pulcher) showing that (i) maternal effects seem to target only those phases of offspring life when they actually promote survival, but are abolished after this 'profitable period'¹, (ii) maternal effects on behaviour and brain architecture can be fully reversed by direct early experience of offspring², and (iii) early experience of multiple ecological factors can result in interacting reaction norms; the latter result suggests that organisms require information on multiple environmental factors in order to express adequate plastic responses. In general, our results suggest that developmental experiments must reflect biologically relevant, environmental variation if aiming to understand evolved reaction norms.