FOR 1232: Reduction of Phenotypic Plasticity in Behavior by Early Experience: Functional Consequences of an Adaptive Mechanism?
Zusammenfassung der Projektergebnisse
Our research has taken an evolutionary perspective and focused on the potential adaptive significance of early developmental influences on behaviour. We concentrated on the evolutionarily important question whether and how changes in behavioural traits in early ontogeny represent adaptive shaping of the phenotype in response to specific predictable environmental influences rather than pathological aberrations. While the latter interpretation has been prevalent particularly in medical research, our research revealed clear evidence that adaptive shaping takes place. Pronounced effects of early conditions on shaping of behaviours were obvious, even independent of genetic variance as shown in our studies on isogenic mice. Guinea pigs and cavies express behavioural and endocrinological traits that are clearly adjusted to their environments during pregnancy and rearing. Adjustments were detectable to social conditions in guinea pigs and as adaptations to photoperiod in life history traits and connected behavioral traits in cavies. Similar adjustments to the social environment during early post-fledging ontogeny were observed in zebra finches. We found pregnancy and adolescence to be periods of particular importance for shaping behaviour. The strong effect of adolescence has been little investigated before but proved to be a period of potential major reorganisation. Even in invertebrates, we found influences of the early environment on later behavioural traits in beetles but also later plastic adjustments in the adult stage. We investigated the long-term consequences of such developmental shaping for the behaviour and fitness of adults under environmental conditions that either matched or mismatched the social and ecological conditions experienced early in life. Our findings suggest that the question of a strict reversibility of trait changes is less useful than the question whether changes can continue past the early ontogeny. Reversibility is unlikely given that neither the early ecological and social conditions are likely to repeat themselves nor is the state of the individual (size, age, social status and physiological condition) ever repeating. Our findings proved that animals across taxa show a much higher degree of phenotypic plasticity throughout life than previously assumed, allowing for readjustment of the behavioural phenotype, with potentially positive consequences on fitness. Explaining differences among behavioural phenotypes has been the main topic of personality research. However, this research has largely focused on differences among adults and neglected the developmental aspects of the behavioural phenotype. In this field, our research group has emphasized the importance of developmental processes at various stages of the life cycles beginning at the prenatal (vertebrates) or larval (invertebrates) stage, continuing to the early postnatal and adolescent period and including plasticity during adulthood. Our research has produced convincing examples of the ability of match-mismatch experiments to reveal the adaptive significance of developmental shaping and the importance of sensitive windows in behavioural development. Match-mismatch experiments proved particularly useful in documenting lasting effects of early developmental conditions, but also demonstrated that the stability of early effects varied between initial conditions. It also showed that early environments providing high quality resources led to offspring of overall superior quality, called a “silver spoon effect”. Thus, we did not always find the predicted negative effect of the mismatching conditions as we had initially predicted. The outcome of matchmismatch experiments should be interpreted with care as addressed by theoretical modelling. Our novel insights have been disseminated internationally through publications, workshops and special issues of international journals.
