In animals, behaviour allows fastest adaptive adjustment to environmental conditions. Nevertheless, even this trait is often constrained by heritability. This also applies to behavioural phenotypes often called "personality traits". Recent theoretical considerations postulate that individuals within a species will display different behavioural phenotypes that may be characterized as 'bold' or 'shy' when their life histories predictably differ. We want to test whether such evolved behavioural phenotypes exist and how they are adjusted to predictable seasonality despite heritability. We use the situation of small rodents that allocate all available resources to growth and reproduction when born into spring conditions predicting good, abundant food resources in the near future, whereas young born into autumn conditions will delay reproduction until the next spring and are thereby forced to maximize survival prohability over the long winter period. Using a medium-sized rodent, the cavy (Cavia aperea) we will test how behavioural phenotypes develop and adjust to predicted reproductive options when young are born into different photoperiods (increasing: spring; decreasing: autumn). In addition, in a potential second funding period, we will test how litter size and thereby early competitive environment influences the behavioural phenotype of individuals. This research will provide insights into the adjustment of behavioural traits by phenotypic plasticity to predictable environmental options and will determine whether such ontogeneticallly canalized traits remain stable over an individual's life time.