The existence of animal personality (consistent individual differences in behaviours across contexts) and behavioural syndromes (correlations among personality traits) is intriguing, since one would expect that more flexible behaviour is selectively favoured. Understanding syndromes is therefore important. An excellent example is the migration syndrome found in many species. In many animal populations individuals differ considerably in their migration tendency. The extreme case is ‘partial migration,’ where only a fraction of the population migrates. Migrants often represent a non-random subset of the population that differ consistently in sets of phenotypic features (morphology, physiology, behaviour). Individual differences in this ‘migration syndrome’ are ideal to study the emergence of individual variation from both a mechanistic and an evolutionary perspective. By a combination of theoretical modelling and empirical studies, we will address the following questions:
- Under which conditions of spatiotemporal variation and predictability of the environment should we predict partial migration?
- Which factors determine differences in migration tendency between populations?
- Which individuals in a partially migrating population migrate and which individuals stay?
- When is the migration decision taken (early in development vs later in life) and by whom (the migrant itself vs parental effects)?
- What are the eco-evolutionary implications of partial migration?
We will use three-spined sticklebacks (Gasterosteus aculeatus) as our study system, because they inhabit ecologically diverse conditions, have populations exhibiting no, partial or full migration. In two field studies, encompassing a spectrum of populations and seasons, we will quantify the within- and between-population variation in migration tendency and the corresponding syndrome. In two lab experiments, we will investigate the emergence of the migration syndrome and possibility for parental programming. The empirical studies will be complemented by theoretical modelling to derive testable predictions and to provide a framework for interpreting the empirical results. Together this will provide a deeper understanding of three intriguing basic biological phenomena: individual differences, behavioural syndromes and partial migration.