Animal personality adds complexity to the processes of divergence between sympatric morphs of Arctic charr

Divergent selection is a powerful driver of speciation and has been widely studied in relation to the physical characters of organisms. Behavioural traits also significantly contribute to the evolutionary processes of divergence. However, studying such effects is fraught with difficulties as the development of behavioural traits is likely to be complex and is moulded by ontogenetic processes such as shifts in habitat use. Here we explored how several aspects of juvenile behavioural variation may relate to adaptive divergence in a freshwater fish. We assessed whether and how juveniles of two recently evolved, sympatric morphs of Arctic charr, Salvelinus alpinus, a small benthivorous and a planktivorous charr, show genetically based differences in personality that conform to their respective ecological niches, and whether these differences could contribute to reproductive isolation by generating maladaptive hybrid behaviours. Studying three aspects of behavioural variation (average trait value, consistent individual differences and trait correlations), we assessed the sociality and risk-taking propensity of hybrids and pure-morph offspring reared in common conditions. While no difference in average behavioural responses could be observed, the hybrids tended to show less repeatable behaviours and were not intermediate for behavioural syndromes that appear to differ between the two morphs. These results provide limited evidence of personality trait divergence among polymorphic fish, and suggest subtle, nonadditive effects of hybridization on the development of such traits.