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Behavioural and neuroendocrine effects of environmental background colour and social interaction in Arctic charr (Salvelinus alpinus)

Erik Höglund¹, Paul H. M. Balm² and Svante Winberg^3,4,*

¹ Evolutionary Biology Centre, Department of Limnology, Uppsala University, Norbyvägen 20, SE-752 36 Uppsala, Sweden
² Department of Animal Physiology, Faculty of Science, University of Nijmegen, Toernooiveld 1, 6526 ED Nijmegen, The Netherlands
³ Evolutionary Biology Centre, Department of Animal Development and Genetics, Uppsala University, Norbyvägen 18A, SE-752 36 Uppsala, Sweden
⁴ Evolutionary Biology Centre, Department of Comparative Physiology, Uppsala University, Norbyvägen 18A, SE-75236 Uppsala, Sweden

View larger version (15K): [in a new window]   Fig. 1. The number of aggressive acts performed during each daily observation session (A) and the total number of aggressive acts (B) performed during four daily 5 min observation sessions by the socially dominant fish during social interaction in size-matched pairs of Arctic charr interacting on white or black backgrounds. Values are means ± S.E.M., N=7 pairs on a white and N=7 pairs on a black background. Different letters indicate a significant difference (P<0.05; Mann—Whitney U-test).

View larger version (15K): [in a new window]   Fig. 2. Skin darkness of socially dominant and subordinate Arctic charr allowed to interact in pairs on a white (N=7) or black (N=7) background. Skin darkness was measured on a linear grey scale, where 0 is white and 255 is black, 24 h before (white bars) and after 5 days (black bars) of social interaction. Controls are fish that were visually isolated on the white (N=8) or black (N=8) background. Values are means + S.E.M. Means with no common superscript letters are significantly different (P<0.05; Sheffé post hoc test).

View larger version (19K): [in a new window]   Fig. 3. Plasma concentrations of adrenocorticotropic hormone (ACTH) (A), -melanocyte-stimulating hormone (-MSH) (B) and cortisol (C) in socially dominant (N=7 for both black and white background) and subordinate (N=7 for both black and white background) Arctic charr after 5 days of social interaction in pairs on white or black background colour. Controls are fish that were visually isolated on a white (N=8) or black (N=8) background. Values are means + S.E.M. There were no significant differences between individual means (P<0.05; MANOVA followed by the Sheffé post hoc test on the combined effect of social position and background colour). For MANOVA statistics see Table 1.