Frustrative reward omission increases aggressive behaviour of inferior fighters.
Animals use aggressive behaviour to gain access to resources, and individuals adjust their behaviour relative to resource value and own resource holding potential (RHP). Normally, smaller individuals have inferior fighting abilities compared with larger conspecifics. Affective and cognitive processes can alter contest dynamics, but the interaction between such effects and that of differing RHPs has not been adjudged. We investigated effects of omission of expected reward (OER) on competing individuals with contrasting RHPs. Small and large rainbow trout (Oncorhynchus mykiss) were conditioned to associate a light with reward. Thereafter, the reward was omitted for half of the fish prior to a contest between individuals possessing a 36-40% difference in RHP. Small control individuals displayed submissive behaviour and virtually no aggression. By contrast, small OER individuals were more aggressive, and two out of 11 became socially dominant. Increased aggression in small OER individuals was accompanied by increased serotonin levels in the dorsomedial pallium (proposed amygdala homologue), but no changes in limbic dopamine neurochemistry were observed in OER-exposed individuals. The behavioural and physiological response to OER in fish indicates that frustration is an evolutionarily conserved affective state. Moreover, our results indicate that aggressive motivation to reward unpredictability affects low RHP individuals strongest.
Department of Animal and Aquacultural Sciences, Norwegian University of Life Sciences, , PO Box 5003, Ås 1432, Norway, Department of Biosciences, University of Oslo, , PO Box 1041, Blindern, Oslo 0316, Norway, Faculty of Veterinary Medicine, University of Veterinary and Pharmaceutical Sciences, , Palackého tř. 1/3, Brno 61242 , Czech Republic, Department of Marine Ecology and Aquaculture, Danish Institute for Fisheries Research, North Sea Centre, , PO Box 101, Hirtshals 9850, Denmark.
Marco A
MA
Vindas
Ida B
IB
Johansen
Sergio
S
Vela-Avitua
Karoline Sletbak
KS
Nørstrud
Marion
M
Aalgaard
Bjarne O
BO
Braastad
Erik
E
Höglund
Øyvind
Ø
Øverli
D000374:Aggression; D000818:Animals; D054022:Cerebrum / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D003213:Conditioning, Psychological; D004298:Dopamine / Q000378:metabolism*; D017686:Oncorhynchus mykiss / Q000502:physiology*; D012201:Reward; D012701:Serotonin / Q000378:metabolism*
D012701:Serotonin; D004298:Dopamine
aggression; dyadic contests; emotions; frustration; serotonin; trace conditioning