Rats Benefit from Winner and Loser Effects

The outcome of contests over resources such as territories, food, and mates is determined by resource holding power (RHP) and resource value (Parker 1974; Huntingford & Turner 1987). In addition, previous fighting experience strongly influences the odds of winning. Winner and loser effects denote the higher probability of a winner to win a subsequent encounter and the higher probability of a loser to lose a subsequent encounter, regardless of the identity of the opponent (Chase et al. 1994; Dugatkin 1997; Hsu & Wolf 1999). Both effects have been demonstrated across a broad range of taxa, including invertebrates and vertebrates (for reviews see Hsu et al. 2006; Rutte et al. 2006). Mammals, however (e.g., Huhman et al. 2003; Oyegbile & Marler 2005; Jennings et al. 2009), seem to have received less attention regarding winner and loser effects than other organisms such as fishes (e.g., Hsu et al. 2009; Oliveira et al. 2009). This is true even for rodents, including the most widespread model organisms for behavioral studies such as rats (c.f. Oyegbile & Marler 2005), even though winner and loser effects are well suited as models to study proximate hormonal and neural mechanisms of interactive behavior and social conflict (Huhman 2006; Fuxjager & Marler 2010). Adaptive explanations of winner and loser effects are based on the provisioning of information on Correspondence Stephan R. Lehner, Department of Behavioral Ecology, Institute of Ecology and Evolution, University of Bern, Ethologische Station Hasli, Wohlenstrasse 50a, 3032 Hinterkappelen, Switzerland. E-mail: [email protected]