Winner and loser effects are modulated by hormonal states

Abstract

IntroductionMany animals use information acquired from recent experiences to modify their responses to new situations. Animals’ decisions in contests also depend on their previous experience: after recent victories individuals tend to behave more aggressively and after defeats more submissively. Although these winner and/or loser effects have been reported for animals of different taxa, they have only recently been shown to be flexible traits, which can be influenced by extrinsic factors. In a mangrove killifish (Kryptolebias marmoratus), for instance, individuals which lost an earlier contest were more likely than others to alter contest decisions after a recent win/loss. This result suggests that individuals perceiving themselves to have worse fighting abilities are more inclined to adjust contest strategy based on new information. If this is the case, an individual’s propensity to modify behaviour after a win/loss might also be modulated by intrinsic mechanisms related to its ability to fight. Stress and sex steroid hormones are often associated with an individual’s contest behaviour and performance, so, in this study, we tested the hypothesis that an individual’s propensity to change behaviour after wins or losses also depends on its hormonal state.ResultsOur results show that an individual’s propensity to adjust contest decisions after wins and losses does depend on its hormonal state: individuals with lower levels of cortisol (F), testosterone (T) and 11-ketotestosterone (KT) are more receptive than others to the influence of recent contest experiences, especially losing experiences, and the influences last longer. Furthermore, although winning and losing experiences resulted in significant changes in behaviour, they did not bring about a significant change in the levels of F, T, KT or oestradiol (E2).ConclusionsThis study shows that an individual’s receptivity to the influence of recent wins and losses is modulated by its internal state, as well as by extrinsic factors. Individuals with hormonal profiles corresponding to lower aggressiveness and a reduced likelihood of winning were more likely to alter contest decisions after a recent win/loss. The results also suggest that F, T, KT and E2 are not the primary physiological mechanisms mediating winner-loser effects in this fish.

Motivation but not body size influences territorial contest dynamics in a wild cichlid fish

“…differences in subjective resource value; Johnsson & Forser, 2002;Krebs, 1982). Residents may also be more likely to win contests for physiological reasons, because there are self-reinforcing effects of prior winning experience (Earley et al, 2013;Goubault & Decuigni ere, 2012;Hsu, Earley, & Wolf, 2006;Mesterton-Gibbons, 1999;Rutte, Taborsky, & Brinkhof, 2006), or because residents have a physiological advantage granted by spending the time preceding the contest in a favourable territory (Kemp & Wiklund, 2001;Kemp & Wiklund, 2004). Residents may also have a physical advantage in the contest imbued by superior positioning (Fayed et al, 2008).…”

Phenotypic differences between the sexes in the sexually plastic mangrove rivulus fish (Kryptolebias marmoratus)

“…Steroid hormone collection was conducted using a non-invasive, water-borne hormone collection technique, which has been validated for mangrove rivulus (Earley et al, 2013). This method is preferred over caudal venipuncture and whole-body assays, which would be terminal for species of this size (mass ranges from 0.25 to 1 g).…”

Fighting experience alters brain androgen receptor expression dependent on testosterone status

“…As T levels do not vary between individuals that have received different contest experiences [25], it appears that winner-loser effects operate by changing neural sensitivity to T rather than its titres. This study also showed that individuals with higher expression of ER a/b , 5-HT 1A R and GR genes were more aggressive towards larger opponents, despite the fact that expression levels of these receptors did not vary between individuals receiving different contest experiences.…”

“…Hormone levels (ln-transformed), SL and lineage were included in the model as control factors. We included interactions between experience treatments and these two hormones in the models because the fish's response to winning and losing experiences is influenced by its levels of T and F [25].…”

“…Furthermore, the fish's propensity to adjust contest decisions after wins and losses depends on its hormonal state: individuals with lower levels of F, T and KT are more likely than others to change contest behaviour after winning/losing experiences [25]. Winning/losing experiences, however, change the fish's behaviour without affecting the levels of these hormones [25], indicating that these hormones do not, alone, precipitate winner or loser effects. We therefore hypothesized that fighting experience might drive changes in the fish's behaviour by triggering changes in brain steroid and serotonin receptor gene expression.…”