Emotional state of collared peccary (Mammalia, Tayassuidae) during a nutritional experiment using the cognitive judgment bias paradigm (#171)
We used a judgment-bias paradigm to evaluate whether space restriction affects the emotional state of collared peccary (Pecari tajacu) during a nutritional experiment. We trained six adult peccaries to ‘go’ to receive a food reward when a positive auditory cue (whistle; CS+) was given, and to ‘no-go’ to avoid a punisher when a negative cue (percussion instrument noise; CS-) was sounded. An ‘ambiguous’ auditory cue (drumstick hitting an aluminum plate; CSA) was presented to probe decision-making under ambiguity. This resulted in no reward or punishment. Individuals were subjected to five tests: T1 (no-space restriction), T2 (space restriction without environmental enrichment), T3 (no-space restriction), T4 (space restriction with environmental enrichment), T5 (no-space restriction). Each animal was exposed to 10 judgment bias trials of each of the three cue types. We recorded whether animals showed the ‘go’ or ‘no-go’ response after each kind of cue. We also determined fecal glucocorticoid metabolite concentrations during tests. Throughout all tests, the peccaries distinguished between positive and negative auditory cues (0.5±0.2 vs. 0.2±0.3, Ps<0.05). During T1, T4, and T5 tests there were no differences in the proportions of ‘go’ responses between CSA and CS+ (0.5±0.3 vs. 0.3±0.3, Ps>0.07) and between CSA and CS- (0.5±0.3 vs. 0.3±0.3, Ps>0.70). During T2 and T3 tests, however, they showed higher proportions of ‘go’ responses (Ps<0.05) to CS+ (0.5±0.0) than to both CSA and CS- (0.3±0.0 vs. 0.2±0.1, P=0.54), which occurred in similar proportions. They thus appeared to treat the ambiguous cue similarly to the negative cue. Moreover, during T2 and T3, fecal glucocorticoid metabolite concentrations were higher than during the other tests (208.0±16.4 vs. 141.6±25.9ng.g-1 dry feces, Ps<0.03). Our results indicate that space restriction may lead to physiological stress and a ‘pessimistic’ cognitive bias in peccaries, which may be prevented by environmental enrichment.