How Inhibitory Control Relates to Positive and Negative Affective States in Red Junglefowl

Different social experiences drive the development of divergent stress coping styles in female swordtails (Xiphophorus nigrensis)

Individual variation in stress coping styles is widespread and consequential to health and fitness. Proactive (bold behavior, low stress reactivity, low cognitive flexibility) and reactive (shy behavior, high stress reactivity, high cognitive flexibility) coping styles are found in many species, but the developmental forces shaping them remain elusive. We examined how social influences, specifically mating interactions, shape the development of adult female coping styles with a manipulative rearing experiment using El Abra swordtails, Xiphophorus nigrensis. We raised juvenile females in environments with different male reproductive phenotypes: coercive-only, courting-only, or complex (both coercive and courting males). At adulthood, we measured female stress reactivity (cortisol release following acute stress), boldness (scototaxis and open field responses), and cognitive flexibility (as inhibitory control in a detour task). Females raised in coercive and complex environments developed higher cortisol reactivity than females raised with only courtship. Stress coping trait correlations varied significantly across social environments producing different coping styles across treatments. Traditional proactive and reactive stress coping styles developed in the coercive-only environment with negative correlations between stress response and boldness, stress response and cognitive flexibility, and boldness and cognitive flexibility. Meanwhile, the courtship-only environment produced a negative correlation between stress response and boldness. We thus demonstrate that the relationship between stress response and boldness can be socially modulated. These findings suggest that developmental variation in social experiences can shape suites of traits with complex relationships; and that highly stressful social interactions, such as sexual coercion, can be a strong driver of stress coping styles.

Increased dietary 5-hydroxytryptophan reduces fearfulness in red junglefowl hens (Gallus gallus)

Our production animals typically suffer poor welfare, which can be revealed by measuring the affective state these animals are in. Negative affective state is linked to poorer welfare, and can be measured as fearfulness. While continuing to research how to improve animal welfare, a compliment to reduce negative affective state could therefore be to reduce individuals' fearfulness, similar to how negative affective states are medicated in humans. A proposed mechanism for this is via the monoaminergic systems. This is based on previous studies across species that have linked the serotonergic system and fear-related behaviour. We here aimed to experimentally manipulate the serotonergic system in red junglefowl hens (Gallus gallus), the main ancestor of all domesticated chickens. We measured fearfulness as latency remaining immobile in a tonic immobility test, and did so both before and after our experimental manipulation. We set out to experimentally manipulate the serotonergic system via sub-chronic dietary treatment of 5-hydroxytryptophan (the precursor to serotonin). Our dietary manipulation of 5-hydroxytryptophan significantly reduced measured fearfulness in the manipulated hens, while latency in tonic immobility did not significantly change in our unmanipulated, control hens. This finding is promising since it indicates that increased tryptophan levels can be used to reduce fearfulness. Additionally, our result suggests that this can be done non-invasively via food (instead of injections), thus presenting a potentially feasible manipulation also for larger settings. Nevertheless, the serotonergic system is complex and its role in modulating behaviour in the fowl should be explored further to evaluate our findings, and more directly explored also in a production setting.

Horses wait for more and better rewards in a delay of gratification paradigm

Self-control, defined as the ability to forgo immediate satisfaction in favor of better pay-offs in the future, has been extensively studied, revealing enormous variation between and within species. Horses are interesting in this regard because as a grazing species they are expected to show low self-control whereas its social complexity might be linked to high self-control abilities. Additionally, self-control may be a key factor in training and/or coping with potentially stressful husbandry conditions. We assessed horses' self-control abilities in a simplified delay of gratification test that can be easily implemented in a farm setting. In Experiment 1, we gave horses (N = 52) the choice between an immediately available low-quality reward and a delayed high-quality reward that could only be obtained if the horse refrained from consuming the immediate reward. Different experimenters (N = 30) that underwent prior training in the procedures, tested horses in two test phases either with their eyes visible or invisible (sunglasses). Twenty horses waited up to the maximum delay stage of 60 s while all horses performed worse in the second test phase. In Experiment 2, we improved the test procedure (i.e., one experimenter, refined criterion for success), and tested 30 additional horses in a quality and quantity condition (one reward vs. delayed bigger reward). Two horses successfully waited for 60 s (quality: N = 1, quantity: N = 1). Horses tolerated higher delays, if they were first tested in the quantity condition. Furthermore, horses that were fed hay ad libitum, instead of in a restricted manner, reached higher delays. Coping behaviors (e.g., looking away, head movements, pawing, and increasing distance to reward) facilitated waiting success and horses were able to anticipate the upcoming delay duration as indicated by non-random distributions of giving-up times. We found no correlations between owner-assessed traits (e.g., trainability and patience) and individual performance in the test. These results suggest that horses are able to exert self-control in a delay of gratification paradigm similar to other domesticated species. Our simplified paradigm could be used to gather large scale data, e.g., to investigate the role of self-control in trainability or success in equestrian sports.