To beat or not to beat: Behavioral plasticity during the antler growth period affects cortisol but not testosterone concentrations in red deer (Cervus elaphus) males

The effects of challenge or social buffering on cortisol, testosterone, and antler growth in captive red deer (Cervus elaphus) males

We equipped 17 captive red deer males (Cervus elaphus) with GPS collars to measure inter-individual distances throughout the 5-months of the antler growth period. We expected some individuals to associate regularly with others while others would not. We predicted that males aggregating with others within a socially stable environment (Associates) would benefit from a form of "social buffering" and would likely have lowered cortisol (C) and testosterone (T) concentrations. Males only irregularly joining social groupings would experience elevated levels of aggression; according to the "Challenge hypothesis", their T and C concentrations should increase. Interacting with a higher proportion of Associates did indeed reduce C concentrations. Conversely, avoiding Associates and challenging other males stimulated the T secretion. Admittedly, males avoiding regular proximity to others tended to develop the largest antlers. They probably benefited from frequent successful agonistic threats to conspecifics, resulting in elevated T concentrations. Regular association with tolerant, conspecifics and "social buffering" did not seem sufficient for producing larger antlers despite reducing C concentrations. Alternative social strategies were adopted within the same group of individuals and showed how the trade-off between these strategies could have an essential impact on C and T concentrations.

Coping styles vary with species' sociality and life history: A systematic review and meta-regression analysis

Despite a long history of animal studies investigating coping styles, the causal connections between behavior and stress physiology remain unclear. Consistency across taxa in effect sizes would support the idea of a direct causal link maintained by either functional or developmental dependencies. Alternatively, lack of consistency would suggest coping styles are evolutionarily labile. Here, we investigated correlations between personality traits and baseline and stress-induced glucocorticoid levels using a systematic review and meta-analysis. Most personality traits did not consistently vary with either baseline or stress-induced glucocorticoids. Only aggression and sociability showed a consistent negative correlation with baseline glucocorticoids. We found that life history variation affected the relationship between stress-induced glucocorticoid levels and personality traits, especially anxiety and aggression. The relationship between anxiety and baseline glucocorticoids depended on species' sociality with solitary species showing more positive effect sizes. Thus, integration between behavioral and physiological traits depends on species' sociality and life history and suggests high evolutionary lability of coping styles.

"How not to judge a deer by its cover": A personality assessment study on captive adult red deer males (Cervus elaphus)

Personality is not a uniquely human characteristic and it has been documented in a wide range of organisms, from mammals to birds, reptiles, fish, and invertebrates. However, personality is still poorly understood in Cervids. Therefore, our study aimed to fill this gap by i) investigating personality and ii) exploring its links to dominance hierarchy, assessed by behavioral observations in 11 captive and tame male red deer (Cervus elaphus). Using questionnaires to assess personality, three trained volunteers rated these animals in 15 behaviorally composed adjectives with detailed descriptions, based on their overall impression at the end of the observation period. Behavioral data from animals were collected across three different situations, namely "feeding" (i.e., high competition for a scarce resource), "normal" (i.e., no external stimuli) in a group setting, and "handling" (i.e., stressful situation due to human manipulation) in an individual setting. We estimated dominance hierarchies between the individuals based on situations of average and high competition (i.e., "normal" and "feeding") via the Clutton-Brock Index (CBI). Using Fleiss' Kappa for inter-rater reliability, only five of our 15 behavioral adjectives showed acceptable reliability. Using principal component analysis, four of these adjectives formed one personality component labelled "Confidence/Aggressiveness". We found that although "Confidence/Aggressiveness" did not correlate with CBI, ratings of two adjectives loading onto this component, namely "Confident" and "Submissive", significantly correlated with the CBI, indicating that the questionnaire ratings reflect real behavioral variation in red deer males. Our study provides the first assessment of personality in male red deer and adds to the growing literature on Cervid personality, offering the basis for future personality research in ungulates.