Behavioral Convergence with Physiological Divergence: Sex Differences in Hormones but Not Social Behavior in Beagle...

The "experimenter gender effect" is a pervasive confound in rodent behavioral neuroscience: the sex of the human handler alters stress, social, and pharmacological responses via olfactory cues and conserved neural circuits. Whether this effect extends to dog-a species co-domesticated with humans for over 15,000 years-has never been systematically tested. Here, we examined sex-biased social preferences in Beagle dogs during both intra- and cross-species interactions, and asked whether baseline neuroendocrine states predict such preferences. Thirty-four adult Beagles (17 males, 17 females) from a standardized laboratory colony underwent social interaction tests with same and opposite-sex conspecifics and with male and female experimenters. Baseline plasma corticosterone, serotonin (5-HT), and dopamine were measured by ELISA. Results indicated that Beagles did not exhibit significant sex-based preferences for either gender of conspecifics or human experimenters in either dog-dog or human-dog social interaction tests (all p > 0.05). However, males showed markedly higher baseline corticosterone, 5-HT, and dopamine than females (all p < 0.0001), a hormonal dimorphism that did not correlate with any behavioral measure in Spearman correlation analysis (p > 0.05). Nevertheless, this study has several limitations: only baseline hormone levels were measured (not stress-induced responses), behavioral tests involved only low-stakes affiliative interactions, and only one breed was studied under standardized conditions. These results suggest that Beagle dogs may lack experimenter-gender preference in social interactions, exhibiting stable, gender-neutral social behavior despite profound underlying hormonal differences. This decoupling of internal state from behavioral output suggests that domestication may have shaped a social phenotype resistant to the experimenter gender effect, supporting the Beagle as a valuable translational model with a stable baseline and low susceptibility to confounding social cues, making it suitable for research on affective and social-cognitive disorders.