<p>Adult sex ratio (ASR, the proportion of males in the adult population) is a key demographic parameter shaping social dynamics, yet its influence on the expression of animal personality and behavioral syndromes remains poorly understood. Using controlled ASR manipulations in the dung beetle <i>Onthophagus taurus</i>, we assessed the effects of ASR on four candidate behavioral traits—righting, antipredator boldness, foraging exploration, and aggressiveness—and their intercorrelations. Behavioral repeatability and syndrome structure were quantified pre- and post-manipulation via standardized assays. We found that righting and aggressiveness exhibited high repeatability, whereas antipredator boldness and foraging exploration showed lower consistency. These four traits formed a behavioral syndrome characterized by a strong positive correlation between righting and foraging exploration, and significant positive correlations of antipredator boldness and aggressiveness with both righting and foraging exploration. No correlation was detected between antipredator boldness and aggressiveness. Contrary to expectations, ASR treatments (female-biased, unbiased, male-biased) did not alter traits expression or reshape syndrome architecture. Instead, prolonged attacking duration and righting time post-manipulation implicated social experience—rather than specific ASR context—as a key behavioral modulator. Body size emerged as a critical predictor of aggressiveness and traits correlations, highlighting intrinsic (e.g. morphological traits) over extrinsic (e.g. limited ASR) drivers of personality variation. These results challenge assumptions about ASR-mediated behavioral plasticity and underscore the need to integrate morphological and experiential factors in animal personality research.</p>