Human-affiliative red foxes (Vulpes vulpes) are also affiliative toward conspecifics: Testing the behavioral syndrome in the self-domestication hypothesis

抄録

The red fox domestication experiment selected for tame responses toward humans, establishing a behavioral syndrome (low fear, low aggression, high affiliativeness) here termed "tameness syndrome." The self-domestication hypothesis assumes such human-directed traits correlate with conspecific-directed traits, but this remains insufficiently tested. I examined behavioral syndromes in 41 captive red foxes (Vulpes vulpes) aged 0–2 years at a tourist facility in Hokkaido, Japan. Using focal animal sampling from 2021 to 2023, behaviors toward tourists and conspecifics were recorded. Principal component analyses extracted one component for human-directed behavior (PC1: affiliativeness) and three for conspecific-directed behavior (PC1: aggressiveness–tolerance, PC2: affiliativeness, PC3: fearfulness). A linear mixed-effects model revealed that human-directed affiliativeness was positively associated only with conspecific-directed affiliativeness, not with aggressiveness–tolerance or fearfulness. Human-directed aggression was absent, likely because foxes were not cornered. These results suggest that increased affiliativeness, rather than reduced aggression, is the primary trait under selection in self-domestication. Furthermore, only conspecific-directed affiliativeness was positively correlated with human-directed affiliativeness, suggesting that affiliativeness toward both humans and conspecifics may be co-selected during self-domestication, whereas reduced conspecific aggression or fear plays a minimal role.