Prevalence of Same-Sex Sexual Behavior in Termites: Persistence Under Mate-Seeking Stress Absence.

Same-sex sexual behavior is an enigma in behavioral ecology as it does not result in reproduction. Previous studies on the evolution of same-sex sexual behavior have primarily focused on factors such as recognition mechanisms, resource constraints, and challenges in securing an opposite-sex partner, while overlooking the investigation into active same-sex sexual behavior without environmental stress. Here, through experimentation, we investigated the stability of same-sex pairs in tandem running, the mating behavior of pairs that form same-sex tandem runs, and the occurrence of same-sex sexual behavior (SSB) when opposite-sex partners are available. Results indicated that while the stability of same-sex tandems is lower than that of opposite-sex tandems, both males and females are capable of expressing sex-specific behaviors typical of the opposite sex and forming same-sex tandems. Notably, SSB was observed not only in same-sex pairing contexts but also when individuals had the autonomy to choose between same-sex and opposite-sex partners. These results demonstrate that same-sex sexual behavior in termites is not a behavioral response to environmental stress (e.g., the absence of opposite-sex partners) but rather an actively expressed behavior. These findings highlight the role of sex role plasticity in the evolution of same-sex sexual behavior, providing a new mechanistic perspective for understanding same-sex sexual behavior in social insects.