The strength of sexual signals predicts same-sex pairing in two Coptotermes termites

Abstract Same-sex sexual behavior (SSB) is an enigma in behavioral ecology as it does not result in reproduction. Proximately, the effect of sexual signals on SSB could be distinct between signal receivers and senders. For receivers, the absence of sexual signals leads to smaller phenotypic sex differences, leading to frequent accidental SSB between receivers. Alternatively, for senders, sexual signals could help locate another sender, enhancing intentional SSB. Here, we demonstrate this link between sex pheromone signaling and the frequency of same-sex pairing in two Coptotermes termites that use the same chemical as sex pheromones but in different quantities. In termites, mating pairs engage in tandem runs, where a female emits sex pheromones to guide a male as they move together in searching a potential nest site. So, females are signal senders, and males are signal receivers for sexual communication. We found that female-female tandems were more stable in C. formosanus, whose females produce more pheromones. On the other hand, although both species did not show stable male–male tandems, males of C. gestroi, whose females produce fewer pheromones, spent more time attempting to follow another male. Thus, stronger pheromones lead to sender–sender SSB, while weaker pheromones lead to receiver–receiver SSB. The proximate mechanism of SSB is diverse according to the properties of sexual communications in heterosexual contexts.