Supplementary material from "Coordination of movement via complementary interactions of leaders and followers in termite mating pairs"

In collective animal motion, coordination is often achieved by feedback between leaders and followers. For stable coordination, a leader's signals and a follower's responses are hypothesized to be attuned to each other. However, their roles are difficult to disentangle in species with highly coordinated movements, hiding potential diversity of behavioural mechanisms for collective behaviour. Here, we show that two <i>Coptotermes</i> termite species achieve a similar level of coordination via distinct sets of complementary leader-follower interactions. Even though <i>C. gestroi</i> females produce less pheromone than <i>C. formosanus</i>, tandem runs of both species were stable. Heterospecific pairs with <i>C. gestroi</i> males were also stable, but not those with <i>C. formosanus</i> males. We attributed this to the males' adaptation to the conspecific females; <i>C. gestroi</i> males have a unique capacity to follow females with small amounts of pheromone, while <i>C. formosanus</i> males reject <i>C. gestroi</i> females as unsuitable but are competitive over females with large amounts of pheromone. An information-theoretic analysis supported this conclusion by detecting information flow from female to male only in stable tandems. Our study highlights cryptic interspecific variation in movement coordination, a source of novelty for the evolution of social interactions.