Mental gland secretions as a social cue in gopher tortoises (Gopherus polyphemus): tortoise presence stimulates and maintains social behaviour with chemical cues

Abstract

Multimodal signalling reinforces specific messages in communication. In gopher tortoises, similar to other reptilian species, visualization of conspecific and chemical exudates from the skin may serve as a multimodal display advertising information about conspecific species, sex, or individual qualities, but this has not been fully elucidated. For gopher tortoises, one such possible source of chemical cues could be secretions from seasonally enlarged mental glands (MG). Here, we used both sexes of gopher tortoises in a paired choice presentation of MG secretions vs. distilled (DI) water on resin tortoise models to assess visual presence with tortoise-specific secretions. We examined behaviours to treatments to examine if MG secretions are recognizable olfactory cues and if visual cues alone are sufficient to maintain social interactions using a simple visual presentation vs. a complex visual and olfactory presentation. Tortoises of both sexes spent more total time (p < 0.001) and performed a greater number of behaviours (p < 0.001) towards the MG-treated model, relative to the neutral control (DI-treated model), suggesting that olfactory MG secretions are also required, along with visual presence of a tortoise, to engage in social behaviours. Our results are among the first for this species suggesting that pheromone usage may drive social interactions in social behaviours.