Behavioural discrimination of male mental gland secretions of the gopher tortoise (Gopherus polyphemus) by both sexes

Chemical communication is important for mate choice, especially at long distances in fragmented populations. The gopher tortoise is a social species that is threatened in the southeast U.S. due to habitat fragmentation and decline. One consequence of habitat loss is reduced mating opportunities, yet chemical signalling in gopher tortoises is relatively under-studied. Here, we investigated chemoreception of tortoise discrimination of chin secretions, or mental gland (MG) secretions. To assess conspecific recognition of male MG secretions, we conducted two paired-choice experiments: one with a neutral odorant control (NC; distilled water) and one with a pungent odorant control (PC; acetone) vs. male MG secretions. Behaviours were defined a priori, and their durations were quantified relative to treatments. Each sex spent significantly more time with MG secretions vs. acetone control during the PC study (p= 0.001). Each sex also sniffed MG swabs more frequently in both studies (PC study: p=0.0003; NC study: p=0.001). A principal components analysis of behavioural durations from the PC study identified one component with a significant treatment effect performed to MG secretions (p=0.0003), including the behaviours sniffing, head bobbing, biting, and eating near a swab. Our study provides the first chemical-behavioural bioassay of MG secretions from male gopher tortoises, suggesting MG secretions may be a source of pheromones.