Integumentary toxicity and unpalatability as an antipredator mechanism in the narrow mouthed toad, Gastrophryne carolinensis

Abstract

Gastrophryne carolinensis was eaten by four potential vertebrate predators, significantly less frequently than control anurans. The combined responses of all predators was to reject G. carolinensis in 60% of the experimental trials (χ2 = 20.49; p < 0.01), whereas controls were rejected in less than 5% of trials (7/150). The most frequent response of all predators was to contact, bite, and then release the unharmed frog. Prolonged periods of distress by the predators following contact with the toad and the additional time needed for ingestion make it energetically disadvantageous to eat G. carolinensis when alternatives are available. Injections of 3 mg G. carolinensis skin per gram body weight killed mice within 15 min. Rana catesbeiana skin caused no observable distress behaviors.Granular and mucous glands are found in the stratum spongiosum of all regions of the skin of G. carolinensis and G. olivacea adults. Scanning electron micrographs of secretory gland pores reveal a uniform distribution of the glands throughout the body covering. In tadpoles the pores and underlying glands appear in the dermis of the skin at the time of forelimb emergence, which coincides with the onset of toxicity. Skin secretions also function in the feeding ecology of Gastrophryne spp. by protecting the frogs from counterattacks from ants, their primary prey.