Co-occurrence between the presence of epidermal giant cells and alarm chemical cues in tadpole skin homogenates: An ontogenetic and cross-species comparison analysis

In amphibians, intra- or interspecific chemical cues are an important source of information about possible predation risk. In anuran tadpoles, this information causes changes at different levels including behavior, morphology, and growth and development. It has been shown that chemical alarm cues trigger antipredator behaviors, such as decreased exploratory activity, in a wide variety of anuran species; however, the cellular origin of the chemical cues has not yet been confirmed by new evidence. Previous works have suggested that the alarm cues originate from a particular cell type in the skin in tadpoles of the family Bufonidae: the epidermal giant cells (GCs). Here, we confirm the presence of GCs in the epidermis of Rhinella arenarum larvae from developmental stages as early as G22, when free-swimming larvae show gregarious behavior. In addition, larval skin homogenates trigger antipredator behaviors in conspecifics from stage G22 onwards, but not at early stages (G19 and G21). This fact exposes experimental evidence for the coexistence between the appearance of GCs and the production of chemical alarm cues during the development of R. arenarum. Furthermore, the antipredator behavioral response of R. arenarum larvae triggered by skin preparations of other species that belong to the same family who also exhibit GCs allows us to speculate that chemical cues appear to be conserved among phylogenetically related species, allowing them to cross-respond to heterospecific cues. Our experimental approaches support the role of GCs as the source of alarm cues in anuran larvae of the family Bufonidae.