The Herpetological Journal

Authors: Igor Gerolineto-Alves, Fernanda Sousa Santos, Ramon Cavalcanti & Wilian Vaz-Silva

Abstract: Communication in anurans occurs mainly through acoustic and visual signals, both of which are essential for reproductive success and territorial defence. Despite their importance, many visual behaviours remain poorly understood, particularly those associated with signalling. In this study, we present the first record of toe-trembling behaviour in Boana caiapo, an endemic species of the Brazilian Cerrado, and provide a comprehensive review of the different types of visual communication reported in anurans. Field observations were conducted in October 2024 in a gallery forest area in the municipality of Itapirapuã, Goiás State, Brazil, using nocturnal active searches and acoustic playback stimulation. Four adult males in reproductive activity were documented, all of which displayed toe trembling, characterised by rapid, arrhythmic tremors of the digits on both fore and hind limbs, without lifting the feet from the substrate. This behaviour occurred at intervals of one to three seconds and was observed in approximately 70% of the advertisement calls, suggesting a role in multimodal communication during courtship, particularly in environments with high levels of acoustic interference. Our literature review identified 29 types of visual signalling behaviours reported worldwide in anurans, distributed across 98 species and two genera from 17 families. Hylidae exhibited the highest number of species with visual displays, most frequently involving limb lifting and toe trembling, often associated with agonistic interactions and courtship. The behaviour observed in B. caiapo differs from that reported in some congeners, in which toe trembling is primarily linked to male-male agonistic encounters. Instead, in B. caiapo, this behaviour appears to be more closely associated with advertisement calling and mate attraction. These findings highlight the importance of documenting novel signalling strategies, as they expand our understanding of the behavioural plasticity and multimodal communication strategies of anurans under diverse ecological pressures.

Keywords: multimodal communication, agonistic interactions, courtship behaviour, Cerrado biome, Hylidae