Neotropical dancing frog: the rich repertoire of visual displays in a hylodine species

During reproductive season, males usually must defend their territory against competitor males and attract females for reproduction. Acoustic signals evolved as an alternative to physical attacks, thus reducing injuries to both opponents during a territorial dispute, but they are also the primarily trait used by female frogs to select males. However, there is some recent evidence that visual signalling also can be important during social interactions in frogs. Here, for the first time, we describe the sophisticated visual behaviour of Hylodes meridionalis, a diurnal species that is endemic to the southern Atlantic Forest, where it inhabits fast streams. We submitted resident males to mirror self-image presentations to simulate the presence of an intruder male in their territories. Furthermore, we collected observations from close-range interactions between individuals of this very shy species. We observed seven types of visual displays: toe flagging (slow up-and-down movements of one or more toes), arm lifting (rapid up-and-down movements of one arm), leg lifting (rapid up-and-down movements of one leg), arm waving (lifting an arm and waving it in an arc), both legs kicking (rapidly stretching both hind limbs towards the back), foot flagging (slowly raising one hind limb in a semi-arch movement) and throat display (pulsation of one or both paired lateral vocal sacs without sound production). Only the kicking of both legs was displayed exclusively by females; toe flagging and foot flagging were displayed by males only during agonistic interactions. The frequency of visual displays (7 types, 117 events) was much greater than that of acoustic signals (3 types, 66 events). Our data demonstrate that the visual repertoire of the genus Hylodes is richer than previously noted and that visual display behaviour in anurans could be more common than previously believed. Therefore, this characterisation study aids our understanding of the function of the rich repertoire of visual displays in frog species and highlights that ethologists should be directing more of their attention towards this poorly explored anuran behaviour.