Unkenreflex in anurans– new observations with a review of published records

Abstract

Amphibians have evolved diverse anti-predator defences, including behavioural ones. One of the best known is unkenreflex. It was described for the first time in Firebellied Toads Bombina; spp. and it is, in its classic form, a display of conspicuous underside by lifting limbs and arching back upon disturbance. Unkenreflex has also been recorded in other anurans, but its prevalence across species has not been extensively studied so far. Here, we present our own observations and review published records, distinguishing full and partial unkenreflex. We document 23 cases of unkenreflex, including the first records in Pelobates fuscus, Bufotes viridis, Bufo bufo, Pelophylax esculentus complex, and Hyla arborea. Combining these findings with previously published records, in 43 species partial unkenreflex has been reported, in 34 species full unkenreflex, while both types were observed in seven species. Regarding family and biogeographic realm, the True Toads (Bufonidae) and Neotropics had the highest number of species in which unkenreflex was reported. Our review clearly shows that unkenreflex is more widespread among anurans than previously thought. Full unkenreflex likely conveys survival advantages through aposematism and deimatism, while partial reflex may rely on mechanisms such as protecting eyes, increasing body width to deter swallowing, obscuring head location, and feigning death (thanatosis). Robust large-scale sampling and experiments are needed to fully elucidate the prevalence, role, distal mechanisms, and evolution of this fascinating and understudied behaviour.