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Abstract
Anurans are known to feign death as a way to avoid or minimize the risk of predation. However, information on this defensive strategy is scattered and we believe that there is more than one behaviour type referred to as thanatosis. Here we review the literature, add original data, and propose definitions and new names that complement the present knowledge on the subject. We collected information on 334 individuals of 99 species in 16 families and grouped the recorded displays into two categories of tonic immobility: (1) thanatosis, death-feigning, or playing possum, and (2) shrinking or contracting. These two categories are treated as different behaviour types because of the display pattern (position of fore- and hindlimbs, eye opening), presence of skin toxins (shrinking is mostly displayed by toxic species, whereas thanatosis is mostly displayed by non-toxic species), social context (interaction with predators), and their putative or actual functions.
Acknowledgements
André Antunes, Cynthia Prado, Daniel Loebmann, Juliana Zina, Luís Giasson, Marlies Sazima, Nanuza L. Menezes, Olívia Araújo, Otávio Cardoso de Oliveira, Rodrigo Lingnau, Werner C. A. Bokermann helped in the field expeditions. Anne D'Heursel, Itamar Martins, Rogério Bastos, Ricardo Sawaya, Andreas Schmitz, Cynthia Prado, Julián Faivovich, Louise Allcock, and Wolfgang Böhme helped with references and with valuable comments during early drafts of the manuscript. Andreas Schmitz provided the pictures of Leptopelis rufus and Acanthixalus spinosus. FAPESP and CNPq supported the Herpetology laboratory, Departamento de Zoologia, Unesp, Rio Claro, São Paulo, Brazil. The authors also thank, CNPq, FAPESP (process no. 2008/50325-5), Idea Wild, Neotropical Grassland Conservancy, and Fauna Pro Assessoria e Consultoria Ambiental for grants, scholarships, equipment donation, and supporting some of the field expeditions. IS (retired) is presently associated as a voluntary researcher with the Museu de Zoologia, Universidade Estadual de Campinas.
