Playing dead to stay alive: death-feigning in Liolaemus occipitalis (Squamata: Liolaemidae)

Biota Neotrop., vol. 10, no. 4 Playing dead to stay alive: death-feigning in Liolaemus occipitalis (Squamata: Liolaemidae) Maurício Beux dos Santos1,3, Mauro Cesar Lamim Martins de Oliveira1, Laura Verrastro2 & Alexandro Marques Tozetti1 1 Laboratório de Ecologia de Vertebrados Terrestres, Instituto de Ciências Biológicas, Universidade Federal do Rio Grande – FURG, Av. Itália, Km 8, CEP 96201-900, Rio Grande, RS, Brazil 2 Laboratório de Herpetologia, Departamento de Zoologia, IB, Universidade Federal do Rio Grande do Sul, Av. Bento Gonçalves, 9500, CEP 91501-970, Porto Alegre, RS, Brazil 3 Corresponding author: Maurício Beux dos Santos, e-mail: SANTOS, M.B., OLIVEIRA, M.C.L.M., VERRASTRO, L. & TOZETTI, A.M. Playing dead to stay alive: deathfeigning in Liolaemus occipitalis (Squamata: Liolaemidae). Biota Neotrop. 10(4): http://www.biotaneotropica. org.br/v10n4/en/abstract?short-communication+bn03110042010. Abstract: Predation is the major selective force that drives the development of a series of defense mechanisms by the species. These mechanisms are efficient in that it limits the ability of predators to detect, recognize and subdue their prey. In lizards for example, the tail loss and locomotor escape are the most common defensive behavior reported on the literature. Additionally, in response to external stimuli, some lizards exhibit a peculiar defensive behavior: death-feigning or thanatosis. Here we describe the first record of death-feigning in a population of Liolaemus occipitalis in a coastal sand dune habitat in Southernmost Brazil. A total of 86 individuals were tested. During handling 75.6% of lizards feigned death. The duration of this behavior was longer when the observer remained closer to the lizards, suggesting the ability of L. occipitalis to evaluate the predation risk. Keywords: thanatosis, behavior, sand-dune lizard, pampa, restinga. SANTOS, M.B., OLIVEIRA, M.C.L.M., VERRASTRO, L. & TOZETTI, A.M. Simulando a morte para manter-se vivo: tanatose em Liolaemus occipitalis (Squamata: Liolaemidae). Biota Neotrop. 10(4): http:// www.biotaneotropica.org.br/v10n4/pt/abstract?short-communication+bn03110042010. Resumo: A pressão exercida pela predação é a principal força seletiva que direciona o estabelecimento de uma série de mecanismos de defesa por parte das espécies. Esses mecanismos são eficientes na medida em que limitam a capacidade dos predadores em detectar, reconhecer ou subjugar suas presas. Em lagartos, por exemplo, os comportamentos defensivos mais frequentemente citados na literatura são a autotomia caudal e a fuga. Além disso, em resposta a estímulos externos, alguns lagartos podem exibir um comportamento peculiar: fingem-se de mortos (tanatose). Neste estudo descrevemos o primeiro registro de tanatose em uma população de Liolaemus occipitalis em área de dunas costeiras no extremo Sul do Brasil. Um total de 86 indivíduos foram testados. Durante o manuseio, 75,6% dos lagartos exibiram o comportamento de tanatose. A duração deste comportamento foi maior quando o observador permanecia a distâncias mais curtas dos lagartos, sugerindo uma capacidade de L. occipitalis em avaliar o risco de predação. Palavras-chave: tanatose, comportamento, lagartixa-das-dunas, pampa, restinga. http://www.biotaneotropica.org.br/v10n4/en/abstract?short-communication+bn03110042010 http://www.biotaneotropica.org.br Biota Neotrop., vol. 10, no. 4 362 Santos, M.B. et al. Introduction In general, animals show a series of traits and defensive mechanisms to avoid predation and stay alive. Organisms reduce the probability of being predated by using many adaptations or behavioral strategies, which may present specific behaviors (displays) that can discourage a predator’s attack (Greene 1988). Predation pressure is a fundamental selective force for the development of a series of traits that increase prey survival, by limiting the predator ability to detect, recognize, approach, subjugate or consume the prey (Endler 1986, Greene 1988, Lima & Dill 1990). In general, antipredator mechanisms are an important factor in the evolutionary processes of many animals (e.g., Vermeij 1982, Lima & Dill 1990). Vertebrates, in particular the Squamata, exhibit extremely diverse antipredator tactics (e.g., Pough et al. 2004, Rocha 1993), making this group an interesting model to examine evolutionary mechanisms to avoid predation (e.g., Greene 1988). In snakes, many defensive displays have been characterized including various ways of intimidating or avoiding aggressors (Greene 1988, Tozetti et al. 2009). Unfortunately, much less information is available on the defensive behavior of lizards compared to snakes. The most reported defensive behavior of lizards in the literature is tail loss (autotomy) and locomotor escape (Greene 1988, Roberts et al. 1998, Rocha-Barbosa et al. 2008). Additionally, some lizards exhibit a peculiar defensive behavior: death-feigning. Death-feigning (thanatosis) is a state of immobility assumed by many animals in response to external stimuli. This behavior has been considered a defense mechanism against predators and is shared by mammals (e.g., Francq 1969), birds (e.g., Sargeant & Eberhardt 1975), fishes (e.g., Howe 1991), amphibians (e.g., Gargaglioni et al. 2001, Bertoluci et al. 2007), reptiles (e.g., Greene 1988), and insects (e.g., Acheampong & Mitchell 1997). Death feigning is also known as catalepsy, or tonic immobility. In most cases, animals that exhibit this behavior “play dead” by maintaining a rigid posture or by simulating fully relaxed muscles (e.g. fainting; Greene 1988). Apparently thanatosis is a behavior that rarely occurs spontaneously (Greene 1988). Immobility might discourage sequential attacks, allowing escape, as demonstrated in experiments using invertebrates (Miyatake et al. 2004). While efficiency in this defensive behavior have been poorly tested, its occurrence in several vertebrate groups suggests a favorable evolutionary pressure toward its maintenance (Miyatake et al. 2004). In frogs, for example, the thanatosis was pointed out as an important secondary defense mechanism in Phillomedusa (Sazima 1974). In lizards, death-feigning has been reported for several different families, such as Anelytropsidae (Torres-Cervantes et al. 2004), Crotaphytidae (Gluesing 1983), and Scincidae (Langkilde et al. 2003). Among tropidurid lizards, this behavior has been observed in Eurolophosaurus nanuzae Rodrigues, 1981 (Galdino & Pereira 2002), E. divaricatus Rodrigues, 1984 (Gomes et al. 2004, Kohlsdorf et al. 2004) previously Tropidurus nanuzae and T. divaricatus (Frost et al. 2001), T. torquatus Wied, 1820 and T. hispidus Spix, 1825 (Bertoluci et al. 2006). Bertoluci et al. (2006) has also reported anecdotal records for several other species in the tropidurid family. Among Liolaemidae, this behavior has been reported only in Liolaemus lutzae Mertens, 1938 (Rocha 1993). This family consists of 229 species (including subspecies) belonging to the genera (...truncated)