Mainland versus island differences in behaviour of Podarcis lizards confronted with dangerous prey: the scorpion Buthus occitanus A.M. Castilla a,b* , A. Herrel c,d and A. Gosa ´ e a Estacio ´n Biolo ´gica de Sanau ¨ja, Museo Nacional de Ciencias Naturales (CSIC), Ministerio de Ciencia e Innovacio ´n, E-Lleida, Spain; b Department of Biodiversity and Evolutionary Biology, Museo Nacional de Ciencias Naturales de Madrid (CSIC), Madrid, Spain; c Organismic and Evolutionary Biology, Harvard University, Cambridge, MA, USA; d Department of Biology, University of Antwerp, Belgium; e Departamento de Vertebrados, Sociedad de Ciencias de Aranzadi, San Sebastia ´n, Spain (Received 1 February 2008; final version received 5 June 2008) Rapid divergence in behaviour of populations invading novel habitats is often considered adaptive as it may allow a species to exploit novel resources. Here we explore the behavioural response of two closely related species of Podarcis lizards living in different habitats, the Spanish mainland and a dry volcanic island, towards a potentially dangerous prey. Our results show that whereas insular lizards attacked scorpions and consequently considered them to be potential prey, mainland lizards tended to flee or ignored them. Sexual differences in the response to scorpions were pronounced in the insular habitat. Males tended to attack scorpions while females tended to ignore them. Inter-specific and inter-sexual differences in the responses of lizards may be mediated by body size differences between populations and sexes. The rapid changes in behaviour allowing insular lizards to recognize scorpions as potential prey may have allowed these animals to capitalize on an abundant food resource in a depauperate environment. Keywords: poison; feeding; Mediterranean; Columbretes; sexual differences; evolution Introduction In habitats with low productivity, insectivorous lizards often consume a high proportion of plants (Colli et al. 1998; Herrel et al. 2004), marine invertebrates (Grismer 1994; Catenazzi and Donnelly 2007), seabird regurgitates, or even resort to scavenging (Castilla et al. 1987). Although most lizards avoid potentially dangerous prey like scorpions, there are some scorpion predators or specialists (McCormick and Polis 1990; O’Connell and Formanowicz 1998, Zlotkin et al. 2003). In arid habitats scorpions can be extremely abundant (Polis 1990) compared with other potential prey, suggesting that behavioural or morphological adaptations that would allow lizards to consume these prey may be selected for in environments with low food abundance. The endemic lizard Podarcis atrata inhabits small islands of the volcanic Columbretes archipelago (Mediterranean, Spain). The islands are characterized by an extreme aridity and by the scarcity of terrestrial insects (Castilla and Bauwens 1991a). Adult lizards consume isopod crustaceans (Castilla et al. forthcoming 2008) *Corresponding author. Email: aurora@mncn.csic.es Journal of Natural History Vol. 42, Nos. 35–36, September 2008, 2331–2342 ISSN 0022-2933 print/ISSN 1464-5262 online # 2008 Taylor & Francis DOI: 10.1080/00222930802254763 http://www.informaworld.com Downloaded By: [Thomas, Rebecca][informa internal users] At: 09:38 10 September 2008