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RESEARCH PRODUCT

Beyond ‘nasty neighbours’ and ‘dear enemies’? Individual recognition by scent marks in a lizard (Podarcis hispanica)

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True individual recognition (TIR), the ability to recognize conspecific individuals on the basis of identity cues, is required for the evolution of several social traits (e.g. the maintenance of dominance hierarchies). However, knowledge about the distribution and functional significance of TIR is scant in some vertebrate groups, such as reptiles. In this study we used a functional modification of a habituation-dishabituation paradigm to investigate the existence and adaptive significance of TIR in a territorial lizard (Podarcis hispanica, Lacertidae). Males discriminated between individual rivals of similar characteristics (e.g. size, weight, familiarity) solely on the basis of their scent marks. Males also remembered the spatial location of scent marks and subsequently behaved more aggressively towards rival males that consistently marked in the core than on the periphery of their experimental terrarium. Together, these results suggest that, in this species, scent marks function to identify the potential threat posed by each individual neighbour, allowing resident males to allocate their aggressive behaviour accordingly. Our findings challenge the simplistic and commonly held view that 'dear enemy' phenomena in lizards are exclusively based on familiarity asymmetries, and support an alternative threat level hypothesis in which TIR may be more important than previously acknowledged. © 2008 The Association for the Study of Animal Behaviour.