Size-Dependent Chemosensory Responses to Familiar and Unfamiliar Conspecific Faecal Pellets by the Iberian Rock-Lizard, Lacerta monticola


Corresponding author: Pilar López, Departamento de Ecología Evolutiva, Museo Nacional de Ciencias Naturales, CSIC, José Gutiérrez Abascal 2, E-28006 Madrid, Spain. E-mail:


We conducted a field study to analyse the social relationships between males of the Iberian rock lizard (Lacerta monticola). The degree of familiarity was determined based on the degree of overlap between their home ranges. We then designed a laboratory experiment to test whether the same males were able to discriminate between familiar and unfamiliar conspecifics using faecal pellet odours. Differential tongue-flick rates suggest that large males (snout-to-vent length, SVL > 75 mm), at least, may discriminate between odours of familiar and unfamiliar males. The behavioural responses were dependent on relative differences in body size between the responding male and the male that donated the faecal pellet. Thus, as responding small males increased in size relative to their corresponding familiar male, their rate of tongue-flicking significantly decreased; this was not the case in response to unfamiliar males. In contrast, there were no significant correlations between the response of large males to familiar or unfamiliar male stimuli, regardless of size differences. These results suggest that chemical cues contained in faecal pellets allow individual recognition in male L. monticola, and that the response depends on body size. We suggest that faecal pellets might be used to scent-mark home ranges, which would contribute to lowering the costs of aggressive interactions.