Host density and ectoparasite avoidance in the common lizard (Lacerta vivipara).

Increased transmission of parasites and diseases is generally considered as a major cost of social life. In this study we tested the hypothesis regarding ectoparasites as a cost of living in crowded habitats in the common lizard (Lacerta vivipara). We used two approaches to explore this question. First, we tested if ectoparasite load and prevalence are positively correlated with host density in the field. Second, we experimentally tested if lizards avoid parasitized conspecifics. Contrary to expectation, we found that (1) ectoparasite load is negatively correlated with lizard density; (2) prevalence does not significantly increase with density; (3) unparasitized lizards do not avoid parasitized conspecifics but are attracted by them whatever their parasite load. These findings suggest that ectoparasites cannot be considered as a cost of living at high density in the common lizard, in spite of the potential negative impact mites may have on lizard fitness.