2005): Variation in preferred body temperature in an oviparous population of Lacerta (Zootoca) vivipara

The intraspecific variation of preferred tempera-tures (Tp) was analysed in an oviparous population of Lacerta vivipara and compared with viviparous popu-lations. Lizards collected in central Pyrenees were exposed to a thermal gradient and Tp was measured at four time intervals. Tp was strongly dependent on liz-ard condition (males> non-pregnant females> pregnant females = immatures) and more weakly with time of day (early morning> mid-day). Individual fe-males increased their Tp after egg-laying. Class-by-class comparisons did not reveal substantial differences with viviparous populations as expected for the thermal rigidity hypothesis. Nevertheless, on a short time scale, Tp should be interpreted as a compro-mise between different selective pressures including not only thermal environment but also reproductive condition and energy allocation. Key words: behaviour, lizard, thermoregulation The temperature selected in the absence of ther-moregulatory constraints (preferred body temperature, Tp) is a relevant trait highly correlated with optima for many physiological processes in lizards (Huey & Bennet, 1987; Bauwens et al., 1995). Two kinds of vari-ability in Tp should be considered: among populations/ species and within a population. At the population/spe-cies level, evidence for both rigidity and flexibility on an evolutionary scale has been found in many lizard groups (i.e. Hertz et al., 1983; Bennet & John-Alder, 1986; Christian & Weavers, 1996; Castilla et al., 1999). These discrepancies probably stem from different rates of response to directional selection for this trait across evolutionary lineages (Labra, 1998). Studies on lacertids seem to support the thermal rigidity hypothesis within this family (Van Damme et al., 1989a, 1990