Influence of heat transmission mode on heating rates and on the selection of patches for heating in a Mediterranean lizard

Heliothermy (heat gain by radiation) has been given a prominent role in basking lizards. However, thigmothermy (heat gain by conduction) could be relevant for heating in small lizards. To ascertain the importance of the different heat transmission modes to the thermoregulatory processes, we conducted an experimental study where we analyzed the role of heat transmission modes on heating rates and on the selection of sites for heating in the Mediterranean lizard Acanthodactylus erythrurus ( Lacertidae). The study was conducted under laboratory conditions, where two situations of different operative temperatures (38degrees and 50 degreesC) were simulated in a terrarium. In a first experiment, individuals were allowed to heat up during 2 min at both temperatures and under both heat transmission modes. In a second experiment, individuals were allowed to select between patches differing in the main transmission mode, at both temperatures, to heat up. Experiences were conducted with live, nontethered lizards with a starting body temperature of 27 degreesC. Temperature had a significant effect on the heating rate, with heat gain per unit of time being faster at the higher operative temperature (50 degreesC). The effect of the mode of heat transmission on the heating rate was also significant: at 50 degreesC, heating rate was greater when the main heat transmission mode was conduction from the substrate ( thigmothermy) than when heating was mainly due to heat gain by radiation (heliothermy); at 38 degreesC, heating rates did not significantly differ between transmission modes. At 38 degreesC, selection of the site for heating was not significantly different from that expected by chance. However, at 50 degreesC, the heating site offering the slowest heating rate heliothermic patch) was selected. These results show that heating rates vary not only with environmental temperature but also with different predominant heat transmission modes. Lizards are able to identify and exploit this heterogeneity, selecting the source of heat gain (radiation) that minimizes the risk of overheating when temperature is high.