Koziel, G., A. S’khifa, S. Kirchhof, A. MacLeod, U. Joger, B. Sinervo, M. A. Carretero, T. Slimani & M. Vences

In Issues 2021

Inference of lizard preferred temperatures differs substantially among experimental methods. pp. 263-273 plus Supplementary document.

Abstract. Experimentally assessing the preferred body temperature (Tpref) of ectothermic animals is important to understand thermal adaptation. In lizards, this variable is usually estimated by measuring body temperature in thermal gradients. To quantify the extent to which different experimental setups influence the inferred Tpref values we submitted 65 individual lizards of three species to randomized tests using six different experimental setups at Oukaimeden, Morocco, including setup variants similar to those that have been most often used in lacertids. Among-treatment differences were substantial. Using an infrared bulb as heat source in combination with artificial cold lighting yielded about 5°C lower Tpref estimates than photothermal treatments with an incandescent bulb as heat and light source, possibly because lizards thermoregulated
differently without a visual cue related to the heat source, or due to the absence of a natural photoperiod. Photothermal assays in which Tpref was assessed by hourly cloacal measurements over a 10h period yielded 2.2°C lower Tpref estimates than 2h treatments where body temperature was measured every minute with a thermocouple attached to the belly. This probably reflects that the 2h treatments targeted lizards in the initial warming-up phase, whereas the 10h treatment attempts to capture the preferred temperature of a lizard over its entire daily cycle including phases of inactivity. Lastly, we observed large differences among treatments with contact thermometers versus infrared laser thermometer measurements, calling for caution when the latter are used with artificial heat sources. Our data do not provide thorough tests of the physical, behavioural or physiological causes underlying the observed differences between treatments, but illustrate that for meta-analyses where detailed comparisons are needed, a rigorous consideration of the optimal experimental setup and its consistent use will remain necessary.

Key words. Squamata, Lacertidae, Podarcis, Atlantolacerta, Scelarcis, Morocco, thermoregulation, preferred temperature, field body temperature.

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