Is temperature preference in the laboratory ecologically relevant for the field? The case of Drosophila nigrosparsa

Ectotherms are sensitive to temperature change, and predictions about a species' vulnerability to thermal change require an understanding of its thermal responses. The preferred temperature in laboratory assays is a widely used measure commonly taken as an indicator of the temperature at which ectotherms' physiological functions are optimised. The ecological relevance of laboratory-measured temperature preference has been evaluated for vertebrate ectotherms but to our knowledge not for Drosophila. Here, we assessed the links between laboratory thermal preference and habitat temperature in the alpine fly Drosophila nigrosparsa. We found that (i) in the laboratory, D. nigrosparsa preferred a temperature of about 10 °C. In the field, (ii) macrohabitat temperatures ranged from 17 to 22 °C, and (iii) microhabitat temperatures exceeded those of the macrohabitat with up to 35 °C at full sun exposure. (iv) Isotope-tracked flies were localised, among others, at nearly the maximum temperature conditions measured in the microhabitats. (v) Operative environmental temperature models revealed that air temperature has the highest impact on the flies’ experienced temperature, followed by global solar radiation and wind. These findings highlight that the preferred temperature in the laboratory differed strongly from that in the field and that different approaches lead to different conclusions about the preferred and experienced temperatures. Keywords: Field-lab dichotomy, Microhabitat, Operative environmental temperature, Preferred temperature, Thermal preference, Thermobiology