Chill-coma temperature in Drosophila: Effects of developmental temperature, latitude, and phylogeny

We modify and apply a nonlethal technique for rapidly quantifying the cold tolerance of large numbers of Drosophila and other small insects. Flies are transferred to individual vials, cooled in groups in progressive 0.5 degre esC steps, and checked for loss of righting response (chill-coma temperatur e [T-cc]). Flies recover quickly when transferred to ambient temperature, a nd thus this technique potentially can be used in selection experiments. We applied this technique in several experiments. First, we examined the sens itivity of T-cc to developmental temperature. Drosophila melanogaster (Cong o, France), Drosophila subobscura (Spain, Denmark), and Drosophila ananassa e (India) were reared from egg to adult at 15 degrees, 18 degrees, 25 degre es, or 29 degreesC, transferred to 15 degreesC for several days, and then p rogressively chilled: T-cc was positively related to developmental temperat ure, inversely related to latitude of the population, but independent of se x. The sensitivity of T-cc to developmental temperature (acclimation flexib ility) was marked: T-cc shifted on average 1 degrees for each 4 degreesC sh ift in developmental temperature. Among 15 species of the obscura group of Drosophila, T-cc varied from -0.1 degrees to 4.5 degreesC; T-cc was inverse ly related to latitude in both nonphylogenetic and phylogenetically based A NCOVA (standardized independent contrasts) and was unrelated to body size.