Measuring evolutionary responses to global warming: cautionary lessons from Drosophila

Understanding evolutionary responses to global climate warming can be daunt- ingly complex. But, primarily, it requires carefulquantification of rates of temporal change of bio- monitors. 2. Long-term biomonitoring programs capitalize on traits for which there already exist retro- spective measurements. Those programs are thus faced with the decision as to the appropriate time to update historical records, especially in species whose gene frequencies cycle over the successive seasons. In these cases, the time during the year at which descendant populations are sampled needs to take into account effects of the lengthening growing season that can impose direct selec- tion on specific genotypes and, concomitantly, indirect selection on photoperiodic response. 3. Standardising new and past collections by ca lendar date can lead to an overestimation of the magnitude of long-term responses to global warming; standardising by equivalent seasonal tem- perature conditions can lead to an underestimation of the magnitude of long-term responses to glo- bal warming. 4. The results of a recent monitoring study with Drosophila indicate that caution should be exer- cised in how the updating of historical records is used to quantify evolutionary responses to global warming.