Size and seasonal temperature in free-ranging Drosophila subobscura

Body size of diverse ectotherms is inversely related to developmental tempe rature in the laboratory. We monitored seasonal variation in wing length of two populations (Oregon, Washington) of D. subobscura, which was introduce d in the Pacific Northwest in the late 1970s. Wing length varied seasonally and was shortest in summer. In Washington, however, wing length was longes t in spring, not winter. Wing length was inversely and curvilinearly relate d to mean ambient temperature, as in a few previous studies of drosophilids . Mid-winter D. subobscura might not be the largest either because extremel y low temperatures depress size or because flies collected in winter were i n fact born the previous autumn, when developmental temperatures were more moderate. (C) 2000 Elsevier Science Ltd. All rights reserved.