Temperature, photoperiod and life history traits in Drosophila subobscura

Temperature and photoperiod are generally reliable indicators of seasonality that have shaped the life histories of many temperate zone organisms. Anthropogenic climate change, however, may alter historical weather patterns and seasonal cues. Many studies have evaluated thermal effects on life history traits, but fewer have also examined photoperiodic effects. Because the degree of seasonal cue varies across latitude, we examine developmental plasticity in Drosophila subobscura populations sampled from latitudinal clines across Europe and North America. We examine the interaction between temperature and photoperiod on insect development time, adult survival, and fitness using a two by two factorial design with long (16L:8D) and short days (8L:16D) at high (23{degrees}C) and low temperatures (15{degrees}C).. We find that development time is dependent on both temperature and photoperiod but the low temperature/long day treatment revealed a dramatic and unexpected 4.5 day delay in eclosion. Fitness, estimated by the intrinsic rate of increase (r), showed a significant increase in response to temperature and a decrease in response to day length, and an interaction such that long-days reduced the effects of temperature. Additionally, cooler temperatures increased lifespan, and long-days reduced survivorship; temperature and day length interacted such that lifespan is relatively shorter in seasonally mismatched (long-cool, short-warm) conditions compared to matched conditions. These data highlight the importance of multiple abiotic factors in predicting species responses to climate change.