Combined effects of temperature and macronutrient balance on life-history traits in Drosophila melanogaster: implications for life-history trade-offs and fundamental niche

Temperature and nutrition are amongst the most influential environmental determinants of Darwinian fitness in ectotherms. Since the ongoing climate warming is known to alter nutritional environments encountered by ectotherms, a precise understanding of the integrated effects of these two factors on ectotherm performance is essential for improving the accuracy of predictions regarding how ectotherms will respond to climate warming. Here we employed response surface methodology to examine how multiple life-history traits were expressed across a grid of environmental conditions representing full combinations of six ambient temperatures (13, 18, 23, 28, 31, 33 degrees C) and eight dietary protein:carbohydrate ratios (P:C = 1:16, 1:8, 1:4, 1:2, 1:1, 2:1, 4:1, 8:1) in Drosophila melanogaster. Different life-history traits were maximized in different regions in the two-dimensional temperature-nutrient space. The optimal temperature and P:C ratio identified for adult lifespan (13 degrees C and 1:16) were lower than those for early-life female fecundity (28 degrees C and 4:1). Similar divergence in thermal and nutritional optima was found between body mass at adult emergence (18 degrees C and P:C 1:1) and the rate of pre-adult development (28 degrees C and P:C 4:1). Pre-adult survival was maximized over a broad range of temperature (18-28 degrees C) and P:C ratio (1:8-8:1). These results indicate that the occurrence of life-history trade-offs is regulated by both temperature and dietary P:C ratio. The estimated measure of fitness was maximized at 23 degrees C and P:C 2:1. Based on the shape of the response surface constructed for this estimated fitness, we characterized the fundamental thermal and nutritional niche for D. melanogaster with unprecedented detail.