This dataset contains some of the data from: MacLellan, K., L. Kwan, M.C. Whitlock, and H.D. Rundle. 2011. Dietary stress does not strengthen selection against single deleterious mutations in Drosophila melanogaster. Heredity: in press. Data collectors: Kelsie MacLellan Lucia Kwan Howard Rundle, contact for questions: e-mail: hrundle@uottawa.ca All the data for this publication are contained within three files, each saved as CSV file (i.e. values separated by commas). There are no missing values. This is the first of the three. This file (rundle1_data.csv) contains the data from the environmental stress assay conducted to confirm that the novel corn-flour food increased stress relative to the standard diet. A paired design was employed in which 120 eggs were collected from a single group of stock females and then split in half and immediately transferred to two vials (i.e. 60/eggs vial), one containing the standard cornmeal food and the other containing the novel corn-flour food. Each row in the data file corresponds to one pair. The dataset has following columns: 1) block. Indicates the day (1, 2, or 3) that each replicate pair was set up. 2) rep. Replicate number (arbitrarily assigned). 3) total_ancestral. The total number of adult offspring that emerged from the standard (i.e. cornmeal-based) food vial. 4) total_novel. The total number of adult offspring that emerged from the novel (i.e. corn-flour based) food vial. 5) diff_total. The difference in the number of adult offspring emerging (total_ancestral - total_novel). 6) avg_time_ances. The # of flies emerging each day was counted until all offspring had emerged from a given vial (day zero was when the eggs were laid). This number is the average of that value over all individuals for the standard (i.e. cornmeal-based) food vial. 7) avg_time_novel. The # of flies emerging each day was counted until all offspring had emerged from a given vial (day zero was when the eggs were laid). This number is the average of that value over all individuals for the novel (i.e. corn-flour based) food vial. 8) diff_time. The difference in the average time (avg_time_ances - avg_time_novel).