Thermal sensitivity of two measures of fitness, Lifetime Reproductive Success (LRS, solid lines) and intrinsic rate of increase ( r , dashed lines), and the relative distribution of preferred temperatures (grey histograms). r increases with temperature to about 23°C before rapidly declining. LRS is relatively high over a relatively broad range of temperatures. Fitness values are least square means ± SEM, and mean LRS and r at each temperature are calculated from an average of 15 individuals per strain at each temperature, 402 total individuals. Each thermal preference distribution is based on the responses of an average of 1090 individuals. Arrows indicate mean thermal preferences.