“…DRAGOSLAV MARINKOVIC, DAVID w. CRUMPACKER, AND VICTOR M. SALCEDAt Rockefeller University, New York, New York 10021 Previous studies on genetic loads in natural populations of Drosophila have dealt with components of fitness, such as rate of development, viability, longevity, fecundity, and fertility (e.g., Dobzhansky and Spassky, 1953;Dobzhansky, Spassky, and Tidwell, 1963;Hiraizumi and Crow, 1960;Marinkovic, 1967aMarinkovic, , 1967b. The present experiment extends this approach to the consideration of a specific environmental factor, namely, cold temperature.…”