Evolution of reduced pre-adult viability and larval growth rate in laboratory populations of Drosophila melanogaster selected for shorter developmenttime

Four large (n > 1000) populations of Drosophila melanogaster, derived from control populations maintained on a 3 week discrete generation cycle, were subjected to selection for fast development and early reproduction. Eeg. to eclosion survivorship and development time and dry weight at eclosion were monitored every 10 generations. Over 70 generations of selection, developm ent time in the selected populations decreased by approximately 36 h relati ve to controls, a 20% decline. The difference in male and female developmen t time was also reduced in the selected populations. Flies from the selecte d populations were increasingly lighter at eclosion than controls, with the reduction in dry weight at eclosion over 70 generations of selection being approximately 45 % in males and 39 % in females. Larval growth rate (dry w eight at eclosion/development time) was also reduced in the selected lines over 70 generations, relative to controls; by approximately 32 % in males a nd 34 % in females. However, part of this relative reduction was due to an increase in growth rate of the controls populations, presumably an expressi on of adaptation to conditions in our laboratory. After 50 generations of s election had elapsed, a considerable and increasing preadult viability cost to faster development became apparent, with viability in the selected popu lations being about 22 % less than that of controls at generation 70 of sel ection.