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. Egg to eclosion survivorship and development time and dry weight at
eclosion were monitored every 10 generations. Over 70 generations of selection, development time
in the selected populations decreased by approximately 36 h relative to controls, a 20% decline.
The difference in male and female development time was also reduced in the selected populations.
Flies from the selected 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 weight at eclosion/development time) was also
reduced in the selected lines over 70 generations, relative to controls, by approximately 32% in
males and 24% in females. However, part of this relative reduction was due to an increase in
growth rate of the controls populations, presumably an expression of adaptation to conditions in
our laboratory. After 50 generations of selection had elapsed, a considerable and increasing pre-
adult viability cost to faster development became apparent, with viability in the selected
populations being about 22% less than that of controls at generation 70 of selection.