Correlated responses to artificial selection on body size in Drosophila melanogaster were
investigated, to determine how the changes in size were produced during development. Selection
for increased thorax length was associated with an increase in larval development time, an
extended growth period, no change in growth rate, and an increased critical larval weight for
pupariation. Selection for reduced thorax length was associated with reduced growth rate, no
change in duration of larval development and a reduced critical larval weight for pupariation. In
both lines selected for thorax length and lines selected for wing area, total body size changed in
the same direction as the artificially selected trait. In large selection lines of both types, the
increase in size was achieved almost entirely by an increase in cell number, while in the small lines
the decrease in size was achieved predominantly by reduced cell size, and also by a reduction in
cell number. The implications of the results for evolutionary-genetic change in body size in nature
are discussed.
Fitness variation in response to artificial selection for reduced cell area, cell number and wing area in natural populations of Drosophila melanogaster
