Genetical Research

Correlated responses to selection on body size in Drosophila melanogaster

a1 Galton Laboratory, Department of Biology, University College London, Wolfson House, 4 Stephenson Way, London NW1 2HE, UK
a2 ICAPB, University of Edinburgh, Ashworth Building, Kings Buildings, West Mains Road, Edinburgh EH9 3JT, UK


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.

(Received August 12 1998)
(Revised December 15 1998)

c1 Corresponding author.
p1 Present address: Research Group in Evolutionary Biology, Institute of Evolutionary and Ecological Sciences, PO Box 9516, 2300 RA Leiden, The Netherlands.