L. Nunney, THE RESPONSE TO SELECTION FOR FAST LARVAL DEVELOPMENT IN DROSOPHILA-MELANOGASTER AND ITS EFFECT ON ADULT WEIGHT - AN EXAMPLE OF A FITNESS TRADE-OFF, Evolution, 50(3), 1996, pp. 1193-1204
A selection experiment using Drosophila melanogaster revealed a strong
trade-off between adult weight and larval development time (LDT), sup
porting the view that antagonistic pleiotropy for these two fitness tr
aits determines mean adult size. Two experimental lines of flies were
selected for a shorter LDT (measured from egg laying to pupation). Aft
er 15 generations LDT was reduced by an average of 7.9%. The response
appeared to be controlled primarily by autosomal loci. A correlated re
sponse to the selection was a reduction in adult dry weight: individua
ls from the selected populations were on average 15.1% lighter than th
e controls. The lighter females of the selected lines showed a 35% dro
p in fecundity, bur no change in longevity. Thus, there is no direct r
elationship between LDT and adult longevity. The genetic correlation b
etween weight and LDT, as measured from their joint response to select
ion, was 0.86. Although there was weak evidence for dominance in LDT,
there was none for weight, making it unlikely that selection acting on
this antagonistic pleiotropy could lead to a stable polymorphism. In
all lines, sex differences in weight violated expectations based on in
trasex genetic correlations: Females, being larger than males, ought t
o require a longer LDT, whereas there was a slight trend in the opposi
te direction. Because the sexual dimorphism in size was nor significan
tly altered by selection, it appears that the controlling loci are eit
her invariant or have very limited pleiotropic effect on developmental
time. Iris suggested that they probably control some intrinsic, energ
y-intensive developmental process in males.