L. Nunney et W. Cheung, THE EFFECT OF TEMPERATURE ON BODY-SIZE AND FECUNDITY IN FEMALE DROSOPHILA-MELANOGASTER - EVIDENCE FOR ADAPTIVE PLASTICITY, Evolution, 51(5), 1997, pp. 1529-1535
The reaction norm linking rearing temperature and size in Drosophila m
elanogaster results in progressively larger flies as the temperature i
s lowered from 30 degrees C to 18 degrees C, but it has remained uncle
ar whether this phenotypic plasticity is part of an adaptive response
to temperature. We found that female D, melanogaster reared to adultho
od at 18 degrees C versus 25 degrees C showed a 12% increase in dry we
ight. Measurements of the fecundity of these two types of fly showed t
hat the size change had no effect on lifetime fecundity, regardless of
the adult test temperature. Thus the phenotypic plasticity breaks the
usual positive correlation between body size and fecundity. However,
at a given temperature, early fecundity (defined as productivity for d
ays 5 through 12 after eclosion at 25 degrees C and days 7 through 17
at 18 degrees C) was highest when the rearing and test temperatures we
re the same. The early fecundity advantage due to rearing at the test
temperature was 25% at 18 degrees C and 16% at 25 degrees C, a result
consistent with the overall phenotypic response to temperature being a
daptive. This conclusion is further supported by the finding that the
temperature treatments resulted in a trade-off between early fecundity
and longevity, a trade-off that parallels the known genetic correlati
on. Another parallel is that both the temperature-induced and genetic
effects are independent of total fecundity. By contrast, within the te
mperature treatments, the phenotypic correlation between early fecundi
ty and longevity was positive, illustrating the danger of assuming tha
t phenotypic and genetic correlations are similar, or even of the same
sign.