Mjo. Watson et Aa. Hoffmann, ACCLIMATION, CROSS-GENERATION EFFECTS, AND THE RESPONSE TO SELECTION FOR INCREASED COLD RESISTANCE IN DROSOPHILA, Evolution, 50(3), 1996, pp. 1182-1192
The way populations respond to selection can be altered when populatio
ns are acclimated prior to selection. To examine this possibility, the
responses of replicate lines of Drosophila melanogaster and D. simula
ns to selection for increased resistance to cold were compared. Flies
were selected without hardening or after they had been hardened by hol
ding them at 4 degrees C for one hour. The selection response in both
species was much greater when Hies were not cold-hardened. Cold resist
ance in both sers of selected lines reached a plateau after a few gene
rations. Surprisingly, continued selection for increased resistance re
sulted in decreasing levels of resistance. This decrease was no longer
evident after selection had been relaxed for a generation, suggesting
cross-generation effects. The magnitude of the cross-generation effec
ts increased with additional generations of selection. Cross-generatio
n effects were also detected for fitness components. Relaxing selectio
n for a generation increased fecundity, weight, viability, and develop
ment time. Comparisons of relaxed lines and control lines indicated th
at only fecundity was influenced by selection. Both sets of selected l
ines had a lower fecundity than control lines. Crosses between control
and selected lines and among replicate selected lines indicated that
this decrease in fecundity was not associated with inbreeding. The dir
ect and correlated responses to selection for cold resistance can ther
efore be influenced by acclimation and cross-generation effects.