THERMAL EVOLUTION OF PRE-ADULT LIFE-HISTORY TRAITS IN DROSOPHILA-MELANOGASTER

Replicated lines of Drosophila melanogaster were allowed to evolve in population cage culture at 16.5-degrees-C or 25-degrees-C for five yea rs. Their larval and pupal development times, larval growth rates, lar val critical weights for pupariation and pre-adult survival rates were then measured at both temperatures. Pre-adult survival showed evidenc e of adaptation of the lines to their thermal selection regimes, with each set of lines showing superior survival when tested at the tempera ture at which they had been evolving. Pupal periods were similar for a ll lines when growing at 16.5-degrees-C but, at 25-degrees-C, the low temperature lines had the longer pupal periods. Irrespective of experi mental temperature, low temperature lines grew faster and had shorter larval development periods than the high temperature lines. Larval cri tical weights for pupariation were higher in the low temperature lines at the low experimental temperature, and higher in the high temperatu re lines at the higher experimental temperature. The correlations betw een these traits induced by thermal evolution were in general differen t from or opposite to the genetic correlations found within a single t emperature.