Critical weight for the induction of pupariation in Drosophila melanogaster:: genetic and environmental variation

Timing of puparium formation in Drosophila melanogaster is set by reaching a critical stage at which larvae attain the ability to pupariate. This critical stage is reached at a relatively constant size characterized by the mean critical weight, i.e. the weight at which 50% of surviving larvae pupate without further feeding. The mean critical weight might be affected by larval growth conditions. This hypothesis was tested by determining the mean critical weight in larvae raised at three temperatures and two food levels, for two isofemale lines from two populations. Pupariation probability is a function of larval weight. The two environmental variables affect pupariation probability and mean critical weight differently. Food level does not affect critical weight but affects weight-independent mortality; higher temperatures lead to a reduction of mean critical weight. Mean critical weight shows substantial differences between lines; the differences are maintained over temperatures. Genetic variation in mean critical weights has ecological and evolutionary implications.