Hypotheses: (1) Facultative species that occur in permanent and temporary streams can be locally adapted to their stream of origin or exhibit life-history plasticity. (2) Temporary stream populations respond to environmental cues signalling stream drying whereas permanent stream populations do not. (3) Sex-specific selection pressures imposed by seasonal time constraints imply that males prioritize early maturation whereas females maximize body size at maturity. Organism: Permanent and temporary stream populations of the alpine caddisfly Allogamus uncatus (Trichoptera) in the Val Roseg, Switzerland. Methods: We used a common garden experiment to test whether males and females from both stream types differed in their life-history response to combined changes in photoperiod (ambient vs. late) and hydroperiod (constant vs. drying). Results: Caddisflies exhibited life-history plasticity, although responses varied by time constraint cue and sex. Both sexes shortened development time in the late photoperiod treatments, but neither sex showed a stronger developmental response when exposed to both time constraint cues. Males emerged earlier and at a smaller size than females, and permanent stream males responded to stream drying. Females from both populations increased growth rate in the combined stress treatment, but only permanent stream females responded to hydroperiod stress with decreased growth rate and size at emergence. Temporary stream insects did not emerge earlier than permanent stream insects. © 2006 Lisa N.S. Shama.