Conclusions
Phenotypic plasticity can produce a high degree of adaptive match between phenotype and environment, but it is not without limits. For example, fitness hinges on whether future environments can be accurately predicted, and whether phenotypes can be induced and developed in time for the predicted environmental conditions to arrive (DeWitt et al., 1998). When the fitness costs of producing a mismatched phenotype are asymmetric (in this case: if it is more risky to attempt diapause on short notice than to attempt non-diapause development on short notice), it may be adaptive for the induction mechanism to become asymmetrically sensitive to environmental signals as well (Friberg et al., 2011). Here we extend this perspective from the diapause/nondiapause switch to include larval development rate and body size. Development rate inP. aegeria responded to photoperiod early in life (long before the diapause decision itself is finalized), which allowed for large differences in the final phenotype (i.e. age at maturity). However, development rate also continually responded to changes in photoperiodic information, following the same asymmetric pattern of sensitivity as the diapause decision. As photoperiod changes across the season, current development rate affects future exposure to photoperiodic signals, hence development rate forms part of a developmental cascade shaping the growth trajectory of an individual. In contrast to development rate, body size regulation appears to diverge late in life, and did not show the same flexible response to changes in photoperiod. These results underscore how co-adapted phenotypes like the diapause/nondiapause alternative pathways can evolve from suites of traits that share a cue (photoperiod), but have different ontogenies.