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.