Data for: Predictable local adaptation in butterfly photoperiodism but not thermal performance along a latitudinal cline

In seasonal environments, organisms must synchronize their life cycles to
conditions favorable for growth and reproduction. Because season length
varies geographically, local adaptation should arise in traits that
regulate phenological responses. Geographic photoperiodism clines are
well-known, but comparable studies on thermal performance are equivocal
and often overlook non-linear responses. Therefore, we examined local
adaptation in plastic responses to both photoperiod and temperature along
a 752 km latitudinal cline, by comparing four Swedish populations of the
butterfly Pieris napi. Using a common garden design, we estimated (1)
photoperiod response curves for diapause induction and (2) thermal
performance curves for development and growth rates. We show that
differences in photoperiodism follow the expected geographical pattern,
where diapause is induced at longer daylengths in northern populations
(where growth seasons are short and summer days long). However, population
differences in thermal performance curves were small and seemingly
idiosyncratic, without clear clinal patterns. Photoperiodic responses
appear to evolve more readily than thermal responses, highlighting
photoperiodism as a key driver of local life cycle synchronization.