Weight accumulation
Compared to the results for development rate, the effects of photoperiod
treatment on weight were weaker, and quite population-dependent
(analysis of deviance; population × treatment
χ210=22.5; p=0.012). The only
population that showed a significant difference in final size between
the control treatments was Öland, where constant exposure to short days
produced pupae that were approximately 10% heavier than did constant
exposure to long days (within-population planned contrast;
t567=4.01, p=0.001). This difference was not detectable
at any earlier life stage. In contrast to the results for development
time, changes in photoperiod regime during development did not appear to
drive final size; instead, pupal weights tended to correspond to the
initial photoperiod experienced (Fig. 4; Fig. S2). Females were larger
than males across all populations (analysis of deviance; sex
χ21=142.1; p<0.001); unlike
the late effects of photoperiod, the sex difference was detectable as
early as the third instar, and was increased further in later stages.