Life history plasticity: Influence of photoperiod on growth and development in the common blue butterfly

The daylength experienced by a larva provides information about the progression of the season, so that plasticity in growth and development with photoperiod might serve as an adaptation allowing efficient timing relative to the favorable part of the season. In an experiment with Polyommatus icarus it was found that shorter daylengths, indicating less time available until the season ends, resulted in faster development from hatching to adult eclosion. From hatching and into the earlier part of the final instar, larval mass increased approximately exponentially with time, but the rate of growth during this phase was not affected by photoperiod. Both the later part of the final instar and pupal development proceeded more rapidly in shorter daylengths. The decrease in total development time did not reduce female final size, measured as pupal mass, whereas males became somewhat smaller. Males developed slightly faster than females (protandry) and were heavier than females in the longer daylengths but lighter in the shorter daylengths. The observed lack of a trade-off between development time and adult size in females is discussed in the light of life history theory of optimal age and size at maturity.