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 pr ogression of the season, so that plasticity in growth and development with photoperiod might serve as an adaptation allowing efficient timin g relative to the favorable part of the season. In an experiment with Polyommatus icarus it was found that shorter daylengths, indicating le ss time available until the season ends, resulted in faster developmen t from hatching to adult eclosion. From hatching and into the earlier part of the final instar, larval mass increased approximately exponent ially with time, but the rate of growth during this phase was not affe cted by photoperiod. Both the later part of the final instar and pupal development proceeded more rapidly in shorter daylengths. The decreas e 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 female s in the longer daylengths but lighter in the shorter daylengths. The observed lack of a trade-off between development time and adult size i n females is discussed in the light of life history theory of optimal age and size at maturity.