EGG SIZE IN DROSOPHILA - STANDARD-UNIT OF INVESTMENT OR VARIABLE RESPONSE TO ENVIRONMENT - THE EFFECT OF TEMPERATURE

The volume and number of eggs laid by three Drosophila species (D. simulans, D. subobscura and D. phalerata) were measured over several seasons. Eggs were smaller and more numerous at higher temperatures. The total amount of resources invested in eggs increased with temperature, suggesting that there is no real physiological trade-off between egg volume and number. There was no consistent within-sample correlation between the two traits. The effect of temperature on egg volume was confirmed by comparing samples raised under identical temperature regimes up to the emergence of the imagos and exposed to different temperatures thereafter: the higher the temperature, the smaller the egg volume, indicating that egg volume in these species is more affected by environmental conditions than previously thought.