Fecundity, and the Relation of Egg Weight Variation to Offspring Fitness in the Speckled Wood Butterfly Pararge aegeria, or Why Don't Butterfly Females Lay More Eggs?
Females of the speckled wood butterfly, P. aegeria L., lay eggs that decrease in size over the oviposition period. By weighing all of the individual eggs laid by 2 females and rearing the larvae from these eggs individually it was assessed whether there was any correlation between egg weight and egg survival, larval survival, larval development time and pupal weight. None of these fitness variables was correlated with egg weight. Since females could have increased their fecundity by some 25% if they had laid small eggs only, this raises the question as to what factor can be responsible for counteracting the maximization of the number of eggs laid by the speckled wood. Since several lines of evidence indicate that time is a limiting factor for ovipositing butterflies, and it is well known the butterfly females devote considerable time to locating suitable habitats and host plants for the deposition of their eggs, it is hypothesized that butterfly females have to make a trade-off between maximizing the number of eggs laid and the time spent searching for suitable oviposition sites for each individual egg. In consequence the factor responsible for counteracting the evolution of unbridled fecundity in the speckled wood might be classified as a kind of parental care.