How does egg size relate to body size in butterflies?

Although arthropod egg size is an evolutionarily and ecologically significant trait, there is still a poor understanding of the specific factors determining it. For butterflies there is evidence from an interspecific comparison that egg size is related to adult size, suggesting a morphological constraint. Using laboratory populations of the tropical butterfly Bicyclus anynana, we show that larger eggs produce larger hatchlings, and that there is considerable intra-populational variation in egg size. However, the correlation between egg size and female size is weak and explains only 1% of the variation found within a population; even development time is a slightly better predictor for egg size than female size. We conclude that there is no evidence that body size imposes a constraint on the evolution of egg size within butterfly populations. However, populations that have diverged in body size under artificial selection show correlated responses in egg size. Thus, correlations between body size and egg size may represent an emergent property, visible only when a large range of differences in body size is considered.