Evolutionary ecology of butterfly fecundity

Butterfly reproductive traits vary considerably between and within species. Examples of those traits include the number of mature eggs at eclosion, the lifetime number of eggs laid, egg production rate, size of eggs, the difference between potential and realized fecundity, oviposition rate and the degree of egg clustering. Egg-laying is not independent of other life-history traits, behaviours and habitat use, and it is subject to evolutionary change. Most butterflies are capital breeders since they mainly use nutrients from reserves that were accumulated during the larval stages for their reproductive output. Nitrogen is the limiting factor. However, the female’s nutrient budget can be complemented by adult feeding and by male spermatophore donations. Size of spermatophores relative to male body size depends on the mating system, and consequently varies among species. Potential fecundity is determined by larval resources, whereas realized fecundity also depends on biological and physical factors. Hence, realized fecundity is clearly condition-dependent with a significant contribution from female body size and condition. Trade-offs between the number and the size of eggs have attracted much attention. Because butterflies are ectotherms and more particularly heliotherms in the adult stage, temperature can have a strong effect on their fecundity. Temperature affects growth rate and development time, and hence the nutritional reserves built up during the larval stages, but it also affects flight activity and oviposition time-budgets. Fecundity also depends on the allocation and reallocation of material to reproductive versus somatic tissue. There is experimental evidence for the increase of fecundity from flight-muscle-derived nutrients. Trade-offs between fecundity and mobility need to take into account such physiological dynamics. Although knowledge on butterfly fecundity has improved significantly over the last decades, it still remains a challenge to predict what will happen to fecundity patterns under anthropogenic environmental changes.