The basis of life-history plasticity in the tropical butterfly Hypolimnas bolina (L.) (Lepidoptera : Nymphalidae)

The common eggfly, Hypolimnas bolina (L.) (Lepidoptera : Nymphalidae), is a n adult-diapausing tropical and sub-tropical species that exhibits seasonal plasticity in adult body size. Here I investigated (a) whether size plasti city in this species is due solely to variations in rearing temperature, or whether photoperiod is also involved, and (b) whether rearing photoperiod affects the timing of ovarian development in adults. Individuals were cultu red at temperatures ranging from 21 degrees C to 30 degrees C, and under da ylengths of 11.5, 12.5 and 13.5 h in two separate experiments. Significant plasticity in juvenile developmental traits was detected in response to bot h variables, with cooler temperatures and shorter daylengths both leading t o decreased developmental rates and increased size at maturity. Although ju veniles grew more slowly with decreasing temperature, they grew faster with decreasing daylength. The timing of ovarian maturation was also related to rearing photoperiod; whereas 'long day' adults (13.5-h photoperiod) had gr avid ovaries after 10 days, the ovaries of 'short day' adults (11.5-h photo period) were either regressed or nearly so. These preliminary results sugge st that size variation observed in field populations of H. bolina may not b e wholly accounted for by variations in developmental temperature and, furt hermore, that photoperiod may be used by this tropical species as an enviro nmental cue for the seasonal timing of reproduction.