干旱区生态环境知识资源中心

Pupal period is highly variable in Epirrita autumnata (Lepidoptera, Geometridae) lasting from about one to over three months. We aimed to find proximate and ultimate explanations for the high variability, including the possibility that variation in eclosion time represents a diversified bet-hedging strategy, patterns of variation in pupal period, both among and within populations, were analyzed in several common environment experiments, including one with a half-sib design. We further assessed possible selective forces on eclosion date and its variance using an empirical simulation model.

Latitudinal among-population differences in pupal period were shown to have a genetic basis. Within populations, there was a considerable among-sibship variance in this trait that suggests high heritabilities of pupal period. The environmental component of the variance was unlikely to result from a deterministic reaction norm, neither adaptive nor constraint-based, and may thus represent a type of variance on which a bet-hedging strategy can be based. Importantly, there were significant among-sibship differences in the variance itself, and a significant sire effect on offspring variability in the half-sib design. This suggests a possibility for the variance in pupal period to be selected for as such, and for increased random environmental variance (a bet-hedging strategy) to evolve via natural selection.

We assumed that seasonal changes in night temperatures and predation rate determine the optimal timing of adult flight period in E. autumnata. Results of modeling suggested that there are apparently hat fitness profiles in relation to eclosion date, which is the probable reason for maintenance of high genetic diversity in pupal period. Unpredictable temperature during adult flight period has a potential to select for high variance in eclosion dates, although the selective pressure appears to be weak. Genetic variance in variance of pupal period may thus be largely selectively neutral in the studied system.