Variability in diapause duration in the chestnut weevil: mixed ESS, genetic polymorphism or bet‐hedging?

Abstract

Within‐generation variability in diapause duration can be viewed either as a mixed Evolutionary Stable Strategy (ESS), a genetic polymorphism of pure strategies, or as bet‐hedging. Diapause variability expressed by a single genotype that maximizes mean geometric fitness at the cost of mean arithmetic fitness is a bet‐hedging strategy. Bet‐hedging differs from mixed ESS and stable genetic polymorphism of pure strategies because in these latter the expected pay‐offs for all phenotypes are equal. In insects, individuals with a prolonged diapause (long cycle) lose at least one reproductive opportunity and suffer lower survival before reproduction than those with a short diapause (short cycle). If long‐cycle individuals compensate this cost by better adult performance, the compensation leads to a trade‐off which could result in mixed ESS or genetic polymorphism of pure strategies since the overall fitness of the two morphs may be similar. In this paper, we show that in the chestnut weevil Curculio elephas adult performance, measured as sex ratio, longevity, weight, and realized fecundity of females, are similar in individuals emerged after one and two years. Long‐cycle morphs emerge slightly before short‐cycle ones but this eventual advantage for fertility probably does not compensate higher larval mortality and missed reproductive opportunity in long‐cycle phenotypes. Therefore, the cost associated with prolonged diapause cannot be completely compensated for by a better adult performance. From these results, and previous data, we conclude that variability in diapause duration cycle is better explained as bet‐hedging than mixed ESS or genetic polymorphism of pure strategies.