The evolutionarily stable (or ESS) emergence schedule for males of uni
voltine butterflies is analysed in an environment in which the female
emergence schedule fluctuates stochastically between years. The ESS em
ergence curve, computed using the mutant invadability criterion, is sh
own to be the one that maximizes mean logarithmic lifetime mating succ
ess in the population in which it dominates. If males have accurate in
formation about the female emergence schedule within each year, their
emergence curve would evolve to the one predicted by a deterministic g
ame model. The male emergence curve would then shift between years, cl
osely following year to year changes in the female emergence pattern.
If, instead, males have uncertainty about the female emergence schedul
e, the ESS male emergence curve becomes broader than the one predicted
by the deterministic game model and will not track the between-year f
luctuation of female emergence well. In a special case, we show how th
e between-year variation of mean emergence date, the variance of emerg
ence date, the sexual difference in mean emergence dates (protandry) a
nd the between-year correlation of mean emergence dates of both sexes
should change with the degree of accuracy of information available to
males.