WONG, THEODORE G.* AND DAVID D. ACKERLY. Department of Biological Sciences, Stanford University, Stanford, CA 94305-5020. - __How sensitive should plants be to cues? Theoretical studies of plastic reproduction schedules.__

We explore relationships among bet-hedging, phenotypic plasticity, and
the reliability of environmental cues with respect to the reproductive
allocation schedule in annual plants. The optimal schedule of biomass
allocation between reproduction and vegetative growth has been shown
to be bang-bang in constant environments and graded in unpredictable
environments -- a bet-hedging strategy. We summarize genetic-algorithm
studies which show that the optimal graded schedule is in fact a
weighted combination of the within-season fecundity-maximizing
strategies for each of the season-lengths possible in the environment.
Each season-length's contribution is a function of its probability, so
the degree of optimal gradedness directly reflects the degree of
environmental unpredictability. We then develop an analytical model of
allocational plasticity which compares fitness between the optimal
allocation given an environmental distribution and that given the same
distribution but conditioned on the state of an environmental cue. The
adaptiveness of plasticity is upper-bounded by an
information-theoretic measure of cue reliability: the mutual
information of the cue and the environmental state. Simulations
confirm that the probability that plastic allocators invade a
bet-hedging population increases with cue reliability and that the
form of the probability function is that of the mutual-information
function. Finally, we discuss the evolution of the complexity of
plants' environmental sensitivity and some ecological implications of
degrees of perceptual complexity.
**Key words:** bet-hedging, carbon allocation, environmental perception, genetic algorithms, phenology, phenotypic plasticity