The Adaptive Significance of Sexual Lability in Plants Using Atriplex canescens as a Principal Example

Experimental studies demonstrate that up to 2096 of the individuals of Atriplex canescens and other species of the genus can alter their sexual state from one season to the next.Approximately 5% of the A. canescens individuals changed from an exclusively pistillate phenotype t to an 5% w the in ndividuals c hanged their primary sexual emphasis, e.g., phenotype or vice versa.Another y staminate addition, ntly stami inate, 10% of the population changed from a unisexual state to a monoecious state in which siis and equal in number (or vice versa).In Atriplex oat pis sex change occurred in response to three stresses: an unusually cold winter, drought, and p ced under stress, pistillate individuals are significantly more likely to change sex than staminate individuals.The ability to change sex appears to When pla or heavy seed set.o confer a survival advantage to the individual.Plants which change sex also -to begin reproducing earlier than pistillate MEN while producing as many seeds as pistillate plants do.T advantages in the population studied.Recent ecological studies indicate that androecious (male) and gynoecious (female) individuals of several dioecious plant species exhibit partial niche separation; J. L. Harper has termed this pattern the Jack Sprat effect (Onyekwelu & arper, 1979).The most commonly reported manifestation of the Jack Sprat effect is the segiduals along strong environmental gradients.For example, Freeman et al. (1976) Showed that the sexes of five dioecious plant Species of the intermountain region of the westетп United States segregated along gradients of Water availability or salinity.Androecious plants