INTRAPOPULATION SEX-RATIO VARIATION IN THE SALT GRASS DISTICHLIS-SPICATA

In many dioecious plant populations, males and females appear to be sp atially segregated, a pattern that is difficult to explain given its p otentially high costs. However, in asexually propagating species, spat ial segregation of the sexes may be indistinguishable from superficial ly similar patterns generated by random establishment of a few genets followed by extensive clonal spread and by gender-specific differences in rates of clonal spread. In populations where a significant fractio n of individuals are not flowering and gender cannot be assigned to th is fraction, apparent spatial segregation of the sexes may be due to d ifferential flowering between the sexes. We confirm reports that flowe ring ramets of the clonal, perennial grass Distichlis spicata are spat ially segregated by sex. We extend these studies in two fundamental wa ys and demonstrate that this species exhibits true spatial segregation of the sexes. First, using RAPD markers, we estimated that at least 5 0% of ramets in patches with biased sex ratios represent distinct geno types. Second, we identified a RAPD marker linked to female phenotype (eliminating the possibility that gender is environmentally determined ) and used it to show that the majority of patches exhibit significant ly biased sex ratios for both ramets and genets, regardless of floweri ng status.