Gender Variation and Expression of Monoecy in Juniperus phoenicea (L.) (Cupressaceae)

Abstract

Variation of gender expression and cone production is described quantitatively for Juniperus phoenicea L. populations in southern Spain and Morocco. The species is monoecious, but most populations showed a dichotomy of gender expression at flowering, with predominantly "male" and predominantly "female" plants and few "monoecious" individuals, a functionally subdioecious breeding system. The proportion of female plants in the Spanish populations ranged from 31% (R. B. Donana) to 40% (Cda. Sabinas, 1988) and did not exceed 10% in Morocco. Most plants with femaleness values < .40 failed to set full-sized seed cones or produced very small crops. Individual plants showed a significant constancy of gender expression in consecutive years. Most inconsistencies in sexual behavior involved transitions between the male and female expressions and their respective "inconstant" conditions. Between-year variations in seed-bearing cone production largely reflected changes in female flowering gender of the individual plants; years with large crop production were characterized by increases in average female gender expression for a given gender category and, as a result, a greater percentage of the population producing female cones. Plants differing in gender expression showed no significant differences in size. Male plants always produced fewer than 10 female cones per crop, and inconstant males rarely exceeded 200 female cones; female plants usually had crop sizes above 100 cones, except in the seasons of cone crop failure. Individual plants also differed in annual shoot growth, but these differences were unrelated to both gender expression and cone production in the previous season. Differences among populations accounted for 52% of total variance in female cone size, while the effect of the individual plant accounted for 26%; only 22% was attributable to within-plant variation. A nested model with gender category as the main effect and plant as a nested effect accounted for 88% of total variation in five cone characteristics, but gender effect accounted for ≤ 2%.