Sexual Dimorphism and the Annual Flowering Pattern in Jacaratia Dolichaula (D. Smith) Woodson (Caricaceae) in a Costa Rican Rain Forest

Abstract

Flowering phenology and other aspects of reproductive biology were investigated to determine the extent of differences between male and female plants of Jacaratia dolichaula (Caricaceae), a small tree of neotropical lowland rain forests. The study revealed a number of differences between sexes. (1) The sex ratio was 1.08 males: 1 female, though the "opertional sex ratio" ranged from 10.0:1 to 1.4:1 during the blooming period. (2) The male trees tended to mature earlier than females, as indicated by the frequency distribution of size classes; however, there were no differences in growth rates between sexes over a 1—yr period. (3) The flowers were strongly dimorphic; male flowers had a long corolla tube and nectar, but female flowers had free petals and no nectar. Pollination was presumed to be effected by intersexual mimicry of nonhomologous flower parts. (4) The population flowered once per year for °9 mo from October to June, but with a distinct peak in February. Female trees tended to begin flowering later in the season than males, and had individual flowering periods less than half as long as males. (5) Females produced fewer flowers per year than males by a factor of °20. (6) Although the diameter at breast height and the size of the flower crop were correlated in both male and female trees, the correlation was stronger in males than in females. However, in females, the correlation between trunk size and fruit production was better than for flower production. (7) Female trees flowered less frequently than males, and there were marked fluctuations in fruit production between years. (8) There was no variation in sex expression of individual trees in 4 yr. The differences in the reproductive features of male and female plants are discussed in the context of sexual selection, dynamics of the pollination system, and energetics.