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Flower and Fruit Movements in Muntingia calabura: A Possible Mechanism for Avoidance of Pollinator-Disperser Interference

1984; Wiley; Volume: 16; Issue: 1 Linguagem: Inglês

10.2307/2387892

1744-7429

C. J. Webb,

Plant Ecology and Taxonomy Studies

Muntingia calabura produces a few flowers each day throughout the year. The flowers are usually borne in fascicles of two or three, and within each fascicle, four to nine days separate the sequential opening of individual 1-day flowers. Phyllotaxy is distichous on more or less horizontal branches and the tree architecture conforms to Troll's model. The continuous and regular growth pattern, with frequent branching, facilitates continuous initiation of supra-axillary flowering fascicles. Flowers are pollinated above the branches by bees, and fruit is dispersed from below the branches by bats. By elongation and erection of the pedicel, buds are raised into a flowering position, and following pollination, young fruit are lowered to a position for dispersal. As these movements of reproductive structures allow for pollination and dispersal simultaneously from different positions, it is suggested that for a continuously flowering species this may be a mechanism whereby pollinator-disperser interference is avoided. ALTHOUGH EXTENDED FLOWERING IS NOT UNCOMMON among tropical plants (Frankie et a/. 1974, Bawa 1983), continuous flowering, in the strict sense, is rare (Janzen 1967, Halle et a/. 1978). Continuous, as opposed to rhythmic, growth allows for continuous initiation of inflorescences but does not necessarily imply continuous flowering (Halle et a/. 1978). Likewise, continuous flowering does not preclude episodic fruit maturation. For those few species which continuously produce flowers and mature fruits, it is of interest to know, first, how continuous flowering is achieved, and second, what adaptations allow simultaneous pollination and fruit dispersal. MATERIALS AND METHODS Muntingia calabura L. (Elaeocarpaceae) is a small tree of disturbed successional habitats and is widely distributed in lowland Central America. The species has an unusual sexual system: all trees are similar, but flowers vary continuously in stamen number and ovary size within trees (Bawa and Webb 1983). The flowers are arranged in small fascicles, and those which open first in 2-flowered fascicles, and first or second in 3or more flowered fascicles, usually have a well developed pistil, few stamens, and they usually set fruit. Those flowers which open last in 3or more flowered fascicles usually have many stamens and a small pistil; these flowers usually abscise shortly after blooming (Bawa and Webb 1983). Data for this paper were gathered at Hacienda La Pacifica, five km northwest of Canias, Guanacaste Province, Costa Rica, during the 1981 dry season. At this locality, M. calabura is common in disturbed areas and along the margins of waterways and riparian forest. The climate and vegetation of the area are described in detail by Janzen (1967), Holdridge et al. (1971), Daubenmire (1972), and Frankie et a/. (1974). Initially, in order to observe the phenology of individual fascicles, five 3-flowered and three 2-flowered fascicles were tagged on a single tree and the days on which individual flowers opened were noted. During this study a sequence of bud, flower, and fruit movements was observed, so 10 more flowering fascicles were tagged on each of three trees. Two of these trees were in dry habitats and initiated mostly 2-flowered fascicles. The other tree, in a wet situation, had mostly 3-flowered fascicles. The orientation of each bud, flower, and young fruit relative to the branch and leaves was recorded daily for each of these 30 fascicles. Records were started when the first flower of a fascicle opened and continued until the tagged fascicle had finished flowering and the next fascicle on that branch had begun to flower. The rate of fascicle production, and its integration with vegetative growth, was documented for the three trees. Phyllotaxy, leaf fall, and branching pattern were