SEX DIFFERENCES AND FLOWERING PHENOLOGY IN THE COMMON FIG, FICUS CARICA L.

Abstract

The symbiotic relationship between fig plants (Ficus species) and their tiny pollinating wasps has fascinated biologists since classical times, when Aristotle and Theophrastus mentioned the connection between an abundance of wasps and a good fruit set in the common fig, Ficus carica L. The complex reproductive biology of Ficus species in general and of F. carica in particular has been described many times, and we will not repeat here details of floral morphology, pollination or insect structure and behavior (see Condit, 1947; Valdeyron, 1964, 1967; Galil and Eisikowitch, 1968a, 1968b, 1969, 1974; Ramirez, 1969, 1970, 1974, 1977; Hill, 1967; Galil, 1973, 1977; Storey, 1955, 1975, 1976; Galil and Neeman, 1977). After a description of some general features of the symbiotic relationship between Ficus species and wasps, we will concentrate on the differences between male and female plants of F. carica in their sexual performance and in the phenology of development of the syconia. The evolutionary origin of the separate sexes in F. carica and related species and the selective forces responsible for the characters of the various crops produced by the two sexes are considered in detail for the first time. The pollinators of the approximately 1000 species of Ficus are symbiotic wasps of the family Agaonidae (order Hymenoptera). The symbiosis is highly specific; Grandi (1929), Wiebes (1963), Hill (1967) and Ramirez (1970, 1974) have shown that in the great majority of investigated species in both the Old and New Worlds, each Ficus species is pollinated by one agaonid wasp which is confined to that species. The pollinator of F. carica, for example, is Blastophaga psenes L. In a few cases, one fig species hosts two wasp species or a wasp pollinates a few closely related Ficus species. The relationship between the reproduction of the tree and that of the insect is mutually obligatory, since pollen can be transferred to the enclosed female flowers only by the pollinator, and the wasps depend on the figs for their reproductive sites. The inflorescence of Ficus is a syconium, an enlarged urn-shaped peduncle bearing uniovulate pistillate flowers and staminate flowers on the inner surface. The female flowers reach anthesis several weeks before the male flowers of the same syconium. This pronounced protogyny prevents fertilization between pollen and ovules in one syconium. After copulation, adult female wasps become loaded with pollen and leave the syconia in which they developed. They then enter young receptive syconia by forcing their way between the bracts lining the apical orifice (ostiole). Once a wasp has entered a syconium, it cannot fly to another one. Within the syconium, a female wasp pollinates many female flowers and also inserts its ovipositor in the stylar canals of female flowers, in attempts to lay an egg in the ovule of each flower. The female flowers of a Ficus species vary markedly in style length; all female flowers are capable of being fertilized and producing seeds, but only short-styled flowers are suitable for egg laying. The longer styles prevent oviposition and many longstyled flowers are usually fertilized if a wasp carries pollen. The separation of