Ficus - Fig Pollination and Fig Fruit

Fig Pollination and Fig Fruit

Many fig species are grown for their fruits, though only Ficus carica is cultivated to any extent for this purpose. The fig fruits, important as both food and traditional medicine, contain laxative substances, flavonoids, sugars, vitamins A and C, acids and enzymes. However, figs are skin allergens, and the sap is a serious eye irritant. The fig is a false fruit or multiple fruit, in which the flowers and seeds grow together to form a single mass. The genus Dorstenia, also in the figs family (Moraceae), exhibits similar tiny flowers arranged on a receptacle but in this case the receptacle is a more or less flat, open surface. Propagating figs can be done by seeds, cuttings, air-layering or grafting. However, as with any plant, figs grown from seed are not necessarily genetically identical to the parent and are only propagated this way for breeding purposes.

Depending on the species, each fruit can contain up to several hundred to several thousand seeds.

A fig "fruit" is derived from a specially adapted type of inflorescence (an arrangement of multiple flowers). In this case, it is an involuted, nearly closed receptacle with many small flowers arranged on the inner surface. Thus the actual flowers of the fig are unseen unless the fig is cut open. In Chinese the fig is called wú huā guǒ (simplified Chinese: 无花果; traditional Chinese: 無花果), "fruit without flower". In Bengali, where the Common Fig is called dumur, it is referenced in a proverb: tumi jeno dumurer phool hoe gele ("You have become the dumur flower").

The syconium often has a bulbous shape with a small opening (the ostiole) at the outward end that allows access to pollinators. The flowers are pollinated by very small wasps that crawl through the opening in search of a suitable place to lay eggs. Without this pollinator service fig trees could not reproduce by seed. In turn, the flowers provide a safe haven and nourishment for the next generation of wasps. This accounts for the frequent presence of wasp larvae in the fruit, and has led to a coevolutionary relationship. Technically, a fig fruit proper would be one of the many tiny mature, seed-bearing flowers found inside one fig – if you cut open a fresh fig, the flowers will appear as fleshy "threads", each bearing a single seed inside.

Fig plants can be monoecious (hermaphrodite) or gynodioecious (hermaphrodite and female). Nearly half of fig species are gynodioecious, and therefore have some plants with inflorescences (syconium) with long styled pistillate flowers, and other plants with staminate flowers mixed with short styled pistillate flowers. The long flowers styles tend to prevent wasps from laying their eggs within the ovules, while the short styled flowers are accessible for egg laying.

All the native fig trees of the American continent are hermaphrodites, as well as species like Indian Banyan (F. benghalensis), Weeping Fig (F. benjamina), Indian Rubber Plant (F. elastica), Fiddle-leaved Fig (F. lyrata), Moreton Bay Fig (F. macrophylla), Chinese Banyan (F. microcarpa), Sacred Fig (F. religiosa) and Sycamore Fig (F. sycomorus).

On the other hand the Common Fig (Ficus carica) is a gynodioecious plant, as well as Lofty fig or Clown fig (F. aspera), Roxburgh Fig (F. auriculata), Mistletoe Fig (F. deltoidea), F. pseudopalma, Creeping Fig (F. pumila) and related species.

The hermaphrodite Common Figs are called "inedible figs" or caprifigs; in traditional culture in the Mediterranean region they were considered food for goats (Capra aegagrus). In the female fig trees, the male flower parts fail to develop; they produce the "edible figs". Fig wasps grow in Common Fig caprifigs but not in the female syconiums because the female flower is too long for the wasp to successfully lay her eggs in them. Nonetheless, the wasp pollinates the flower with pollen from the caprifig it grew up in. When the wasp dies, it is broken down by enzymes (Ficain) inside the fig. Fig wasps are not known to transmit any diseases harmful to humans.

When a caprifig ripens, another caprifig must be ready to be pollinated. In temperate climes, wasps hibernate in figs, and there are distinct crops. Common Fig caprifigs have three crops per year; edible figs have two. The first (breva) produces small fruits called olynth. Some parthenocarpic cultivars of Common Figs do not require pollination at all, and will produce a crop of figs (albeit sterile) in the absence of caprifigs or fig wasps.

There is typically only one species of wasp capable of fertilizing the flowers of each species of fig, and therefore plantings of fig species outside of their native range results in effectively sterile individuals. For example, in Hawaii, some 60 species of figs have been introduced, but only four of the wasps that fertilize them have been introduced, so only four species of figs produce viable seeds there and can become invasive species. This is an example of mutualism, in which each organism (fig plant and fig wasp) benefit each other, in this case reproductively.

The intimate association between fig species and their wasp pollinators, along with the high incidence of a one-to-one plant-pollinator ratio have long led scientists to believe that figs and wasps are a clear example of coevolution. Morphological and reproductive behavior evidence, such as the correspondence between fig and wasp larvae maturation rates, have been cited as support for this hypothesis for many years. Additionally, recent genetic and molecular dating analyses have shown a very close correspondence in the character evolution and speciation phylogenies of these two clades.

Recently, molecular techniques including the combined use of microsatellite markers in combination with mitochondrial sequence analyses have suggested that the one-to-one relationships between figs and their pollinators may not be as strict as once believed The discovery of multiple genetically distinct, cryptic wasp species paired with individual fig species supports this concern, particularly considering that not all cryptic species are sister taxa and thus must have experienced a host shift at some point. These cryptic species lacked evidence of genetic introgression or backcrosses indicating limited fitness for hybrids and effective reproductive isolation and speciation.

The existence of cryptic species suggests that neither the number of symbionts nor their evolutionary relationships are necessarily fixed ecologically. Fifty percent of fig species host multiple wasp pollinators thus are not tied inextricably to any single symbiont. On the other hand, species of wasps have been shown to pollinate multiple host fig species While the morphological characteristics that facilitate the fig-wasp mutualisms are likely to be shared more fully in closer relatives, the absence of unique pairings would make it impossible to do a one-to-one tree comparison and difficult to determine cospeciation.