Has anyone ever seen a fig flower? Surely even if you really look for it, you will not find any of them. In fact, neither Linnaeus, the great Swedish botanist, could discover the enigma of fig flowers and when he described the species and gave him a scientific name (Ficus carica L.), he said the fig had no flowers! But then how does the fig reproduce himself and origins its delicious summer fruit; the fig?
A CASE OF OBLIGATE MUTUALISM
The flowers of the fig tree cannot be seen as they grow hidden inside the receptacle that supports them, the fig. They have developed a close relationship of mutualism with their pollinators so they don’t need to bloom externally offering sweet rewards. Indeed, each species of Ficus (including 750 species in family Moraceae) is pollinated by a unique wasp species (family Agaonidae; Blastophaga psenes in the case of the Mediterranean fig). It is a very complex case of coevolution between a plant and its pollinator in which neither species could survive without the other.
The mechanism of fig pollination works as a perfect gear. Female wasps are the first to visit the fig, where they arrive attracted by the smell of the mature female flowers. The female wasps possess special adaptations to penetrate the fig and achieve their ultimate goal: to leave their eggs inside. They have inverted teeth in the jaws and special hooks in the legs that let them to advance into the fruit. However, they have only one opportunity to deposit their eggs since most wasps lose their wings and antennae once they have entered the fig and therefore can no longer look for another. Once the eggs hatch, the wasp larvae feed on the contents of the fig. The male wasp larvae are the first to complete its development and when they reach sexual maturity, they seek female wasps, fertilize them and die inside the fig. The female wasps leave the figs a few days later, coinciding with the male flowers maturation and thus favoring that their exit will be carrying pollen. These fertilized and full of pollen wasps will look for a fig fruit again where to leave the pollen and eggs. Then the cycle begins again.
IS IT THE FIG ACTUALLY A FRUIT?
The fig is actually an infructescence (an ensemble of fruits that act as a single unit to facilitate the dispersion) with a special morphology called syconium. The syconium is a type of pear-shaped receptacle, thickened and fleshy with a small opening, the ostiole, that allows the entry of pollinators. Both male and female flowers (fig is monoecious) are together in the syconium, enveloped by bracts (white filaments found in the fig), but each one maturates in different time to avoid autopollination. Once the flowers are fertilized, the fruits originate within the same structure, thus flowers and fruits mix up.
WHERE DO THE FIGS COME FROM?
Who would have said that the fig tree would have a so complex fructification mechanism? In fact, the fig tree is native to Asia but is now naturalized in the Mediterranean since prehistoric times. There is evidence of its consumption and cultivation from the Neolithic. The fig tree is considered as one of the first plants cultivated by mankind. In spring it produces fertilized figs (breba), increasing its production with two harvests per year.
Main Ficus species grow in tropical climates. In temperate areas, some of this species were brought for its interest in gardening. Many cities have grown these giants in their public gardens because their dramatic appearance. They can reach up to 30 meters high and they develop aerial roots that end up reaching the ground acting as buttress that hold their weight. The have become unique elements of our urban landscape; such as in the Parque Genovés, Cadiz or the magnificent specimen of Ficus rubiginosa located in the Botanic Garden of Barcelona.
REFERENCES
- Byng W (2014). The Flowering Plants Handbook: A practical guide to families and genera of the world. Plant Gateway Ltd., Hertford, UK.
- Cruaud A, Cook J, Da-Rong Y, Genson G, Jabbour-Zahab R, Kjellberg F et al. (2011). Fig-fig wasp mutualism, the fall of the strict cospeciation paradigm? In: Patiny, S., ed., Evolution of plant-pollinator relationships. Cambridge: Cambridge University Press, pp. 68–102.
- Font Quer P (1953). Diccionario de Botánica. Ed. Labor
- Machado CA, Robbins N, Gilbert MTP & Herre EA (2005). Critical review of host specificity and its coevolutionary implications in the fig/fig-wasp mutualism. Proceedings of the National Academy of Sciences of the USA 102: 6558–6565.
- Ramirez WB (1970). Host specificity of fig wasps (Agaonidae). Evolution 24: 680–691.
- Serrato A & Oyama K (2012). Ficus y las avispas Agaonidae. ContactoS 85: 5–10.
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