A Unique Symbiotic Relationship

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Strangler Figs & Fig Wasps

One of the prime goals of all organisms is the survival of its species. The fig tree and the fig wasp have that connectedness in our ecosystem that achieves that goal. Neither organism can exist without the other. Data has confirmed that this mutualistic relationship has survived for 70 Million years.

The Fig Tree

The fig tree (Ficus genus) is part of the Moraceae family, a family of flowering plants comprising about 38 geniuses and over 1100 species. They are located in tropical and subtropical regions of the world. Fig tree genus, has the largest number of species, 850, of the Moraceae Family.

The one that draws the most attention is the, visibly unique, strangler fig. Strangler fig is a generic name for a number of tropical and subtropical fig plant species that employ a strangling/parasitic technique to achieve their survivability.

A common question about the strangler fig is, “How does the strangling start and what happens to the host tree?”   Well, let’s first look at the strangler fig life cycle.

Strangler fig roots strangle a cypress tree. Photo by Royce Bair, 123rf.com.

It starts when a strangler fig seedling is deposited in a crevice or partially enclosed area of a host tree by wildlife or weather. To help insure success, the fig seed is “sticky.” The enclosure the seedling is in contains moisture from rain, fallen organic materials, bugs and other living organisms.

To illustrate, we’ll choose a bird as our seedling depositor and the palm tree with its “boot”:

The bird lands in the boot of a palm tree, eats some of the bugs in the boot and defecates. His “poop” contains a fig seed. With the right conditions in our boot, sunlight partially filtered by the canopy, the seedling begins to grow. The first stage of its growth is as an air plant, an epiphyte. Epiphytes grow on other plants and do not negatively affect its host tree. The seed gets sustenance from material in the boot or absorbed from the air. It begins its growth, slow at first. Eventually the epiphyte becomes parasite.

Fig roots from the seed grow into the host palm tree and draw water and nutrients. In its early stage, small branches, leaves and several inflorescences also known as our figs (syconium), grow. Fig trees are classified as fast growing. Aerial roots shoot to the ground, where they quickly dive into the soil and anchor themselves. They soak up the water and nutrients, crowding out the root system of the host. The fig tree secures more life giving sustenance, while depriving the host tree. The roots grow wide and strong. The strangling occurs not just from below but also from above the infestation seed. The roots that go up the tree start growing branches and leaves, eventually getting above the palm leaves and blocking out sunlight for the struggling host. In time there are not enough palm leaves to capture the sun for photosynthesis process and natural production of food ceases for the host tree.

The strangler fig sentences its host tree to a nearly inescapable death. The process is usually a long one. Death is inevitable but timing is completely arbitrary. The variables in question are numerous. It’s impossible to say how long the host will live. In general, an older host tree could take a shorter time to die, while small, weak or sick trees could die within a season. A healthy large host can live 200 years past the time of infestation. There have been many discoveries of centuries old strangler fig trees with only hollowed out remnants of its host.

The Fig Wasp

To complete our lifecycle review of this profoundly unique symbiotic relationship we look at the fig wasp.

First let’s put the fig wasp into perspective as we did with fig tree. The wasp is part of the Superfamily Chalcidoidea, which encompasses approximately 18 families of wasps, 470 geniuses and over 500,000 species estimated worldwide. One of the families is the Agaonidae family, the fig wasp.

An important point, all fig trees are pollinated by fig wasps. But there is a unique specialized relationship with certain groups of fig wasp and fig tree, approximately 600 species of fig wasp and 600 species of figs trees are instinctively connected to each other.

According to Britannica.com, “Each species of fig wasp pollinates only one species of fig tree, and that fig tree species allows that one particular wasp species to lay her eggs in its flower. This extraordinary diversity of coevolution between figs and fig wasps has become so profound that neither organism can exist without the other.”

The process begins when its mutual partner fig tree fig syconium has developed to the point that it is ready to accept pollination and the laying of fig wasp eggs.

At that time the syconium releases a scent to attract a pregnant fig wasp. Ready to lay her eggs, she picks up an irresistible scent and makes a “bee” line (sorry for that), a “wasp” line from her home fig tree to its mutual partner fig tree. Our pregnant female fig wasp only has 2 – 3 days to live. She finds her home escape tunnel. As she is leaving her home, she picks up pollen from the stamen (male flower), and exits the syconium. Arriving at the other tree, she enters the syconium. Upon entering she loses her wings and part of her antenna. This process drains her energy. Finding her first flower she begins to lay an egg in the ovule of the flower (Pistil). She continues to lay eggs until, totally spent, she dies.

Let’s move forward a period of time. The male wasp is the first wasp to hatch. He eats his way out of the gall structure, has no eyes or wings. Using his sense of smell, searches for the female eggs in their home the syconium. The male wasp, locates a female egg and mates, before they hatch. He continues mating with other eggs. His last duty is to create an escape tunnel for his mates in the syconium wall, and then he dies.

The pregnant female wasp hatches, eats her way out of the gall structure, and emerges. Again her life cycle is 2 – 3 day long. In a short time, hopefully, she picks up that enchanting aroma from the syconium of another fig tree and the process continues. Fortunately as one fig tree’s figs are eaten and new fig syconium begin to grow, another fig trees figs are ripe and ready to continue the supply of food and the survival of its species continues. That’s why this mutual symbiotic relationship is a keystone in South West Florida’s ecosystem.

 

By J. M. Scalisi
Florida Master Naturalist