Natural Sciences Science & Philosophy

The Wonder of the Fig

The title may be a misnomer. On the first look, it suggests that this is a story of the fig (“anjeer”) alone, when it is a story of the Ficus genus that has more than 850 species in it that are collectively known as figs, and its 80 million year old soul-mate, the wasp, a tiny insect. The title stands correct, as we shall see, because most of our story will take place inside the fig, a collection of tiny flowers enclosed within a spherical shape that we mistake for a common fruit. Despite being a story of a plant and an insect, the story has elements of trust and betrayal, of selfish motives and altruistic outcomes, of deception and manipulation, and of subtle strategies and tactics. And all of these elements will be played out in their lurid details by players who are, for all practical purposes, totally lacking consciousness.

And this story stands as a testament to the ingenious work of scientists and researchers, whose tireless toiling, disciplined approach, and ingenuity make such discoveries possible. It involved not just passively looking at the figs, but slicing them and observing them. It required a systematic sampling from a large number of trees, from particular heights, and from particular seasons of the year. It required them to observe the wasps wriggling inside the figs, documenting these tiny insects, accurately drawing them, counting and measuring them, and all of this had to be followed by extensive classification. And while all of the data was being documented, it also required coming up with highly imaginative and intelligent hypotheses and testing them against the new found data, and thus constantly trying to decrease the gap between the hypotheses and the reality.

And in the case of this article, the story also stands as a testament to the efforts of people like Richard Dawkins who show great enthusiasm and devotion in the endless task of keeping the general public aware of the difficult-to-grasp but awe-inspiring facts of nature. This article’s direct source is his book ‘Climbing Mount Improbable’ which a critic aptly called “a beautiful, barnstorming, thunderclap of a book”.

Let us begin our story now, the story of the fig, something we recognise as a common fruit (“anjeer”) and one that we love to relish (see Figure 1 below), but of all the 850 species of the genus Ficus, only about 2 are edible by us. Although the story takes a general view of them all, it would not be too inaccurate if we keep in mind the edible fig (see Figure 1 below) while we play this story in our mind.

Fig picking (Courtesy Demand Farming Australia) http://www.demandfarming.com.au/prosperityfarmingsystems.html

Figure 1: Inside the fig. (Image links to source)

Inside our fig

The fig fruit, as I mentioned earlier, is not a fruit at all. In fact, if we think of a garden as a vast collection of flowers with different pollinators and insects and parasites roaming around, then the fig fruit is an ‘enclosed garden’, for it has all of those elements. But I will frequently call it as a “fruit” in the story for the sake of simplicity. Just like a Sunflower is not actually a flower but hundreds of small flowers packed into a mass bed giving the ‘appearance’ of a single flower, the fig fruit is a collection of hundreds of female and male flowers with a variety of insects and pollinators roaming everywhere inside it. When you slice open a fig what you see is hundreds of tiny flowers, both male and female and if you use a lens you may also get to see the tiny insects making a living inside it.

Evolution of the fig

But this complex structure of the fig did not arise spontaneously out of nowhere. Like all living things, it evolved. Picture the fig in your mind. Now, imagine looking at the differences in its structure as we slowly go back in time. If we go back a few centuries or a millennium, the essential structure will remain the same and the fruit will still be easily identifiable. But turn to the scale of millions of years and the wonder unfolds itself- initially through our journey back in time the fig’s small entrance will slowly open up and grow in a bigger hole. Again after rewinding a few million years more the entrance hole will enlarge considerably and the spherical fig will now resemble a cup with the inner layer populated with tiny flowers. Go back a few million years more than that and the cup keeps getting more and more shallow and at one point the small florets will actually be on the “outside” part of the shallow flattened cup.  Further back, the little florets become more distinct until they are no more together at all and there is no such thing as a fig fruit. This is evolution of the fig in reverse, and it will be helpful in connecting the dots from the story that follows ahead.

Also keep in mind that figs reproduce sexually (almost all do). As I said, there are tiny male flowers inside the fig that produce pollen, which have to be carried by pollinating insects to the female flowers that are also present inside the fig. The ‘pollination’ is said to be complete once the pollen is deposited in the fertile female flowers which can continue to become an actual seed with the potential of growing into a new fig tree. But the fig plant will not simply pollinate its female flowers with pollen from the same fruit or fruit of the same plant; on the contrary, it takes great efforts to avoid such self-pollination. They always prefer to mate with flowers from other plants. This ensures healthy offspring as incest leads to amplification of undesirable genetic traits. That is why some flowers will produce nectar just to attract a bee and dust it cleverly with its pollen which is now carried on the bee’s body to other distant flowers during the bee’s course of travel.

The wasp, soul-mate of the fig

Ceratosolen capensis the pollinator of Ficus sur on a finger to illustrate the small size of fig wasps (Image courtesy Figweb: http://www.figweb.org/Interaction/Who_pollinates_fig_trees/index.htm)

Figure 2: Ceratosolen capensis the pollinator of Ficus sur on a finger to illustrate the small size of fig wasps. (Image from www.figweb.org. Click for source)

And now it is time to introduce the other protagonist in the story- the wasp. It’s a tiny insect; indeed the fig wasps are much smaller than other well-known wasps (see Figure 2 alongside). These fig wasps are the sole pollinators of the figs, and they both are utterly dependent on each other. Almost all of the 850 species of figs have their own special species of wasps for pollination. Take away the wasps, and the figs will have absolutely no way to reproduce, take away the figs and now the wasps have no way to exist.

Let us take a look at a typical life-cycle of the wasp. All wasps are born inside the fig fruit, under the tiny female flowers located deep inside it. The tiny male flowers are typically located at the end of the fruit, towards its exit (also works as entrance). The wasps will grow under female flowers that are already pollinated by some earlier wasp, and the infant wasps will feed on the seed before turning into adults and breaking out of the egg-like capsule. Inside the fig fruit or our ‘enclosed garden’, the male will hatch first and search inside for female wasps. When he finds a female wasp, he will chew his way through the ovule wall (ovule is a part of the fig’s female flowers and all wasps are born there) and he will mate with the still unborn virgin wasp.

A female fig wasp emerging from a gall.  (Photo Credit: Richard van Noort) Source: http://www.bloggero.info/aggression-prevents-better-part-valor-fig-wasps-18838

Figure 3: A female fig wasp emerging from a gall. (Photo Credit: Richard van Noort) Source: Bloggero Science News

She then emerges from the capsule and now her own journey begins (see Figure 3 alongside). What happens next varies from species to species but here is a typical story. The female now looks for male fig flowers inside the fruit that produce pollen, and brushes all that pollen systematically on her body and stores them safely in her breasts. Notice how careful and deliberate is her action storing the pollen. Instead of being a passive agent like the bee, she actively brushes them on her body and stores them in her custom-built pollen-carrying sockets on her breasts.

Now laden with this precious fig pollen, the female leaves the fruit and goes into the sunlight for the first, but also the last time. The males never leave the fruit and never get to see the light of the day and their life cycle is over inside the darkness of the fig itself. Usually the males will help the female wasp to escape the fruit by boring a hole in the entrance/exit.

Courtella wardi ovipositing. Image source: http://www.figweb.org/Interaction/Who_pollinates_fig_trees/index.htm

Figure 4: Courtella Wardi oviposting. Image via figweb.org. Click for source.

Once outside in the open air, it is now the female’s task to search for the right kind of fig which is in the right phase of its life and ready to receive pollen. Once she finds such a fig, she will struggle and wiggle her way through the entrance of the fig, and most often she will lose her wings in the painful process. But she doesn’t mind losing the wings as she won’t need them further. Once inside the fruit, she now carefully deposits the pollen in all of the female flowers inside the fruit and completes the act of pollination. Later she will deposit her own eggs in some of them (see Figure 4 alongside), not all, and die inside the fruit once the task is done. Also, keep in mind that the pollinated female flowers in which she has deposited her eggs will not grow into seeds as her own eggs will devour the seed. Only those female flowers that she pollinated but did not burden with her own eggs will continue to make a seed.

But why doesn’t she simply load all of the pollinated flowers with her eggs so that maximum number of her own wasp children will be born? Why care for the seeds of the fig? And with questions like these we will now step in the realm of evolutionary conflicts and strategies. It is only by being aware that the questions exist at all will we be able to find the answers, and later have a chance to marvel at them. The depth of our answers will be determined by the depth of our questions, and we will have to ask ourselves a few crucial questions if we are to understand the poetry and drama hidden in nature.

Evolution

“Nothing in biology makes sense except in the light of Evolution” said the biologist Theodosius Dobzhansky, so let us know a few things about it. A gene is a small sequence of DNA, and they are directly inherited from parents to children without any change (except in case of mutation). Specific genes will directly account for specific traits (mostly it is actually interaction among genes or multiple genes culminating in a single effect, but it is okay to go ahead with the view of “one gene-one trait” in our minds). The traits may be physical; there may be a gene that makes the fig red and another gene that makes it green. But only the colour which helps the fig tree to reproduce will be passed on to the next generation, and that colour will become the norm. The genes will also directly control behavior of the wasp too, and we may have a gene that makes the wasp better at transporting the pollen while another gene that makes it worse. But in the long run, only the efficient pollen carrying genes will remain because only they will have children to further carry those genes. The mutations in the genes may be completely random, but the selection by environmental factors will always be non-random; natural selection will select only the fit. And genes have no consciousness, hence no capacity for foresight, and they tend to propagate or mutate not because they “want to” but just because that’s the way things ‘are’; water spreads on the floor not because it wants to but because that’s the way it ‘is’.

Evolution or specifically natural selection does not act on an entire species or even on individuals, but only on genes, and this is a crucial insight that owes a lot to Richard Dawkins. Natural selection selects among genes, not individuals or species even if it is the individual that lives or dies, so all genes can be given the adjective “selfish”,  as they will compete for survival (again, not without any inner deliberation)even if some gene results in an altruistic behavior.  But can “selfish” genes result in altruistic traits? Let’s see.

Questions and answers

Getting back to our question, why doesn’t the female wasp simply load her eggs in all of the pollinated flowers? Remember that wasps can grow only in pollinated flowers but then those flowers don’t develop into seeds; it’s a win-lose situation. But again, why does the wasp care when apparently it has no concept of caring?

Why be so friendly to the fig and provide some concession? It is because it has been discovered that when all the pollinated flowers are laden with wasp eggs, and hence as the fig tree “realises” that it will have no seeds from this particular fig, the fig tree will simply drop that fig on the ground, thus killing it and everything inside it. It did not just kill the wasps, it also killed genes that make wasps completely “selfish” and load all pollinated flowers with eggs like their mother did. It is one of the few “intimidating” tactics of the fig tree. A direct revenge for betrayal, is it not? But don’t be misled by my use of anthropomorphic words like “wants, revenge, desires, prefers” because the fig tree is indubitably unconscious and the wasp’s tiny brain has no capacity for such concepts. But given a period of millions of years, only the really efficient genetic traits will survive. A fig tree that doesn’t mind losing her figs to wasps will not pass her “lenient” genes but a fig tree that has genes to drop useless figs will pass her “revengeful” genes to the next generation. Hence in the long run, it will appear to our human eyes that the fig tree is indeed “conscious” or “aware” when in fact it is literally mindlessly obeying its genes.

Dioecious figs

Now that the stage is set for grand evolutionary spectacle, we can start tackling more challenging and interesting conflicts, and they begin when we move from ‘monoecious’ fig trees to ‘dioecious’ fig trees. A few but crucial things are different in the dioecious trees.

In the earlier example we talked about figs that contain within them both male and female flowers. But dioecious fig trees will have all its male flowers on one tree and all female flowers on other tree. So there will be a male tree and a female tree, and male trees will make figs that contain only male flowers and female trees will make figs that contain only female flowers. But just like our earlier story, the wasp’s eggs cannot grow in male flowers because those eggs feed on the pollinated female flowers; so how come male trees are able to attract wasps at all? Hang on to this question for a while. A further difference in the dioecious trees is that if a wasp lays her eggs inside a female flower, the eggs cannot grow in them and the seed will not provide food to the eggs (in total contrast to our earlier story of monoecious figs where the wasp eggs feed on the growing seed of the pollinated female flowers). So, a wasp can’t deposit her eggs in male flowers, and her deposited eggs are not allowed to grow in female flowers? Then how do wasps continue to exist at all?

Here’s how.  To attract the wasps and keep their race alive, the figs of the male trees also contain “pseudo-female flowers” that don’t actually do anything for the fig tree (directly). All that those pseudo-female flowers do is provide food for the baby wasps, mimic the structure and scent of the real-female flowers, and nothing else. But there’s a catch- just like the real female flowers of the monoecious figs, these pseudo-female flowers will provide food only if they are pollinated by wasps! Even if they are practically sterile and pollination is seemingly useless, these pseudo-female flowers will not let baby wasps grow in them if their mothers don’t actually pollinate them. Why so? We’ll return to this question soon.

First let us understand conflicting ‘wants’ (not in a conscious sense, but a Darwinian sense) of both the figs and the wasps:

The wasps only want to enter the male figs that contain the pseudo-female flowers, because only in them its eggs will be able to grow. The wasp has no immediate profit from entering female figs because its eggs will not be allowed to grow in the seeds (unlike the monoecious trees). The figs, on the other hand, want the wasps to enter both the male and female figs, not just the male figs, so that pollen will be carried from male to female figs for pollination. Let us remind ourselves again that evolution has absolutely no foresight at all, and the wasps will want to enter only the male figs even if it means that in the future both races will go extinct. The wasp does not care for the future, because it cannot care. So despite such conflicting wants, why don’t the species go extinct? The answer lies in evolutionary stable strategies, which are unconscious and work only in the present, but if they are stable, they will sustain the players playing them. This is how it works out:

The dioecious fig trees make it extremely difficult for the wasp to distinguish between male and female figs, by becoming more and more similar to each other. They even start to give out similar scents to increase the wasp’s confusion. All of this just to confuse the wasp and make it more likely that it will visit both male and female figs equally. Now we must ask ourselves, what if there is a “selfish” male fig with “manly” features that does not bother look similar to female figs? It will certainly attract more wasps initially, and thus pollinate more than the rest. But what would happen in the long run? This “selfish” fig will give birth to wasp children whose genes teach them to identify similar “manly” trees, and they will choose only these trees to pollinate. But these “manly” trees have only “pseudo-female flowers” and cannot grow seeds, and hence these “selfish” fig genes will die out by themselves. So in the long run, only mutually co-operating fig genes will survive that bother to try harder and harder to reduce the differences between male and female figs.

Now we are ready to tackle the earlier question too; the final one within the scope of this article but not the final one when it comes to the real grand story of figs and their wasps.

Once the wasp enters inside the male fig, why do the pseudo-female flowers provide food for the baby wasps only after it is pollinated by the wasp? Even when it is patently obvious that pollination is useless for pseudo-female flowers because they are, well, pseudo, and don’t produce seeds. As with all questions, the answer lies in evolutionary strategies.

Suppose there are two genes for the male figs- one is “fussy” and the other is “easy-going”. The “fussy” gene makes it necessary for the wasps to pollinate the pseudo-female flowers before providing food, while the “easy-going” gene will provide food to the baby wasps even if the wasp mother fails to pollinate the pseudo-female flowers first.

In the first and initial runs, the “easy-going” male tree will give birth to more wasps because it gives food to all eggs under its pseudo-female flowers regardless of the fact that they are pollinated or not, while the “fussy” male tree will give birth to lesser number of wasps because it provides food only after the wasp succeeds in pollinating its pseudo-female flowers.

But watch out, the genes of the “easy-going” tree have given food to wasps whose parents were apparently bad at pollinating! And hence their children will carry the same traits. They will fail like their parents in the act of pollination, perhaps because they carry “lazy” genes or whatever, but in the long run they will fail a lot to deposit pollen in the real-female flowers. Whereas the “fussy” male tree has given food and birth only to wasps whose parents had succeeded in pollinating the pseudo-female flowers, and hence their children are better at pollinating. Quality more than makes up for quantity, and hence we can expect to see only the “fussy” fig genes around. This kind of natural selection is termed as ‘vicarious selection’ where the pseudo-female flowers act like simulators who only want the best pilots to fly the actual planes i.e. pollination of real-female flowers.

The Greatest Show on Earth

All the questions we faced and the answers that we discovered are only a small part of the true life-cycle of fig and its wasps. But I hope this story gave us a glimpse of the subtle intricacies and the vast scale of evolution; at some point the line between species blurred because of fig genes that help wasps more directly than it helped its owner and vice versa, and I hope it gave us an idea about how various random mutations will be filtered out in the long-run so that only the efficient mutations will remain, and how time, natural selection, and genes shape us and every living thing around us.

Remember that there are still many dramas occurring inside and around the fig- there are parasites and again parasites of those parasites (hyper-parasites) in the fig and they too have their own stories, some of which require direct mathematical assistance to figure out the answers. We concerned ourselves only with pollination but the seeds also need to be dispersed and that’s another larger story altogether concerning animals from ants to elephants. Some of the most perplexing questions deal with the structure of pseudo-flowers and female wasps and their answers are just as tantalizing. Entire careers and websites have been made around the story of fig alone (see sources). But again I hope our brief inquiry into the world of figs has helped us in gauging the almost infinite immensity and intricacies of the evolutionary show that is being constantly played on our Earth.  A show that has been going on for billions of years on the stage of our planet (and perhaps on others too), a show in which we humans have entered only very recently, but we are special because only we have the potential to discover and appreciate the subtlety, complexity and wonder of Life. And if there is unbound wonder hidden in the story of the fig alone, imagine the infinite wonder of millions of species permeating every corner of our Earth. The noble human quest for the “complete truth”, if there be such a thing, thus may seem endless. But if it seems so, it can only be extremely uplifting and eternally motivating to know that we will always have greater mysteries and grander discoveries to look forward to.

And let us end our story with the words of Darwin himself,

“There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.”

Very helpful and awesome documentary:

http://www.youtube.com/watch?v=sxJdweffxEE

Sources:

1) ‘Climbing Mount Improbable’, Richard Dawkins, 1996
2) www.figweb.org

Additional reading (apart from sources):

1) http://www.futurity.org/science-technology/34-million-year-old-fig-wasp-fossil-found/

About the author

Gaurav D. Somwanshi

Gaurav D. Somwanshi.
Born: 2nd May, 1990..

Alumnus, IIM Lucknow (2013) & GEC Aurangabad (2011)

Email id: gaurav.somwanshi@iiml.org
gauravsomwanshi@gmail.com

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