The Queens subjects.

The Queens subjects.


The fig tree has for long been considered the Queen of trees. Botanists and biologists confirm that, worldwide, something like 1,200 vertebrate species depend primarily on figs to survive. It is this diversity of life dependant on the fig tree that gives it the distinction of being the Queen of trees.  A study in late 1990’s showed that ten per cent of all birds and six per cent of all mammals depend on figs as part of their diet– (see Who eats figs? Everybody)

Why are fig trees so important to the survival of wildlife? The answer is simple; fig trees have multiple cycles of fruiting with some fig species producing flowers and figs year-round. This means a year-round supply of food for birds and mammals is available. In lean times, a fruiting fig tree can be a godsend for starving animals. (see A job for conservation’s keystone cops).

There are over 750+ species of fig trees in the tropics with most being pollinated by a single species of Fig wasp. The fig trees depend heavily on these wasps to survive. The wasps pollinate the flowers ensuring that the fruits form and the next generation of fig trees can spread their shade over a new patch of the forest. The wasps use the figs as hosts to lay their eggs in. The female wasps enter the fig through a ‘gate’, feed on the figs and make their way down a tubular structure to the flower where they unload their payload of pollen from pollen sacs in the abdomen onto the flower to pollinate it. The wasps use pollen as a bribe to the Queen in exchange for her services as an incubator for her eggs. Fossil evidence showed that wasps used the same method of pollination 65 million years ago with microscopic analysis revealing striking similarities in the pollen sacs of the fossils and their descendants.

Female Fig wasp showing her ovipositor.

The female fig wasps live for about a day and each wasp species can only lay its eggs inside the flowers of its specific fig partner. The winged females have to squeeze through the narrow gate to gain access to the flower and in doing so she rips out her wings and at times even bursts her abdomen. This epitomizes the theory of the ‘struggle for existence’ with the females making the ultimate sacrifice while making their way to their fleshy graves to ensure the survival of the species. Once the female lays her eggs, she dies within the fruit itself. As soon as the eggs hatch, the males break out of their casings and eat into the casing of the females, not to release them, but to mate with them. The males live a short life and after they have mated they begin to die. The drive to perpetuate the species fires up their instinctive response and the males begin to eat at the fruit to help the females break out.

Female fig wasps try to make their way past the ‘gate’.

I had been observing a particular fig tree outside my classroom window in college for quite some time during boring lectures on Hepatitis B. I noticed that the same set of fruits had been on the tree well over a month and a half ago. When I checked the next day, almost all the fruits were unripe, with barely a handful reaching more than 8mm in breadth. Oddly, none of them showed any signs of being pollinated or having fig wasps in them. I had seen this fig tree fruit sometime in February, (roughly 7 months ago), and here it was, with unripe fruits still hanging in clusters on the tree, the characteristic mat of fruits below the tree being nowhere in sight. Surely housekeeping wasn’t so diligent that they wouldn’t let a single fig touch the ground?
(watch: https://youtu.be/8fpKDtLjvaI)

I took a fig early next morning off the tree and with great curiosity split it open. I was surprised to see a number of females fly out from this unripe fig. The fig wasn’t even ripe, it was still hard. Yet the wasps had somehow gotten to it. But if the figs had wasps in them, why weren’t there any ripe fruits on the tree. The White Cheeked Barbets had stopped visiting now, and the squirrels only visited the tree on a bright sunny morning. The cacophony on the fig tree had stopped with the Rosy Starlings, our European migrants being nowhere in sight this time. Last year there were hundreds on the fig tree. 

Fig wasps inside a raw fig.

Why did this happen this time around? I would assume it was due to the fig wasps dying out this season owing to the blistering heat the city faced in March and April with the mercury hitting the roof. When the wasps were exposed to temperatures between 25°C and 38°C and to a various levels of humidity, the lifespan of all four species fell steadily as the temperature rose. By 36°C, the lifespan of three of the species had fallen to just two hours. In the wild this severely reduces the time a wasp has to find a fig of the right species, pollinate it and lay its eggs. In the 1990s, fig-wasps in northern Borneo went locally extinct after a severe drought, and in Florida they disappeared when a hurricane wiped them out. Both species survived thanks to their ability to disperse tens of thousands of kilometers in such short life spans.

While all of this sounds like the species can recover easily… with sustained rises in global temperature; the life span of these wasps is expected to take a hit with a marked change in fruiting patterns that may also affect other creatures over time. The failure of the figs ripening this year seems to be a clear indication of this. And the number of figs that show the presence of the wasps also suggests a decrease in populations of the figs. Only time can tell if the figs will ripen or if they will fall to the ground unripe like they have been doing so for the past few weeks and if the Queens subjects live to pollinate another set of flowers.

Do check out this amazing video to get a better understanding of what exactly happens during the course of a wasp’s life. (PS: 52:00 mins long, so watch it if you are really keen on knowing what a wasp does--- 

References:

·         Jevanandam, N., Goh, A.G.R. & Corlett, R. 2013. Climate warming and the potential extinction of fig wasps, the obligate pollinators of figs. Biology Letters 9: X-X.  Published online March 20, 2013 doi: 10.1098/rsbl.2013.0041

·         http://www.sanctuaryasia.com/magazines/features/10208-no-climate-for-fig-wasps.html

·         The Influence of Temperature on the Reproductive Success of a Fig Wasp and Its Host Plant Areej Alkhalaf, Rupert J. Quinnell, and Stephen G. Compton