I have always been fascinated by a plant’s pollination strategy and how they aim to complete sexual reproduction. Some plants utilize wind, others water, and some rely on animals and insects to assist. Of the plants pollinated by animals or insects (“biotic agents”), some have co-evolved with a single species to complete reproduction. One of the most interesting mutualistic relationships belong to figs and fig wasps. Each one of the 750+ species of figs (Ficus sp.) has evolved alongside a specialized fig wasp, some for over 60 million years! It’s guaranteed that both the fig and fig wasp are receiving benefits from such a long term and intertwined relationship - and it’s all about reproduction! The fig wasp provides a pollen transfer service while also gaining access to a safe “nursery” to hatch the next generation of wasps.
As before, writing a Digging Deeper post has done just that… highlighting a topic I believe I have a decent understanding of takes me down a rabbit hole of research. “It is difficult to generalize about fig biology because of all the exceptions,” is a valid statement from Professor Wayne Armstrong of Palomar College. There are many different figs with differing reproductive parts which lead to different relationships with their specific fig wasp. For ease of understanding (both yours and mine), I am going to do exactly what Prof. Armstrong suggests against - I’m going to present a simplified example of a fig and fig wasp relationship. I urge you to check out Prof. Armstrong’s research here for the fascinating history of figs, beautiful slides displaying different figs and fig wasps, and because he takes the time to explain all the exceptions in his research: Sex Life of Figs: Coevolution of a Tree & Minute Wasp.
I BET YOU HAVEN’T SEEN THE FLOWERS OF A FIG TREE BEFORE…
You can make an educated guess on how a plant is pollinated by observing a flower’s features – these features are also called “pollinator syndromes.”
What happens when blooms on a plant are hidden and mysterious? Members of the Ficus genera don’t bloom in the way we traditionally envision flowers. With figs, the reproductive parts are inside-out. When you eat a fig you’re eating the inverted cluster of many tiny, fleshy flowers and seeds contained in a bulbous stem. This edible part isn’t even considered a true fruit as you can see in the cross-section photo of a fig below.
A female fig wasp crawls into an unripe fig’s small opening (ostiole) to deposit her eggs inside individual flowers. The flower responds by creating a gall-like structure to encapsulate the egg, where the egg matures into larvae. As the fig and larvae mature the male larvae hatch first then crawl around the inside of the fig fertilizing the females while the females are still in their galls. The male wasps are born without wings and their sole purpose is to mate and chew a tunnel to the outside of the fig, then they die. The female wasps from the same brood will hatch later, timed with the maturity of the male flowers when pollen is present. The female wasps file through the escape route their brother-lovers chewed for them and take flight to find another fig to lay their respective eggs. Fig wasps are so minute they ride the wind in search of the next fig. Hopefully, for the fig to achieve cross-pollination with another tree, the female fig wasp finds an unripe fig from another tree and crawls inside. The tight ostiole canal strips her of her antennae and wings and she will perish after depositing her fertilized eggs, but not before she inadvertently spreads the pollen from her birth-fig. And repeat – eggs hatch, mate, males chew tunnels, fertile females fly/float to the next fig, female wasp dies in next fig while depositing eggs and spreading pollen. It’s a wild ride, this circle of life! The graphic below from Encyclopedia Britannica walks you through each step of their life cycle.
There can be a lot of carnage involved in fig pollination and you might ask yourself – what happens to the dead wasp mom and the casualties of her young? Enter Ficin – an enzyme produced by fig trees to digest protein. Ficin dissolves the wasp’s body and nourishes the fig by reusing nutrients from the insect. What a carnivorous turn of events! Ficin is also used as a clotting agent in cheesemaking and is an effective replacement for calf rennet.
Before you consider giving up eating figs, as some vegans choose to do, know that fig trees commonly grown in home gardens, decedents of Common Figs (Ficus carica), are an exception to the rule. Leave it to mankind to interrupt a 60 million year tradition for cultivation. These cultivated varieties have been bred to not require cross-pollination with another fig, nor does it require a specialized fig wasp. (Don't worry - the “crunch” experience while eating a fig is not wasp parts… just seeds! Though insects are a common part of many diets across the world.)
This specialized relationship between fig and fig wasp is a great example of the efficiency and effectiveness of codependent evolution. Don’t you pity the plant that relies on the fickleness of wind and water for pollination? You can celebrate this relationship with a Ficus of your own, whether in your home or your landscape. Here’s a list of figs we offer at Painters Greenhouse during our regular season (fig wasps not included in purchase):
Rubber Tree (houseplant) – Ficus elastica
Weeping Fig (houseplant) – Ficus benjamina
Fiddle Leaf Fig (houseplant) – Ficus lyrata
Audrey/Banyan Fig (houseplant) – Ficus benghalensis
Creeping Fig (houseplant) – Ficus repens
‘Brown Turkey’ Fig (edible) – Ficus carica