• Phuong

Fig Newtons and Co-Evolution

Updated: Feb 5

**Trigger Warning: if you are a fan of figs I’m obligated to warn you that this article may change your opinion about them. Don’t get me wrong, the science is actually really interesting, but there can definitely be repercussions to this knowledge!**

I don’t mind a good fig bar, and fig ice cream is even better! In fact, I had some amazing fig ice cream recently when my curiosity got the better of me--what is a fig really? Is it a berry? Are figs even fruit? Turns out, they’re not! And if that’s surprising to you (I was definitely surprised to hear this), then hang on tight because it’s going to get a whole lot wilder from here.

Figs are actually classified as inflorescences, which are a group or cluster of flowers arranged on a stem. There are several examples of inflorescences that you might have encountered before, and many of them have clustering flowers arranged in different patterns. In fact, a common inflorescence that you are probably familiar with are sunflowers! Sunflowers are actually composed of a cluster of smaller flowers arranged on a stem with petals radially surrounding the cluster. So figs are really just a cluster of flowers that are encased in a bulb! Now you might be wondering how these flowers ever get pollinated if they’re encased in a shell and protected from the environment. This is where nature gets creative.

The only access the fig cavity has to the outside world is through a tiny bract-lined opening at the apex of the fig, called the ostiole. It is here that a pollinating fig wasp gains access to the florets. Yes, wasps are the primary pollinators of figs! Specifically, queen wasps. These queen wasps have flat heads and thoraxes that enable them to crawl through the fig cavity, depositing eggs and pollen picked up from other figs. After laying her eggs, the queen wasp dies within the fig providing nutrients to the flowers. In return, the flowers produce nutrients to feed her offspring when they hatch.

Upon hatching, the wasps mate with each other, and male wasps create an opening for the female wasps to leave the bulb and continue the pollination process. The male wasps are blind and wingless, and they stay within the fig for their entire lives. Crazy right? Typically wasps die very quickly, usually around 24 hours, after laying eggs so this whole process occurs relatively quickly.

This wasp-fig dependency is called coevolution. Generally, coevolution is when two species rely on each other to evolve. Examples of coevolution include predator/prey relationships, plants/pollinators, and parasite/host relationships. As crazy as the fig-wasp relationship sounds it’s actually not uncommon in nature. The fig-wasp relationship has been around for millenia, with reports that suggest it has been around since the time of dinosaurs. Of course, this doesn’t make it less disturbing.

Interestingly, some species of fig plants have evolved to ‘trick’ wasps. About half of figs are "monoecious", meaning each tree produces both male and female flowers. The others are "dioecious" and have two kinds of figs on separate plants: "gall figs" with male and female flowers, and "seed figs" with female flowers only. In dioecious trees, the stalks of the female flowers are too long for the wasp to lay eggs in them so only the male flowers are able to host the offspring. However, the female flowers have evolved to give off a scent that mimics male flowers and tricks the wasps into attempting to lay eggs in them! This way, the female flowers would benefit from the extra pollen carried by the wasp, but the wasp gets no benefit from this interaction as their offspring would die. A Nature article was recently published in 2016 by Hossaert-McKey et. al. attempts to address this trick that the female flowers have evolved to perform.

Now the question you’ve all been waiting for: do you eat wasp carcasses when you bite into a Fig Newton? Like many things in science, the answer to this is: it depends. Some figs don’t have seeds and therefore don’t require pollination to grow. Fortunately for us, most (if not all) commercially cultivated figs don’t tend to have seeds. So your Fig Newton is likely wasp-free. However if you decide to munch on a non-commercially cultivated fig, then you might be less lucky. It’s okay though, figs can still be delicious and the wasps provide extra protein!

Fig tree image from gogreenbk.org

Thanks to the wasps’ short lifecycle, they ensure that fig trees bear figs all year round to provide many wildlife food. And I have these wasps to thank for the delicious ice cream that I had the other day, which I will still continue to eat regardless of this new nugget of science knowledge.