The Secret Life of Figs - August 11, 2010
Jeff Schalau, Associate Agent, Agriculture & Natural Resources
University of Arizona Cooperative Extension, Yavapai County

In previous installments of the Backyard Gardener, I have discussed how some organisms form mutualistic relationships: associations between organisms of two different species in which each member benefits. One example is nitrogen fixing bacteria that live in the root nodules of legumes (plants in the pea and bean family) where they convert atmospheric nitrogen into plant-available nitrogen. Another is the relationships between 80% of the world’s plants with mycorrhizal root fungi which enhance phosphorus availability and disease resistance in those plants. In each case, the plant provides carbohydrates to the bacteria or fungi in return for nitrogen, phosphorus, and other benefits.

Many readers are likely aware that figs are pollinated by very small wasps. Figs are filled with microscopic flowers and, when fertilized, produce the small seeds that go crunch when you bite into a fig bar. The flowers are not visible from the outside of the fig. Fertilized female wasps crawl into unripe figs which contain unfertilized flowers to lay their eggs, and in doing so, carry pollen from fig to fig, thus pollinating the flowers and producing those crunchy seeds. Where the female wasp lays an egg, the flower forms a gall rather than a seed. This does not pose a problem for the fig though – the wasp has pollinated the flowers and the seeds will form to ensure a future for the fig trees.

Back to the developing wasps, male wasps emerge from their galls first and fertilize the females before they emerge. Next, the females emerge from their galls and collect pollen from the fig flowers before emerging from the fig to visit and pollinate other fig flowers. In this manner, the figs are pollinated and the wasps have a protected place to breed. This is another classic example of mutualism – or so it seems. Less than 5% of the time, the female wasp neglects to collect the pollen and simply departs to lay her eggs in another fig. If the fig is not pollinated, it will not produce seeds and may be aborted by the tree. Wasp eggs in the aborted figs do not develop thereby providing negative feedback and preventing that individual wasp’s reproduction.

Most of us are aware of edible figs and even some of the varieties (Mission, Brown Turkey, Kadota, etc.). If you’ve been to the tropics or are an indoor plant lover, you may be aware of the over 700 known fig species. Each fig species partners with a few species of these small, pollinating wasps to produce seeds. But the plot thickens: not all fig species abort the unfertilized fruit with equal regularity. The fig species that impose strict punishment instill meticulous pollination habits in their wasp populations by aborting figs with greater frequency. Other fig species are more accepting of poor pollination habits and abort fewer unfertilized figs which perpetuates lazy pollination behavior in those wasp populations.

Sneaky wasps are one thing, but some fig species can be downright spiteful. Half of the known fig species have evolved a pollination system that unfairly punishes wasps by luring them into specialized female-only flower pouches that accept pollen but kill the wasps’ young. While these fig species have figured out how to deceive the wasps, as far as we know, the wasps have not yet figured out a way to reciprocate. It’s a dog-eat-dog world out there – even among figs and pollinating wasps. Cheaters abound in nature as well as human society - and sometimes they go unpunished.

I hope you’ve enjoyed this foray into the world of fig pollination. Of course, there is the off chance that you didn’t enjoy the technical rambling – but, if that were the case, you wouldn’t have read this far. Regardless, I credit my inspiration to Science News. If you’d like to learn even more about nature’s cheaters, see the July 31, 2010 Science News article Nature’s Recourse: How Plants and Animals Fight Back When Deals Go Sour by Susan Milius.

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Arizona Cooperative Extension
Yavapai County
840 Rodeo Dr. #C
Prescott, AZ 86305
(928) 445-6590
Last Updated: August 3, 2010
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