Pollinators and Herbivores Influence the Evolution of Chemicals Emitted by Fig Plants in Different Ways

Plants produce Volatile Organic Compounds (VOCs) to communicate with insects. By releasing their scent, they can attract pollinators to their flowers, but other insects can use this same scent to identify plants to feed upon. Yang Yang and colleagues in Shanghai and Xiamen studied how Figs, Ficus, have evolved their scent to attract pollinators but confuse antagonists. Their research, published in the Journal of Systematics and Evolution, shows that as few as two volatile chemicals could supply sufficient information for pollinators to identify figs.

The opportunity to attract one set of insects and distract another comes from how the two groups interact with plants. Plants and pollinators can co-evolve to form a specialist relationship, and this explains how fig-pollinating wasps have specific chemical communication with fig plants. Herbivores are often more generalist. They like eating fig plants but can eat others too, so they don’t specialize to the same degree.

As the captions suggests a row of fig trees in a possibly French garden. I was anticipating the haze to come from the trees, but the AI artist has quite reasonably decided that the perfume would come from a large number of incense burners. — A haze of perfume over a row of fig trees in the style of Maney. Image: Midjourney.

The need to deliver reliable information through chemicals yet also confuse other insects means there are two evolutionary pressures on plants. For pollinators, plant fitness increases with the reliability of the signal. For herbivores, plant fitness improves when the signal works as misinformation.

Yang and colleagues tracked earlier research on the chemical profiles of figs. They were able to identify 244 VOCs from 45 Ficus species. Of these, the split was almost half and half between VOCs that were only produced by one species and VOCs that were produced by two or more species.

There are some limitations to the study, but this might have more effect on understanding how plants confound attackers than on how they attract pollinators, as Yang and colleagues write: “It is notable that our models only qualitatively utilized empirical data, without considering the concentration of each VOC. Although this disadvantage must prevent unraveling the effects of mixture of multiple VOCs on confusing antagonists, it may have limited impacts on pollinator host identification, because pollinating wasps can respond to the specific attractant even at extremely low concentration.”

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Yang, Y., Zhang, Y.-Y., Zhang, Y., Chen, S., Li, Q.-Y., Wang, R. and Chen, X.-Y. (2022) “Selection to attract pollinators and to confuse antagonists specializes fig‐pollinator chemical communications,” Journal of Systematics and Evolution. https://doi.org/10.1111/jse.12908