But this is where it gets interesting. In general, Fusarium prefers moist environments (although it can live in hot, arid regions as well). So, it would make sense that chilis that are found in dry environments should produce less capsaicin, and more offspring, than their more arid, Fusarium-threatened relatives.

To test this hypothesis, researchers at the University of Washington first sampled chili plants along a 185 line in Bolivia that naturally varied in water availability. What they found was that even in the dry environments there were chilis with high amounts of capsaicin, but they only accounted for about 20% of the population. However, as the environment became wetter, the percent of high-capsaicin producing plants increased, and at the extreme end of the spectrum, in the moistest environments, all of the plants were capsaicin producers.

 To test the relationship between water-efficiency and number of offspring, the researchers designed a controlled experiment in which identical populations of chili plants were grown under similar experiments and then exposed to either a normal, or water-stressed, environment. The results confirmed that plants with higher amounts of capsaicin produced fewer offspring. Although the direct link between capsaicin and water-efficiency has not yet been determined, it is evident that production of the compound comes at a fitness cost to the plant. 

So the next time you bite into a really hot chili, consider that fact that what you are really experiencing is an ancient arms race between a  pepper and a fungi – and that the chili you are eating sacrificed its fitness for your spiceness.

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