Chilli pungency: Tracking it back

In a second study of chilli pungency in the wild, Tewksbury, Levey, and colleagues summarize current views of the evolution of Capsicum species, and report on several years of surveying chilli populations in the semiarid countryside of southeastern Bolivia, the region where their spiciness may have originated. They found mixed populations of pungent and non-pungent plants, and pungency seems to be associated with higher elevations and possibly greater stress.

There are around 25 species in the genus Capsicum, only some of which produce the pungent chemical capsaicin and its relatives, collectively called capsaicinoids. The 2,000 or so domesticated varieties come from just 3 to 5 of these species. DNA analysis indicates that the oldest surviving species of all is a non-pungent one, and that pungency evolved in its descendents, perhaps the first being Capsicum chacoense in dry mountainous areas of Bolivia or Peru, which may then have spread more widely into the plains and the wet Amazon basin and given rise to the species that humans later cultivated. Capsicum annuum, the source of our most common domesticated varieties, is a moisture-loving species from Brazil.

The scientists studied wild populations of Capsicum chacoense and two other species thought to be among the oldest, C. baccatum (whose domesticated varieties are known as aji) and C. eximium, in the springs of 2002 through 2005, when the fruits were ripe. They tasted the fruits of more than 1,500 plants at elevations over a range of 1,000 meters (3,000 feet), mapped the plants' locations, and analyzed their capsaicinoid contents. The populations were generally mixtures of nonpungent and pungent individuals, with the proportion of pungent plants, and the concentration of capsaicinoids in them, increasing at higher elevations.

So high altitude appears to favor spiciness. Why remains unclear. Tewksbury and Levey found that pungent fruits were less likely to show damage from fungal infection, and less likely to be eaten by animals if they had already fallen to the ground. Maybe the microclimate at higher elevation imposes greater physical stress, which makes the fruits more vulnerable to attack by both molds and animals: and capsaicin is an effective chemical defense against both. In any case, we're getting closer to finding out how nature managed to cook up the world's favorite spice.

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Tewksbury, J.J. et al. Where did the chili get its spice? Biogeography of capsaicinoid production in ancestral wild chili species. Journal of Chemical Ecology 2006, 32, 547-64.
http://dx.doi.org/10.1007/s10886-005-9017-4

Chilli pungency: A selective chemical weapon

The paper on chilli archaeology that I described a couple of days ago included two recent references that caught my eye, both by Joshua J. Tewksbury at the University of Washington, Douglas J. Levey of the University of Florida, and various colleagues. They add to our understanding of why it is that chillis evolved to accumulate the chemical, capsaicin, that makes their fruits pungent.

In one of those reports, published in November of last year, Levey, Tewksbury and colleagues tested the theory that capsaicin selectively repels rodents and other grain-eating mammals, which would chew up the chilli's seeds along with the surrounding fruit, while having no deterrent effect on birds, which have no teeth, swallow the fruits whole and defecate the seeds intact. They monitored wild chilli plants in Bolivia and in Arizona with video cameras, and found that only birds ate the fruits, as the theory predicts. Interesting sidelights: in past studies, lab rats frequently fed hot chillis have developed a strong liking for them, just as many humans do. And the wild species that were monitored, Capsicum chacoense and Capsicum annuum, bear fruits with a significant oil content, unlike our domesticated varieties. Oily chillis could be an interesting new ingredient.

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Levey, D.J. et al. A field test of the directed deterrence hypothesis in two species of wild chili. Oecologia 2006, 150: 61-68.
http://dx.doi.org/10.1007/s00442-006-0496-y

Ancient chillis

Spices and herbs are stimulants. Not necessarily pharmacological, but sensory: they stimulate our senses of taste and smell in foods that are otherwise bland. The human diet must have gotten a little boring when our ancestors first learned to cultivate grains and root crops and began to lean heavily on these starchy staffs of life, after millions of years of eating this and that as hunter-gatherers. So when did humans start spicing up their monotonous new diet? Very early--in the Americas, even before the widespread use of cooking pots, according to a new report on the archaeology of the chilli "pepper." A group of fifteen scientists led by Linda Perry of the Smithsonian Museum of Natural History published their results in this week's Science.

Chillis (species of Capsicum) originated in the Americas and are not related to the Asian black and other peppers (species of Piper). Perry and colleagues were able to identify ancient starch granules--"microfossils"-- from domesticated species of Capsicum, by their larger size compared to the starch granules of wild plants. Domesticated starch granules were found in settlements in Central and South America going back as much as 6,000 years. This is as old as the earliest possible date for the oldest known chilli macrofossils, fruits found in the Tehuacan Valley of Mexico. The most ancient sites are in what is now southwestern Ecuador, which is not thought likely to have been a center of chilli domestication, so the spice was probably domesticated elsewhere even earlier and brought there. The starch granules were found on grinding tools and in food remains along with evidence of maize, achira and arrowroot and manioc (starchy rhizome and root vegetables), squashes, jack beans, and palms. The scientists also found domesticated chilli starch in somewhat later sites across a wide region, from central Panama to the Peruvian Andes, Venezuela, and the Bahamas.

Say Perry and colleagues: "The presence of domesticated plants used as condiments rather than as staple foods during the Preceramic period indicates that sophisticated agriculture and complex cuisines arose early throughout the Americas and that the exploitation of maize, root crops, and chili peppers spread before the introduction of pottery."

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Perry, L. et al. Starch fossils and the domestication and dispersal of chili peppers (Capsicum spp. L.) in the Americas. Science 2007, 315, 986-88. http://dx.doi.org/10.1126/science.1136914