The spice is right

For most curry fans, there is nothing like that burning, yet morish, sensation provided by the hot chillies in the recipe, but chilli plants don't exude their spicy flavours for the benefit of humans dining on vindaloo. Their hot tastiness exists to deter herbivores that don't spread the plants seeds, at least according to former University of Montana, Missoula graduate student Josh Tewksbury and ethnobotanist Gary Nabhan of the Arizona Sonora Desert Museum, Tucson.

Tewksbury (now doing post-doc work as a zoologist at the University of Florida, Gainesville) and Nabhan have discovered that the well-known "fiery" molecule capsaicin

	The capsaicin molecule. Click on picture to get molecule in ChemSketch format.

present in the fruit of chilli plants selectively turns off certain would-be diners on chillies. Those that are not good seed dispersers find the chillies distasteful while animals that are good seed scatterers enjoy as much as they like.

The team has found - from trawling through 146 video hours of the comings and goings of animals to chilli plants in the wild - that

Capsicum annuum var. glabrinsculum

cactus mice and packrats are put off by the "heat" of capsaicin from the southern Arizona chilli plant, Capsicum annuum var. glabrinsculum. This, they explains, suits the life cycle of the chilli plant because very few seeds ingested by such small mammals go on to germination once they have been "dropped". On the other hand, the curve-billed thrasher bird (Toxostoma curvorostre) munches through chillies with no such aversion to their taste. This, the team says, is great news for the plant because seeds ingested by these birds thrive. Moreover, the birds tend to deposit seeds in shady sites for future dispersal.

This is the first time that evidence has been found of the ripe fruit of a plant directly deterring those herbivores that would not assist in dispersing its seeds to a good site for new plants to thrive.

Nature, 2001, 412, 403^*

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