Shrub’s Chemistry Makes Mice Spit Seeds

A desert shrub’s chemical arsenal tricks rodents into spitting out seeds rather than chewing them up, making the animals unwitting accomplices in the plant’s reproduction pathway, researchers report (Curr. Biol., DOI: 10.1016/j.cub.2012.04.051). Many plants use combinations of natural products to ward off predators. But this work, from Michal Samuni-Blank of Israel’s Technion, M. Denise Dearing of the University of Utah, and colleagues, marks the first time researchers have seen chemicals compartmentalized in a way that shapes animal behavior. The shrub, known as taily weed, bears sweet fruit with glucosinolates in its pulp and the enzyme myrosinase in its seeds. If an animal mashes pulp and seeds together at mealtime, the enzyme breaks the glucosinolates down to thiocyanates, isothiocyanates, and nitriles, unleashing an unappetizing, wasabi-like kick of “mustard oil.” With motion-activated cameras, Samuni-Blank watched Cairo spiny mice in the Israeli desert eat taily weed fruit and hock up seeds, presumably to avoid the mustardy sting. The rodents usually spit seeds out in rocky crevices, providing favorable conditions for germination. However, when Samuni-Blank deactivated the plant’s myrosinase in the lab, the mice changed their eating habits, feasting on both fruit and seeds.