Eat me, eat me

MOST plants suffer a setback when herbivores nibble their stems and leaves. Not so scarlet gilia, a delicate red-flowered herb found in the mountains of northern Arizona. The herb actually benefits from being eaten, according to Ken Paige of the University of Illinois at Urbana-Champaign. Paige ignited a controversy a decade ago when he reported that gilia that have been nibbled by deer or wapiti produce more seed than those that remain untouched. Many ecologists refused to believe that any species could benefit from being another species’s dinner. Although researchers have since shown similar results in other species, all these studies have dealt exclusively with seed production, overlooking the contribution of pollen. “The important thing is to get genes out, not to worry about whether it’s as Mom or Pop,” says Paige. Now Paige reports that browsing increases gilia’s total reproductive fitness—pollen as well as seed. Gilia plants that Paige had “browsed” by trimming them with scissors regrew to produce over twice as many flowers and pollen grains per plant as uncut plants. Hand pollination experiments showed that the pollen they produced was just as capable of fertilising seeds as that from the uncut plants. Just to be sure, Paige caged five browsed (and regrown) plants and five unbrowsed ones, together with a hummingbird and two hawkmoths, gilia’s natural pollinators. At the end of the growing season, he collected the seeds, sprouted them, and used DNA analysis to determine the paternity of 28 offspring plants. The browsed plants were responsible for 19 of the 28—almost exactly the proportion expected, given their extra pollen count. Gilia’s unusual positive response to browsing suits its circumstances, says Paige. In the mountains of northern Arizona, gilia falls prey to herbivores for a brief but intense period each year, as deer and elk migrate through its mid-elevation habitat on their way to their summer quarters higher up. The plant may have evolved the strategy of sending up a single shoot early in spring as a “deer detector”, he thinks. After this is eaten, the plant can safely send up many more shoots, since the herbivores will by then have moved on. Uneaten plants never get the signal to put out more shoots, so they fail to produce their full quota of flowers,
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