Nickel defends the South African hyperaccumulator Senecio coronatus (Asteraceae) against Helix aspersa (Mollusca: Pulmonidae)

Abstract

The elevated Ni concentration of Ni hyperaccumulator plants has been proposed to be an effective chemical defence against herbivores. To test this hypothesis, we fed leaves from hyperaccumulator and non-hyperaccumulator populations of South African Senecio coronatus to a generalist herbivore species, the brown garden snail (Helix aspersa). Snails fed hyperaccumulator leaves experienced significantly greater mortality than those fed non-hyperaccumulator leaves and also contained 10-fold greater concentrations of Ni. A choice experiment showed snails preferred non-hyperaccumulator leaves in two of three trials. Snails fed cornmeal diet amended with Ni had significantly reduced mass for diets containing as little as 140 μg Ni g-1, and significantly greater mortality occurred for snails consuming diets containing 830 μg Ni g-1 and greater. Because hyperaccumulator S. coronatus leaves contained far more Ni (12,100 μg Ni g-1) than the toxic threshold shown in the diet experiment, we concluded that the Ni concentration of hyperaccumulator leaves was sufficient to cause the elevated mortality of snails fed those leaves. This research adds another example to the growing literature showing the toxicity of hyperaccumulated Ni to generalist folivores.