Effects of nickel hyperaccumulation in Alyssum pintodasilvae on model arthropods representatives of two trophic levels

An experimental assessment of the defence hypothesis of nickel ( Ni) hyperaccumulation in Alyssum was lacking. Also, to date no study had investigated the effects of hyperaccumulator litter on a detritivore species. We performed several experiments with model arthropods representatives of two trophic levels: Tribolium castaneum ( herbivore) and Porcellio dilatatus ( detritivore). In no-choice trials using artificial food disks with different Ni concentrations, T. castaneum fed significantly less as Ni concentration increased and totally rejected disks with the highest Ni concentration. In choice tests, insects preferred disks without Ni. In the no-choice experiment, mortality was low and did not differ significantly among treatments. Hence, this suggested a deterrent effect of high Ni diet. Experiments with P. dilatatus showed that isopods fed A. pintodasilvae litter showed significantly greater mortality ( 83%) than isopods fed litter from the non-hyperaccumulator species Iberis procumbens ( 8%), Micromeria juliana ( no mortality) or Alnus glutinosa ( no mortality). Also, isopods consumed significantly greater amounts of litter from the nonhyperaccumulator plant species. The behaviour of isopods fed A. pintodasilvae litter suggested an antifeedant effect of Ni, possibly due to postingestive toxic effects. Our results support the view that Ni defends the Portuguese serpentine hyperaccumulator A. pintodasilvae against herbivores, indicating that Ni can account both for feeding deterrence and toxic effects. The effects of hyperaccumulator litter on the detritivore P. dilatatus suggest that the activity of these important organisms may be significantly impaired with potential consequences on the decomposition processes.