A test of elemental defence against slugs by Ni in hyperaccumulator and non-hyperaccumulator Streptanthus species

Abstract

Tissues of most plant species contain < 10 µg Ni g −1 but Ni hyperaccumulators contain more than 1000 µg Ni g −1 . Hyperaccumulated Ni can defend plants from some herbivores but the defensive role of lesser Ni concentrations is little explored. We raised five species of Streptanthus (Brassicaceae) native to ultramafic soils, one of which (S. polygaloides) is a Ni hyperaccumulator whereas the others are simply Ni-tolerant, on Ni-amended and unamended greenhouse soils to create plants differing in Ni concentrations. On high-Ni soil, leaves of the hyperaccumulator contained 3800 µg Ni g −1 whereas leaves of non-hyperaccumulator species contained 41−64 µg Ni g −1 . Plants of all species grown on low-Ni soils had < 14 µg Ni g −1 . Slugs (Limax maximus) were fed plant material in no-choice tests over a 50-day period and survival and mass changes were recorded. All slugs fed high-Ni leaves of the hyperaccumulator species died within 21 d. Slugs fed high-Ni leaves of the other species did not differ significantly in survival or mass change from those fed low-Ni leaves. In choice tests, slugs (Lehmannia valentiana) offered both high-and low-Ni S. polygaloides leaves did little damage to high-Ni leaves. We conclude that hyperacumulated Ni can defend S. polygaloides from slug herbivory via both toxicity and deterrence, but these defensive effects do not extend to Streptanthus species containing < 70 µg Ni g −1 .

A Ni hyperaccumulator and a congeneric non-accumulator reveal equally effective defenses against herbivory

“…1A-C). Results from the A. pintodasilvae trials provide circumstantial support to the hypothesis that Ni defends this hyperaccumulator species from herbivory in agreement with previous studies on Ni hyperaccumulation Boyd and Jhee, 2005;Boyd and Moar, 1999;Gonçalves et al, 2007;Jhee et al, 2005Jhee et al, , 2006aMartens and Boyd, 1994). However, A. simplex also induced a significant inhibition of food intake and deterred feeding in T. castaneum despite the low concentration of Ni in its leaves (65 ± 26 μg g −1 dry weight).…”

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

“…Feeding deterrence has been demonstrated in Thlaspi caerulescens using both artificial diet and leaves of this hyperaccumulator species (Pollard and Baker 1997;Jhee et al 1999;Behmer et al 2005). Recently, Boyd and Jhee (2005) have shown that Ni can defend the hyperaccumulator Streptanthus polygaloides from slug herbivory via both acute toxicity and deterrence. In another Ni hyperaccumulator, Thlaspi montanum var.…”

“…Furthermore, we do not know how long isopods would have survived if kept under starvation. This kind of control treatment was included by Boyd and Jhee (2005) in their experiments and allowed them to demonstrate an acute toxic effect of high-Ni S. polygaloides since slugs offered these plants had a significantly greater mortality than slugs that were not fed. The much lower amount of A. pintodasilvae litter eaten in comparison with …”

“…In this case, if a choice is provided, high-metal containing material is ingested in lesser extent than lowmetal containing tissue (Jhee et al 1999;Jiang et al 2005). Feeding deterrence is particularly beneficial for plant fitness because it reduces feeding damage (Boyd and Jhee 2005). Nevertheless, though reported, total feeding avoidance is rare (Pollard and Baker 1997).…”

Do metal-rich plants deter herbivores? A field test of the defence hypothesis

“…Recently, high foliar concentrations of heavy metals have also been suggested to act as a defence against herbivores in plants called hyperaccumulators . These plants are able to accumulate heavy metals in their leaves (on a weight/dry weight basis, >0.1% Ni, >1% Zn, >0.01% Cd; Reeves and Baker 2000) up to concentrations that are acutely toxic to several phytophagous invertebrates Boyd and Moar 1999;Boyd et al 2002;Boyd and Jhee 2005).…”