Short Communication A Ni hyperaccumulator and a congeneric non-accumulator reveal equally effective defenses against herbivory Liliana Vilas Boas a,b, ⁎ ,1 , Susana C. Gonçalves b,1 , António Portugal b , Helena Freitas b , M. Teresa Gonçalves b a Instituto Superior de Agronomia, Departamento dos Recursos Naturais, Ambiente e Território, Tapada da Ajuda, 1349-017 Lisboa, Portugal b Centre for Functional Ecology, Department of Life Sciences, University of Coimbra, PO Box 3046, 3001-401 Coimbra, Portugal HIGHLIGHTS • The defense hypothesis of Ni hyperaccumulation was tested in Alyssum pintodasilvae. • We compared the effects of A. pintodasilvae and A. simplex on Tribolium castaneum. • No-choice and choice tests were performed using diet disks amended with leaves. • Both high-Ni and low-Ni plants caused significant antifeedant effects on Tribolium. abstract article info Article history: Received 7 December 2012 Received in revised form 26 June 2013 Accepted 27 June 2013 Available online 25 July 2013 Editor: Charlotte Poschenrieder Keywords: Ni hyperaccumulation Alyssum pintodasilvae Alyssum simplex Inorganic defense hypothesis Tribolium castaneum Serpentine soil The defense hypothesis is commonly used to explain the adaptive role of metal hyperaccumulation. We tested this hypothesis using two Brassicaceae congeneric species: Alyssum pintodasilvae, a Ni hyperaccumulator, and the non-accumulator Alyssum simplex both growing on serpentine soils in Portugal. Artificial diet disks amended with powdered leaves from each plant species were used to compare the performance (mortality, biomass change) and feeding behavior of Tribolium castaneum in no-choice and choice tests. The performance of T. castaneum was not affected at several concentrations of A. pintodasilvae or A. simplex in no-choice tests. However, the consumption of plant-amended disks was significantly lower than that of control disks, irrespectively of the species fed. Accordingly, when insects were given an alternative food choice, disks of both plant species were significantly less consumed than control disks. Moreover, insects did not discriminate between disks in the combination “A. pintodasilvae + A. simplex”. Contrary to our expectations, these results suggest that both plant species have equally effective defenses against herbivory. While Ni is believed to be part of the deterrence mechanism in the hyperaccumulator A. pintodasilvae, it seems likely that organic com- pounds, possibly glucosinolates, play an important role in the defense of A. simplex or in both species. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Hyperaccumulator plants take up unusually high amounts of certain inorganic elements (usually metals) from soils and hyperaccumulate them in their shoots (Brooks et al., 1977). Even though metal concentra- tions in shoots range between 100 and 1000 fold higher than usual, plants show no toxicity symptoms. The threshold values defined for hyperaccumulation vary by element: N 10000 μgg -1 for Mn and Zn, N 1000 μgg -1 for As, Co, Cr, Cu, Ni, Se, and Pb, and N 100 μgg -1 for Cd (Ma et al., 2001; Reeves and Baker, 2000). Van der Ent et al. (2013) reported the occurrence of more than 500 hyperaccumulator plant species, the majority of which are Ni hyperaccumulators growing on serpentine soils. Most Ni hyperaccumulators belong to Brassicaceae, Euphorbiaceae and Asteraceae. The genus Alyssum (Brassicaceae) has the biggest number of Ni hyperaccumulators, with more than 50 taxa (Baker and Brooks, 1989; Reeves and Adigüzel, 2004). Several hypotheses have been proposed to explain the adaptive role of metal hyperaccumulation and its functional significance. These include interference with neighboring plant species, metal tolerance/disposal, drought resistance, inadvertent uptake, and defense against natural enemies (Boyd and Martens, 1992, 1998). The “defense hypothesis” (recently renamed “inorganic defense hypothesis” by Boyd (2012) to precise the nature of the chemical defense) has been widely tested for several elements (e.g. Ni, Zn, Cd) and is supported by a growing body of experimental evidence, mostly concerning defense against herbivores (e.g. Behmer et al., 2005; Boyd, 2002; Boyd and Martens, 1994; Boyd and Moar, 1999; Davis and Boyd, 2000; Hanson et al., 2003, 2004; Jhee et al., 1999; Jiang et al., 2005; Martens and Boyd, 1994; Pollard and Baker, 1997), but also against pathogens (Boyd et al., 1994; Fones et al., 2010; Ghaderian et al., 2000). Metal hyperaccumulation Science of the Total Environment 466–467 (2014) 11–15 ⁎ Corresponding author at: Instituto Superior de Agronomia, Departamento dos Recursos Naturais, Ambiente e Território, Tapada da Ajuda, 1349-017 Lisboa, Portugal. E-mail address: liliana.vboas@gmail.com (L. Vilas Boas). 1 Liliana Vilas Boas and Susana C. Gonçalves contributed equally to this work. 0048-9697/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.scitotenv.2013.06.113 Contents lists available at ScienceDirect Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv