Format: ORAL

Robert S. Boyd

Department of Biological Sciences, Auburn University, Alabama, USA

The unique features of atypical substrates such as ultramafic soils can have important effects on organismal interactions and may provide stimulating avenues for research. Some ultramafic soil plants (metal hyperaccumulators) have extraordinarily elevated metal concentrations (most often nickel). Hyperaccumulated nickel can defend plants against some (unadapted) herbivores and therefore act as an elemental chemical defence. Elemental defences differ from more widely studied organic chemical defences because the toxin is absorbed from the soil (rather than being constructed from photosynthetic products) and an elemental defence cannot be obviated by breaking it down into constituent parts (which is one way that organic defence chemicals can be detoxified by herbivores). But some herbivores (such as the heteropteran Melanotrichus boydi) have apparently evolved metal tolerance and thus can feed with impunity on nickel hyperaccumulators. Elemental defences may even benefit plants that accumulate elements at levels lower than hyperaccumulation thresholds, especially if elemental defences and organic plant defences have additive or synergistic joint effects. This aspect of elemental defences needs further investigation. Plant-herbivore interactions may also influence the color of plant species growing on ultramafic soils. For example, there is a striking correspondence between substrate color and seed coat or leaf colors of some California serpentine plants, suggesting that visual apparency of these plants to herbivores may drive evolution of traits such as seed coat or leaf color. Visual apparency may be an under-studied aspect of plant-herbivore interactions on serpentine and other atypical soils.