Higher Allocation to Low Cost Chemical Defenses in Invasive Species of Hawaii

Abstract

The capacity to produce carbon-based secondary compounds (CBSC), such as phenolics (including tannins) and terpenes as defensive compounds against herbivores or against neighboring competing plants can be involved in the competition between alien and native plant species. Since the Hawaiian Islands are especially vulnerable to invasions by alien species, we compared total phenolic (TP), total tannin (Tta), and total terpene (TT) leaf contents of alien and native plants on Oahu Island (Hawaii). We analyzed 35 native and 38 alien woody plant species randomly chosen among representative current Hawaiian flora. None of these CBSC exhibited phylogenetic fingerprinting. Alien species had similar leaf TP and leaf Tta contents, and 135% higher leaf TT contents compared with native species. Alien plants had 80% higher leaf TT:N leaf content ratio than native plants. The results suggest that apart from greater growth rate and greater nutrient use, alien success in Oahu also may be linked to greater contents of low cost chemical defenses, such as terpenes, as expected in faster-growing species in resource rich regions. The higher TT contents in aliens may counterbalance their lower investment in leaf structural defenses and their higher leaf nutritional quality. The higher TT provides higher effectiveness in deterring the generalist herbivores of the introduced range, where specialist herbivores are absent. In addition, higher TT contents may favor aliens conferring higher protection against abiotic and biotic stressors. The higher terpene accumulation was independent of the alien species origin, which indicates that being alien either selects for higher terpene contents post-invasion, or that species with high terpene contents are pre-adapted to invasiveness. Although less likely, an originally lower terpene accumulation in Hawaiian than in continental plants that avoids the increased attraction of specialist enemies associated to terpenes may not be discarded.

Field Spectroscopy in the VNIR-SWIR Region to Discriminate between Mediterranean Native Plants and Exotic-Invasive Shrubs Based on Leaf Tannin Content

“…We assume that with the absence of specialist herbivores or pathogens in the Portuguese coastal dunes, A. longifolia is able to change the resource allocation from defense to increased growth or reproduction. This reduced secondary plant metabolism (in particular, with respect to tannins) of invasive plant species introduced into a new range was also reported by the studies of Peñuelas et al [46], Wang et al [47] and Omelchuk et al [48]. This would support the evolution of increased competitive ability (EICA) hypothesis by Blossey and Nötzold [49], which states that invasive species can alter their metabolism, so that the competitive ability is increased and the amount of resources needed for defense is reduced in absence of enemies.…”

Lower P contents and more widespread terpene presence in old Bornean than in young Hawaiian tropical plant species guilds

“…The improvement relative to standard assay was the use of a blank of polyvinylpolypyrrolidone (PVPP). PVPP retains the phenolic compounds avoiding their reaction with Folin-Ciocalteu solution, thereby providing a true blank sample (see Peñuelas et al 2010b). The absorbances of the samples were determined at 760 nm using a spectrophotometer Helios Alpha (Thermo Spectronic, Cambridge, UK).…”

Foliar chemistry and standing folivory of early and late-successional species in a Bornean rainforest

“…Phenolics and tannins are secondary metabolites that act as defensive compounds (Reed 1995). Phenolics are present in high concentrations in leaf tissues (typically between 5-40% dry weight) (Meyer and Karasov 1989;Adams et al 2009;Peñuelas, Sardans, Llusia, Owen, Silva A c c e p t e d M a n u s c r i p t et al 2010). They are effective against a broad range of herbivores (Coley et al 1985;Kouki and Manetas 2002;Novotny et al 2002).…”