Defence syndromes in lodgepole – whitebark pine ecosystems relate to degree of historical exposure to mountain pine beetles. (5th July 2017)

• Record Type: Journal Article
• Authors: Raffa, Kenneth F.; Mason, Charles J.; Bonello, Pierluigi; Cook, Stephen; Erbilgin, Nadir; Keefover‐Ring, Ken; Klutsch, Jennifer G.; Villari, Caterina; Townsend, Philip A.
• Is Part Of: Plant, cell and environment. Volume 40:Number 9(2017)
• Page Start: 1791
• Page End: 1806
• Publication Date: 2017-07-05
• Subjects: Bark beetles -- carbohydrates -- climate change -- conifers -- defence -- fungi -- induction -- ophiostomatoid -- phenolics -- terpenes; Plant physiology -- Periodicals; Plant cells and tissues -- Periodicals; Plant communities -- Periodicals; 581.105
• DOI: 10.1111/pce.12985
• Languages: English
• ISSNs: 0140-7791

Abstract

Abstract : Warming climate is increasing the frequency at which a native tree‐killing insect can survive in ecologically fragile high‐elevation stands dominated by whitebark pine. We analysed a broad range of primary compounds, secondary compounds and minerals, under constitutive and experimentally induced conditions, to compare the defence syndromes of this keystone species with lodgepole pine, the major historical host. Lodgepole pines had higher concentrations of compounds known to be toxic to the mountain pine beetle and its predominant symbiotic fungus, and a chemical composition less conducive to beetles' likelihood of eliciting mass attack, but more conducive to host recognition. During induction, lodgepole pine showed higher concurrence of insecticidal, fungicidal and anti‐aggregant compounds, consistent with a more comprehensively evolved plant defence syndrome. Abstract: Warming climate is allowing tree‐killing bark beetles to expand their ranges and access naïve and semi‐naïve conifers. Conifers respond to attack using complex mixtures of chemical defences that can impede beetle success, but beetles exploit some compounds for host location and communication. Outcomes of changing relationships will depend on concentrations and compositions of multiple host compounds, which are largely unknown. We analysed constitutive and induced chemistries of Dendroctonus ponderosae 's primary historical host, Pinus contorta, and Pinus albicaulis, a high‐elevation species whose encounters with this beetle are transitioning from intermittent to continuous. We quantified multiple classes of terpenes, phenolics, carbohydrates and minerals. Pinus contorta had higher constitutive allocation to, and generally stronger inducibility of, compounds that resist these beetle–fungal complexes. Pinus albicaulis contained higher proportions of specific monoterpenes that enhance pheromone communication, and lower induction of pheromone inhibitors. Induced P. contorta increased insecticidal and fungicidal compounds simultaneously, whereas P. albicaulis responses against these agents were inverse. Induced terpene accumulation was accompanied by decreased non‐structural carbohydrates, primarily sugars, in P. contorta, but not P. albicaulis, which contained primarily starches. These results show some host species with continuous exposure to bark beetles have more thoroughly integrated defence syndromes than less‐continuously exposed host species.