Alkaloid and predation patterns in colorado lupine populations

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Abstract
Colorado populations of herbaceous perennial lupines show three distinct patterns of amounts, kinds, and individual variability of inflorescence alkaloids. These patterns, interpreted as alternative chemical defense strategies, can be related to the susceptibility of populations to attack by larvae of a small flower-feeding lycaenid butterfly, Glaucopsyche lygdamus. In situations ecologically unfavorable to G. lygdumus, lupine populations have “low” alkaloidal profiles, accumulating relatively low amounts of single, bicyclic alkaloids in their inflorescences, with little individual alkaloidal variability, Lupine populations which are quite available to G. lygdamus, on the other hand, accumulate much higher amounts of inflorescence alkaloids. Of these alkaloidally “high” populations, those which suffer only minor predation by G. lygdamus have individually variable mixtures of three or four inflorescence alkaloids, which are found to be isomers of lupanine and closely related tetracyclic compounds. In contrast, those which suffer heavy predation by G. lygdamus show a mixture of nine diverse alkaloidal components including lupanine, hydroxylupanine, and hydroxylupanine esters which is quite invariant from individual to individual. It is hypothesized that individual variability in alkaloids is an anti-specialist chemical defense mechanism. Such individual variability may be advantageous to plant populations by reducing the possibility of selection for strains of specialist herbivores capable of detoxifying or otherwise withstanding plant defensive compounds.