Chenopod salt bladders deter insect herbivores
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Trichomes on leaves and stems of certain chenopods (Chenopodiaceae) are modified with a greatly enlarged apical cell (a salt bladder), containing a huge central vacuole. These structures may aid in the extreme salt tolerance of many species by concentrating salts in the vacuole. Bladders eventually burst, covering the leaf in residue of bladder membranes and solid precipitates. The presence of this system in non-halophytic species suggests additional functions. I tested the novel hypothesis that these bladders have a defensive function against insect herbivores using choice, no choice, and field tests. Generalist insect herbivores preferred to feed on leaves without salt bladders in choice tests. In no choice tests, herbivores consumed less leaf matter with bladders. In a field test, leaves from which I had removed bladders suffered greater herbivory than adjacent leaves with bladders. Solutions containing bladders added to otherwise preferred leaves deterred herbivores, suggesting a water-soluble chemical component to the defense. This bladder system has a defensive function in at least four genera of chenopods. Salt bladders may be a structural defense, like spines or domatia, but also have a chemical defense component.
KeywordsPlant–herbivore interaction Salt bladders Salt hairs Vesicular hairs Chenopodiaceae Chenopodium Atriplex
R. Karban, L. Yang (and lab group), J. Rosenheim, J. Richards, J. Piova-Scott, D. Morse, J. Blyth, J. Clegg, K. Hughes, and K. Mac Millen provided insightful conversations and commentary on the project and manuscript. Z. Chapman fastidiously edited the manuscript. R. Brennan, G. Charles, D. Klittich, W. Krimmel, and C. Nerkhorn provided field assistance. K. Ullman supplied innumerable beetles. The USDA GRIN program and K. Mac Millen provided seeds and seedlings; D. Brenner and K. Wells of the USDA provided helpful propagation advice. J. Shepard provided herbarium assistance. C. Koehler and P. Aigner facilitated work at McLaughlin Reserve. C. Eisemann and S. Clark determined the Monoxia. E. LoPresti was supported by an ecology graduate group fellowship at UC Davis and received funding for this study from the Center for Population Biology and the Jastro-Shields fund.
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