title: A mixed diet of toxic plants enables increased feeding and anti-predator defense by an insect herbivore.
abstract: Some insect herbivores sequester plant secondary metabolites (PSMs) for their own defense, raising the interesting possibility that grazing herbivores are defended by combinations of PSMs from different plant species. In this study, we tested the hypothesis that the grazing caterpillar, Grammia incorrupta, deters the ant, Aphaenogaster cockerelli, by eating a mixture of plants containing iridoid glycosides (IGs) and those containing pyrrolizidine alkaloids (PAs), and that this deterrence is greater than that attained by eating either plant alone. This hypothesis was tested against the non-mutually exclusive hypothesis that mixing plants containing PAs with those containing IGs improves growth performance. Caterpillar survival and growth were measured on three experimental diets: a PA plant, an IG plant, and a mixture of the two. We measured the degree of deterrence associated with these, and an additional experimental diet devoid of PSMs at naturally occurring A. cockerelli nests. Caterpillars fed both plants gained more mass than those fed either plant alone, but took longer to develop. These differences were not caused by diet-based variation in growth efficiency, but by eating more food when offered the mixed-plant diet relative to single-plant diets. The mixed diet was shown to provide deterrence to ants, whereas caterpillars fed single-plant diets were not significantly more deterrent than caterpillars that had eaten the PSM-free diet. We hypothesize that enhanced defense results from increased food consumption in response to multiple plant species, perhaps leading to greater PSM sequestration. Through this mechanism, bottom-up and top-down effects may mutually reinforce the grazing dietary strategy.
authors.affiliation: Department of Ecology and Evolutionary Biology, University of Colorado, Boulder, CO, USA, peri.mason@colorado.edu.
authors.forename: P A
authors.initials: PA
authors.lastname: Mason
authors.forename: M A
authors.initials: MA
authors.lastname: Bernardo
authors.forename: M S
authors.initials: MS
authors.lastname: Singer
mesh_terms: D000818:Animals; D001000:Ants; D004032:Diet; D005247:Feeding Behavior / Q000502:physiology*; D060434:Herbivory; D057889:Iridoid Glycosides / Q000737:chemistry; D007814:Larva / Q000737:chemistry / Q000502:physiology; D009036:Moths / Q000737:chemistry / Q000502:physiology*; D010947:Plants, Toxic / Q000737:chemistry*; D011235:Predatory Behavior; D011763:Pyrrolizidine Alkaloids / Q000737:chemistry
chemical_list: D057889:Iridoid Glycosides; D011763:Pyrrolizidine Alkaloids
references.citation: J Chem Ecol. 2011 Mar;37(3):239-45
references.pmid: 21360275
references.citation: J Chem Ecol. 1989 Jun;15(6):1811-22
references.pmid: 24272184
references.citation: J Chem Ecol. 2006 Jun;32(6):1247-66
references.pmid: 16770716
references.citation: PLoS One. 2010 May 03;5(5):e10435
references.pmid: 20454663
references.citation: Proc Natl Acad Sci U S A. 2004 Dec 28;101(52):18048-52
references.pmid: 15601773
references.citation: Oecologia. 1993 Dec;96(4):575-582
references.pmid: 28312465
references.citation: Science. 1985 Aug 16;229(4714):649-51
references.pmid: 17739376
references.citation: Insect Biochem Mol Biol. 2005 Oct;35(10):1083-99
references.pmid: 16102415
references.citation: J Chem Ecol. 2004 Feb;30(2):229-54
references.pmid: 15112722
references.citation: J Chem Ecol. 2011 Sep;37(9):992-1001
references.pmid: 21858639
references.citation: Annu Rev Entomol. 2009;54:165-87
references.pmid: 18764740
references.citation: J Chem Ecol. 1996 Aug;22(8):1527-39
references.pmid: 24226253
references.citation: Ecology. 2006 Aug;87(8):2103-12
references.pmid: 16937649
references.citation: Mini Rev Med Chem. 2008 Apr;8(4):399-420
references.pmid: 18473930
references.citation: J Exp Biol. 2014 Jul 1;217(Pt 13):2250-60
references.pmid: 24737766
references.citation: Insect Biochem Mol Biol. 2012 Jun;42(6):426-34
references.pmid: 22446106
references.citation: Evolution. 1997 Jun;51(3):873-884
references.pmid: 28568594
references.citation: Oecologia. 1989 May;79(3):427-30
references.pmid: 23921410
references.citation: PLoS One. 2012;7(4):e34403
references.pmid: 22509298
references.citation: J Chem Ecol. 2004 Sep;30(9):1723-41
references.pmid: 15586671
references.citation: Nature. 2005 Jul 28;436(7050):476
references.pmid: 16049466
references.citation: Oecologia. 2001 Sep;129(1):98-105
references.pmid: 28547072
references.citation: Oecologia. 2011 Apr;165(4):995-1005
references.pmid: 20941512
references.citation: PLoS One. 2009;4(3):e4796
references.pmid: 19274098
references.citation: Naturwissenschaften. 2011 Mar;98(3):237-40
references.pmid: 21253684
references.citation: J Insect Physiol. 2001 Sep;47(9):1029-1043
references.pmid: 11472766