title: Is protection against florivory consistent with the optimal defense hypothesis?
abstract: BACKGROUND
  Plant defense traits require resources and energy that plants may otherwise use for growth and reproduction. In order to most efficiently protect plant tissues from herbivory, one widely accepted assumption of the optimal defense hypothesis states that plants protect tissues most relevant to fitness. Reproductive organs directly determining plant fitness, including flowers and immature fruit, as well as young, productive leaf tissue thus should be particularly well-defended. To test this hypothesis, we quantified the cyanogenic potential (HCNp)-a direct, chemical defense-systemically expressed in vegetative and reproductive organs in lima bean (Phaseolus lunatus), and we tested susceptibility of these organs in bioassays with a generalist insect herbivore, the Large Yellow Underwing (Noctuidae: Noctua pronuba). To determine the actual impact of either florivory (herbivory on flowers) or folivory on seed production as a measure of maternal fitness, we removed varying percentages of total flowers or young leaf tissue and quantified developing fruit, seeds, and seed viability.
  
  
  RESULTS
  We found extremely low HCNp in flowers (8.66 ± 2.19 μmol CN(-) g(-1) FW in young, white flowers, 6.23 ± 1.25 μmol CN(-) g(-1) FW in mature, yellow flowers) and in pods (ranging from 32.05 ± 7.08 to 0.09 ± 0.08 μmol CN(-) g(-1) FW in young to mature pods, respectively) whereas young leaves showed high levels of defense (67.35 ± 3.15 μmol CN(-) g(-1) FW). Correspondingly, herbivores consumed more flowers than any other tissue, which, when taken alone, appears to contradict the optimal defense hypothesis. However, experimentally removing flowers did not significantly impact fitness, while leaf tissue removal significantly reduced production of viable seeds.
  
  
  CONCLUSIONS
  Even though flowers were the least defended and most consumed, our results support the optimal defense hypothesis due to i) the lack of flower removal effects on fitness and ii) the high defense investment in young leaves, which have high consequences for fitness. These data highlight the importance of considering plant defense interactions from multiple angles; interpreting where empirical data fit within any plant defense hypothesis requires understanding the fitness consequences associated with the observed defense pattern.
authors.affiliation: Department of Biology, Portland State University, 1719 SW 10th Ave, Portland, OR, 97201, USA. adrg@pdx.edu.
authors.forename: Adrienne L
authors.initials: AL
authors.lastname: Godschalx
authors.affiliation: Department of Biology, Portland State University, 1719 SW 10th Ave, Portland, OR, 97201, USA. stady@pdx.edu.
authors.forename: Lauren
authors.initials: L
authors.lastname: Stady
authors.affiliation: Department of Biology, Portland State University, 1719 SW 10th Ave, Portland, OR, 97201, USA. bwatzig@pdx.edu.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Watzig
authors.affiliation: Department of Biology, Portland State University, 1719 SW 10th Ave, Portland, OR, 97201, USA. ballhorn@pdx.edu.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Ballhorn
mesh_terms: D000818:Animals; D003486:Cyanides / Q000378:metabolism; D004734:Energy Metabolism; D035264:Flowers / Q000469:parasitology*; D005960:Glucosides / Q000378:metabolism; D060434:Herbivory; D009036:Moths / Q000502:physiology*; D027805:Phaseolus / Q000276:immunology / Q000469:parasitology*; D018515:Plant Leaves / Q000469:parasitology; D012098:Reproduction; D012639:Seeds / Q000469:parasitology
chemical_list: D003486:Cyanides; D005960:Glucosides
references.citation: Toxicon. 2000 Jan;38(1):11-36
references.pmid: 10669009
references.citation: Phytochemistry. 2003 Feb;62(3):471-81
references.pmid: 12620360
references.citation: Tree Physiol. 2000 May;20(9):591-598
references.pmid: 12651423
references.citation: Q Rev Biol. 2003 Mar;78(1):23-55
references.pmid: 12661508
references.citation: J Biol Chem. 1964 Jun;239:1674-9
references.pmid: 14213333
references.citation: Tree Physiol. 2004 Jun;24(6):681-8
references.pmid: 15059768
references.citation: Oecologia. 2005 Dec;146(2):169-78
references.pmid: 16096848
references.citation: J Chem Ecol. 2005 Jul;31(7):1445-73
references.pmid: 16222786
references.citation: J Chem Ecol. 2006 Feb;32(2):261-75
references.pmid: 16541336
references.citation: Plant Physiol. 1986 Dec;82(4):946-51
references.pmid: 16665171
references.citation: Plant Physiol. 1987 Aug;84(4):1296-300
references.pmid: 16665601
references.citation: Plant Physiol. 1989 May;90(1):33-6
references.pmid: 16666758
references.citation: Plant Physiol. 1990 Oct;94(2):401-5
references.pmid: 16667728
references.citation: Ecology. 2006 Jul;87(7 Suppl):S132-49
references.pmid: 16922309
references.citation: Ecol Lett. 2006 Dec;9(12):1351-65
references.pmid: 17118009
references.citation: J Chem Ecol. 2007 Dec;33(12):2195-208
references.pmid: 17987336
references.citation: Planta. 2008 Aug;228(3):449-57
references.pmid: 18493790
references.citation: J Chem Ecol. 2008 Oct;34(10):1298-301
references.pmid: 18758862
references.citation: Plant Biol (Stuttg). 2009 Jan;11(1):38-45
references.pmid: 19121112
references.citation: Am J Primatol. 2009 Apr;71(4):305-15
references.pmid: 19132732
references.citation: Tree Physiol. 2010 Sep;30(9):1111-7
references.pmid: 20573780
references.citation: J Chem Ecol. 2011 Feb;37(2):141-4
references.pmid: 21221741
references.citation: Am J Bot. 2010 Apr;97(4):601-10
references.pmid: 21622422
references.citation: Ecology. 2012 Aug;93(8):1912-21
references.pmid: 22928419
references.citation: New Phytol. 2013 Jan;197(2):359-61
references.pmid: 23253329
references.citation: J Exp Bot. 2013 Mar;64(5):1317-32
references.pmid: 23404899
references.citation: PLoS One. 2013;8(2):e55602
references.pmid: 23405176
references.citation: J Chem Ecol. 2013 Mar;39(3):413-7
references.pmid: 23417653
references.citation: J Chem Ecol. 2014 Mar;40(3):294-6
references.pmid: 24573494
references.citation: Annu Rev Plant Biol. 2014;65:155-85
references.pmid: 24579992
references.citation: New Phytol. 2014 Jun;202(4):1357-70
references.pmid: 24611577
references.citation: New Phytol. 2014 Jul;203(2):607-19
references.pmid: 24739022
references.citation: Oecologia. 2014 Nov;176(3):811-24
references.pmid: 25173086
references.citation: Ecology. 2015 Feb;96(2):348-54
references.pmid: 26240856
references.citation: Oecologia. 1992 Oct;91(4):540-547
references.pmid: 28313508
references.citation: Evolution. 1989 Jul;43(4):870-881
references.pmid: 28564205
references.citation: J Biol Chem. 1970 Mar 10;245(5):917-22
references.pmid: 5417265
references.citation: Anal Biochem. 1976 May 7;72:248-54
references.pmid: 942051
references.citation: Proc Natl Acad Sci U S A. 1998 Apr 14;95(8):4410-4
references.pmid: 9539750