Optimal defense theory explains deviations from latitudinal herbivory defense hypothesis
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Kooyers_et_al-2017-Ecology.pdf
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Final Published Version
Affiliation
Univ Arizona, Dept Biol SciIssue Date
2017-04-01Keywords
Mimulus guttatus (common monkeyflower)biogeography
chemical defense
cline
flowering time
genetic constraint
herbivory
latitudinal herbivory defense hypothesis
life history
optimal defense theory
phenylpropanoid glycosides
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WILEYCitation
Kooyers, N. J., Blackman, B. K., & Holeski, L. M. (2017). Optimal defense theory explains deviations from latitudinal herbivory defense hypothesis. Ecology, 98(4), 1036-1048.Journal
ECOLOGYRights
© 2017 by the Ecological Society of America.Collection Information
This item from the UA Faculty Publications collection is made available by the University of Arizona with support from the University of Arizona Libraries. If you have questions, please contact us at repository@u.library.arizona.edu.Abstract
The latitudinal herbivory defense hypothesis (LHDH) postulates that the prevalence of species interactions, including herbivory, is greater at lower latitudes, leading to selection for increased levels of plant defense. While latitudinal defense clines may be caused by spatial variation in herbivore pressure, optimal defense theory predicts that clines could also be caused by ecogeographic variation in the cost of defense. For instance, allocation of resources to defense may not increase plant fitness when growing seasons are short and plants must reproduce quickly. Here we use a common garden experiment to survey genetic variation for constitutive and induced phenylpropanoid glycoside (PPG) concentrations across 35 Mimulus guttatus populations over a similar to 13 degrees latitudinal transect. Our sampling regime is unique among studies of the LHDH in that it allows us to disentangle the effects of growing season length from those of latitude, temperature, and elevation. For five of the seven PPGs surveyed, we find associations between latitude and plant defense that are robust to population structure. However, contrary to the LHDH, only two PPGs were found at higher levels in low latitude populations, and total PPG concentrations were higher at higher latitudes. PPG levels are strongly correlated with growing season length, with higher levels of PPGs in plants from areas with longer growing seasons. Further, flowering time is positively correlated with the concentration of nearly all PPGs, suggesting that there may be a strong trade--off between development time and defense production. Our results reveal that ecogeographic patterns in plant defense may reflect variation in the cost of producing defense compounds in addition to variation in herbivore pressure. Thus, the biogeographic pattern predicted by the LHDH may not be accurate because the underlying factors driving variation in defense, in this case, growing season length, are not always associated with latitude in the same manner. Given these results, we conclude that LHDH cannot be interpreted without considering life history, and we recommend that future work on the LHDH move beyond solely testing the core LHDH prediction and place greater emphasis on isolating agents of selection that generate spatial variation in defense and herbivore pressure.Note
12 month embargo; first published: 10 January 2017.ISSN
0012-9658PubMed ID
28074474DOI
10.1002/ecy.1731Version
Final published versionSponsors
NSF [IOS-1558035]; Northern Arizona University; University of Virginia; University of California, Berkeleyae974a485f413a2113503eed53cd6c53
10.1002/ecy.1731
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