Population variation in plant traits associated with ant attraction and herbivory in Chamaecrista fasciculata (Fabaceae) |
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Authors: | Rodrigo S Rios Robert J Marquis John C Flunker |
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Institution: | (1) Department of Biology, University of Missouri-St Louis, One University Boulevard, St Louis, MO 63121-4499, USA;(2) Department of Biology, Saint Louis University, 3507 Laclede Ave., St Louis, MO 63103-2010, USA |
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Abstract: | The benefits of ant–plant–herbivore interactions for the plant depend on the abundance of ants and herbivores and the selective
pressures these arthropods exert. In plants bearing extrafloral nectaries (EFN), different mean trait values may be selected
for by different populations in response to local herbivore pressure, ultimately resulting in the evolution of differences
in plant traits that attract ants as defensive agents against herbivory. To determine if variation in traits that mediate
ant–plant interactions reflect herbivore selective pressures, we quantified intra- and inter-population variation in plant
traits for eight populations of the EFN-bearing annual Chamaecrista fasciculata (Michx.) (Fabaceae). Censuses in rural and urban areas of Missouri and Illinois (USA) showed population differences in ant
attendance and herbivore pressure. Seeds were collected from each population, and plants were grown in a common greenhouse
environment to measure sugar production, nectar volume and composition, EFN size and time of emergence, leaf pubescence, and
leaf quality throughout plant development. Populations varied mainly in terms of nectary size, sugar production, and nectar
volume, but to a lesser degree in leaf pubescence. Populations of C. fasciculata within urban areas (low in insect abundance) had small nectaries and the lowest nectar production. There was a positive correlation
across populations between herbivore density and leaf damage by those herbivores on the one hand and sugar production and
nectar volume on the other. These results, in conjunction with lack of evidence for maternally based environmental effects,
suggest that population differences in herbivore damage have promoted differential evolution of EFN-related traits among populations.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. |
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Keywords: | Ants Chamaecrista fasciculata Extrafloral nectaries Nectar volume Sugar production |
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