Comparing Variational Properties of Homologous Floral and Vegetative Characters in Dalechampia scandens: Testing the Berg Hypothesis |
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Authors: | Thomas F Hansen Christophe Pélabon W Scott Armbruster |
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Institution: | (1) Department of Biology, Centre for Ecological and Evolutionary Synthesis, University of Oslo, P.O. Box 1050, 0316 Oslo, Norway;(2) Department of Biological Science, Florida State University, Tallahassee, FL 32306, USA;(3) Department of Biology, Population Biology Centre, NTNU, 7491 Trondheim, Norway;(4) Department of Biology, NTNU, 7491 Trondheim, Norway;(5) School of Biological Sciences, King Henry Building University of Portsmouth, Portsmouth, PO1 2DY, UK;(6) Institute of Arctic Biology, University of Alaska, Fairbanks, AK 99775, USA |
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Abstract: | The Berg hypothesis posits that, in plants with specialized pollination systems, floral characters should evolve to become
integrated with each other and decoupled from vegetative characters. We test this hypothesis by comparing serially homologous
and morphologically similar characters in leaves and involucral bracts in the Neotropical vine Dalechampia scandens, which has a specialized pollination system based on resin-collecting bees. The involucral bracts serve a number of specialized
floral functions, including signaling and protection, that may put them under stronger selection for precision than the less
specialized leaves. The homology and morphological similarity of the leaves and bracts allow us to make a sharper test of
Berg’s hypothesis than is possible in most other systems. We found support for the hypothesis in that the bracts had lower
coefficients of variation than the leaves for comparable traits. Also in support of the hypothesis, we found essentially zero
phenotypic correlations between bracts and leaves at the same time that we found moderate correlations between different leaves
and between different bracts. In contradiction to the hypothesis, however, we did not find higher correlations among traits
within bracts than within leaves, and we found no evidence of bracts being more developmentally stable than the leaves. |
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Keywords: | Berg Hypothesis Dalechampia scandens Developmental stability Genetic variance Modularity Phenotypic integration |
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