Reproducibility of fluctuating asymmetry measurements in plants: Sources of variation and implications for study design |
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| Institution: | 1. Section of Ecology, Department of Biology, University of Turku, 20014 Turku, Finland;2. Laboratory of Insect Ecology, Department of Natural Sciences, Universidade Federal de São João Del-Rei, São João Del-Rei, MG, Brazil;3. Department of Natural Sciences, Pedagogical Institute of Irkutsk State University, Nizhnyaya Naberezhnaya 6, 664011 Irkutsk, Russia;4. Department of Human Physiology and Morphology, Institute of Natural Sciences and Technologies, Northern (Arctic) Federal University, Severodvinskaya 13a, 163002 Arkhangelsk, Russia;5. Section of Biodiversity and Environmental Science, Department of Biology, University of Turku, 20014 Turku, Finland;6. Cleveland State University, 2121 Euclid Ave, Cleveland, OH, 44115 USA;1. Departamento de Botânica, Instituto de Ciências Biológicas e da Saúde, Universidade Federal Rural do Rio de Janeiro – UFRRJ, Seropédica, RJ, 23897-000, Brazil;2. Departamento de Biologia Vegetal, Instituto de Biologia, Universidade Estadual de Campinas – UNICAMP, Campinas, SP, 13083-970, Brazil;3. Instituto de Pesquisas Jardim Botânico do Rio de Janeiro, DIPEQ, Rio de Janeiro, RJ, 22460-030, Brazil;1. State Key Laboratory of Petroleum Resource and Prospecting, College of Geosciences, China Petroleum University, Beijing, 102249, China;2. UNBC, University of North British Columbia, V2N 4Z9, Canada;3. State Key Laboratory of Water Environment Simulation, School of Environment, Beijing Normal University, Beijing, 100875, China;4. Institute for Energy, Environment and Sustainable Communities, University of Regina, 120, 2 Research Drive, Regina, Saskatchewan, S4S 7H9, Canada;5. Beijing Engineering Research Center for Watershed Environmental Restoration & Integrated Ecological Regulation, School of Environment, Beijing Normal University, Beijing 100875, China;6. School of Water Resources & Civil Engineering, China Agriculture University, Beijing 100083, China;1. Department of Statistical Sciences, Sapienza University of Rome, P.le Aldo Moro 5, 00185, Italy;2. Department of Environmental Biology, Sapienza University of Rome, P.le Aldo Moro 5, 00185, Italy;1. Brazilian National Institute for Research in the Amazon, Laboratory of Ecophysiology and Molecular Evolution, Ave André Araújo 2936, 69083-000 Manaus, AM, Brazil;2. Biosciences Institute, São Paulo State University – UNESP, Coastal Campus, Pça Infante Dom Henrique s/n°, P.O. Box 73601, 11380-972, São Vicente, SP, Brazil;3. Department of Environment and Agriculture, Curtin University, P.O. Box U1987, Perth, 6102, Western Australia, Australia;1. Finnish Environment Institute, P.O. Box 111, FI-80101 Joensuu, Finland;2. Department of Geographical and Historical Studies, University of Eastern Finland, 80101 Joensuu, Finland;3. Finnish Environment Institute, P.O. Box 140, FI-00251 Helsinki, Finland;4. Natural Resources Institute Finland, 80101 Joensuu, Finland;1. Universidade Federal de Santa Catarina, Núcleo de Estudos do Mar, 88040-900 Florianópolis, SC, Brazil;2. Universidade Federal de Santa Catarina, Departamento de Bioquímica, 88040-900 Florianópolis, SC, Brazil;3. Universidade Federal de Santa Catarina, Departamento de Química, 88040-900 Florianópolis, SC, Brazil;4. Universidade Federal de Santa Catarina, Departamento de Geociências, Laboratório de Biodiversidade e Conservação Marinha, 88040-900 Florianópolis, SC, Brazil |
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| Abstract: | Fluctuating asymmetry (FA), i.e. small, non-directional deviations from perfect symmetry in morphological characters, increases under genetic and/or environmental stress. Ecological and evolutionary studies addressing FA became popular in past decades; however, their outcomes remain controversial. The discrepancies might be at least partly explained by inconsistent and non-standardised methodology. Our aim was to improve the methodology of these studies by identifying factors that affect the reproducibility of FA measurements in plant leaves. Six observers used a highly standardised measurement protocol to measure FA using the width, area and weight of the same set of leaves of 10 plant species that differed in leaf size, shape of the leaf margin and other leaf traits. On average, 24% of the total variation in the data was due to measurement error. Reproducibility of measurements varied with the shape of leaf margin, leaf size, the measured character and the experience of the observer. The lowest reproducibility of the width of leaf halves was found for simple leaves with serrate margins and the highest for simple leaves with entire margins and for compound pinnate leaves. The reproducibility was significantly lower for the weight of leaf halves than for either their width or area, especially for plants with small leaves. The reproducibility was also lower for measurements made by experienced observers than by naïve observers. The size of press-dried leaves decreased slightly but significantly relative to fresh leaves, but the FA of press-dried leaves adequately reflected the FA of fresh leaves. In contrast, preservation in 60% ethanol did not affect leaf size, but it decreased the width-based values of FA to 89.3% of the values measured from fresh leaves. We suggest that although reproducibility of leaf FA measurements depends upon many factors, the shape of the leaf margin is the most important source of variation. We recommend, whenever possible, choosing large-leaved plants with entire leaf margins as model objects for studies involving measurements of FA using the width of leaf halves. These measurements should be conducted with high accuracy from images of fresh or press-dried leaves. |
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| Keywords: | Accuracy of measurements Measurement error Observer’s experience Sample preservation Selection of study objects Shape of leaf margin |
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