Abstract
The deviation from perfect bilateral symmetry is a phenomenon actively exploring in evolutionary and environmental studies. The bilateral variation presents on different ecosystem level. The methods applied vary depending on the task and the final goal of study. The present study demonstrates the statistically significant presence of components (traces) of directional asymmetry (DA), fluctuating asymmetry (FA) and antisymmetry (AS) in leaf blade of Betula pendula on low level of ecosystem such as tree and leaf blade. The Generalized Procrustes Analysis was applied for testing asymmetry of shape in all data set and subgroups. The category ‘population’ revealed no significant value of DA (factor ‘side’). In the levels ‘tree’ and ‘leaf blade’ the factor ‘side’ was statistically significant as well as fluctuating asymmetry (factor interaction ‘leaf × side’).The principal component analysis showed visually the difference in PC scores between antisymmetry matrices of the left and right halves of the leaf blade. Covariate analysis matrices demonstrated the shape deviation from strict symmetry. The metric traits showed directional asymmetry in t-test in the leaf blade and the low kurtosis values. Permutation test of kurtosis values in geometric morphometric approach showed deviation from normality that could verified as a weak presence AS traces. The discriminant analysis results showed that traces of DA differed at the subpopulation level, as three of 10 populations revealed not significant factor ‘side’. Descriptive statistics of the metric train showed a correspondence to the trace of directional asymmetry in the shape of leaf blade. Fluctuating asymmetry in its pure form, at three levels of ecosystem was met only in single population of ten that should be taken into account testing developmental stability of birch and possibly other woody plants.
Highlights
The methods of geometric morphometrics are widely used in ecology for quantifying morphological variation, which can be used for quantifying asymmetry
The purpose of this study was to examine the magnitude of the two kinds of asymmetry (FA and directional asymmetry (DA)) in shape of a Betula pendula Roth leaf in relatively normal ambient conditions at different levels of ecosystem
This article represents the first contribution to the study of asymmetry in subpopulation level in context of relationship between asymmetry in shape and in metric traits
Summary
The methods of geometric morphometrics are widely used in ecology for quantifying morphological variation, which can be used for quantifying asymmetry. The shape of an object is represented by a point in a space of shape variables, which are measurements of a geometric object that are unchanged under similarity transformations. Fluctuating asymmetry (FA) is one of the types of bilateral asymmetry. It is characterized by a slight and statistically insignificant deviation from zero of the difference between the values of the right and the left parts of the homologous bilaterally symmetric trait [1, 2]. FA refers to a certain type of variability – random, or fluctuating [3]. Various bilaterally symmetrical traits have not the same variability in the magnitude of the FA. Ontogenetic development occurs because of an interaction between genetics and the environment and FA could be related to the environment, genetics or both
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