The increase of fluctuating asymmetry in a monoclonal strain of collembolans after chemical exposure - discussing a new method for estimating the environmental variance
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The increasing demand for detecting and quantifying the negative effects on natural habitats caused by anthropogenic activity has led to the development of impact assessment tools. Here, we propose a monitoring method based on the concept of developmental instability (DI) estimated from fluctuating asymmetry (FA) in bilateral morphological traits in a monoclonal strain. The use of monoclonal populations conveys certain advantages over sexual populations when interpreting fluctuating asymmetry results. This is because the inherent problems of genetic heterogeneity are circumvented. Our investigation demonstrates in practice, how an estimate of the environmental component of the phenotypic variance in a population can be achieved. This estimate can be used to eliminate samples where the presence of macro environmental variance has influenced the estimated level of fluctuating asymmetry significantly. Avoiding the confounding effect due to the presence of genetic variance and controlling the environmental variance component enable a more accurate estimate of the possible detrimental effects of the putative stressing agents. We used a clonal strain of the springtail Folsomia candida exposed to three different contaminants; tributyltin, nonylphenol and bis(2-ethylhexyl)-phthalate (DEPH), in order to test the general applicability of the proposed method. The results show that the method is efficient in discriminating between environments exposed to chemical stress and control environments. However, establishing an actual dose-response relationship was only possible for one of the contaminants, nonylphenol.