Fluctuating asymmetry (FA) is a non-specific stress indicator and describe developmental instability in bilateral
structure. In plants, FA has been used as a tool for monitoring levels of ecological stress, however, in trees, high value of leaf FA has been assumed to indicate the level of environmental stresses. In this work, I analyzed the FA response to abiotic stress in the Betula pendula Roth leaves in two contrasting sites (polluted vs unpolluted). I also investigated whether another biometrical leaf feature is able to determine FA as an environmental stress indicator. After the cluster analysis and mixed-model ANOVA, I selected one feature, which was leaf apical angle. Results showed significant differences (using chi square test) in apical angle FA in the unpolluted site as compared to the polluted one. Concluding, I suggested that plants living in more
stressful sites are more symmetrical and leaf FA for plant species with a wide ecological distribution such as Betula pendula should be used as an index of environmental quality

Franiel, Izabella

Biodiversity Research and Conservation

English

Repozytorium Uniwersytetu Śląskiego RE-BUŚ

             Title: Fluctuating asymmetry of Betula pendula Roth leaves - an index of environment quality  Author: Izabella Franiel  Citation style: Franiel Izabella. (2008). Fluctuating asymmetry of Betula pendula Roth leaves - an index of environment quality. "Biodiversity Research and Conservation" (Vol.9/10, (2008), s. 7-10).  © Adam Mickiewicz University in PoznaÒ (Poland), Department of Plant Taxonomy. All rights reserved. BRCwww.brc.amu.edu.plFluctuating asymmetry of Betula pendula Roth leavesñ an index of environment qualityIzabella FranielDepartment of Ecology, University of Silesia, Bankowa 9, 40-007 Katowice, Poland, e-mail: izabella.franiel@us.edu.plAbstract: Fluctuating asymmetry (FA) is a non-specific stress indicator and describe developmental instability in bilateralstructure. In plants, FA has been used as a tool for monitoring levels of ecological stress, however, in trees, high value of leafFA has been assumed to indicate the level of environmental stresses. In this work, I analyzed the FA response to abiotic stressin the Betula pendula Roth leaves in two contrasting sites (polluted vs unpolluted). I also investigated whether another bio-metrical leaf feature is able to determine FA as an environmental stress indicator. After the cluster analysis and mixed-modelANOVA, I selected one feature, which was leaf apical angle. Results showed significant differences (using chi square test) inapical angle FA in the unpolluted site as compared to the polluted one. Concluding, I suggested that plants living in morestressful sites are more symmetrical and leaf FA for plant species with a wide ecological distribution such as Betula pendulashould be used as an index of environmental quality.Key words: fluctuating asymmetry, environmental stress, Betula pendula, cluster analysis1. IntroductionFluctuating asymmetry (FA) is one of the stress indicesused recently to assess a subtle effect of environmentaldegradation on organisms and is expected to increaseunder stress condition. Developmental stability can bedefined as a capacity of an individual to correct randomdisturbances caused by developmental noise. Increaseddevelopmental stability results in higher developmentalprecision and decreased FA factor. Developmentalinstability is a series of processes that tend to disruptprecise development (Palmer & Strobeck 2003). Moresymmetric individuals have greater developmental sta-bility and usually achieve greater reproductive successand better survival rates than asymmetric individuals(Freeman et al. 1993). Measures of developmental in-stability, such as FA, may provide more sensitive indi-cator of stress than traditional methods (Rettig et al.1997). FA changes in plants can be sometimes hardlynoticeable (changes of about 1% in the value of theobserved feature), but some of them are quite apparent.Abiotic environmental stress can also cause the increaseof FA in plants. Such an increase was observed asa result of increase in 137Cs radiation levels in treespecies like Robinia pseudacacia, Sorbus aucuparia andMatricaria perforata (M¸ller 1998). Kozlov et al.(1996) demonstrated a positive correlation between FAof birch leaves (Betula pubescens and Betula pendula)and metal and chemical pollution.The present study was carried out on heavily pol-luted site (slag industrial waste dump) and relativelyclean site (control site), both located in the Upper Silesiaregion. The neutral pH of the waste material and highconcentrations of heavy metals (Zn 100-1078 mg/kgdry weight of soil; Pb 196,9-1331 mg/kg dry weight ofsoil, Cd 1-9 mg/kg dry weight of soil) were of greatinterest, especially compared with total zinc concentra-tion in soil under cultivation 15 to 300 mg/kg dry weightof soil, total lead 80-200 mg/kg dry weight of soil andcadmium ca. 1 mg/kg dry weight of soil (Franiel &WiÍski 2005).In this study, I try to distinguish which of biometri-cal leaves features of Betula pendula, besides width andsurface, is the most useful to determine fluctuatingasymmetry as an environmental stress indicator. More-over, I try to determine if leaf FA features should beconsidered as an environmental indicator of habitatquality.Biodiv. Res. Conserv. 9-10: 7-10, 2008VARIABILITY, TAXONOMY AND PHYLOGENY82. Material and methodsFor the present research 100 birch leaves, i.e. thesecond leaf from the current-year short sterile shoots inthe middle of the crown of each individual, were collected.Only healthy, whole and fully developed leaves weresampled and collected during one week at the end ofJune 2005 year (at least 40 birch trees were selectedand 8.000 leaves were collected). The leaves werepressed in a herbarium press and identified individually.After drying, each leaf was scanned and its five featureswere measured with ANALYSIS 5.1 software (Olym-pus, Japan): F1 ñ left and right apical angle, F2 ñ leftand right basal angle, F3 ñ left and right angle betweensecond vein and midrib, F4 ñ left and right distancemeasured from the sixth and seventh veins, F5 ñ leftand right number of teeth between the sixth and seventhveins.  In order to determine which leaf features vari-ables discriminated between both (polluted and unpol-luted) birch populations, a cluster analysis was used.Three kinds of bilateral asymmetry (antisymmetry,directional asymmetry ñ DA and fluctuating asymmetryñ FA) were distinguished by statistical methods.Because FA is subjected to measurement error, all leaveswere measured three times to minimize the influenceof measurement error in the analysis (Palmer & Strobeck1986). To check for antisymmetry ñ significant differen-ces in the R-L distribution comparing to the normalcurve, Shapiro-Wilk test was used (p>0.05). A mixed-modelANOVA was used for each feature to find out the degreeof directional asymmetry and fluctuating asymmetry.Significant difference between leaf side and individualdata of trees indicate presence of fluctuating asymmetry,however, significant differences between the left andright side of analyzed feature indicate directional asym-metry. Directional symmetry appears if larger valuesconsistently occur on one side. If data sets demonstratedthat fluctuating asymmetry exist, FA value was estimatedusing protocol recommended by Palmer & Strobeck(1986). Absolute FA ([R-L]/size, where size=[R+L]/2)was calculated for the selected leaf feature. Dividing[R-L] by size accounts for variation in trait size.In addition, to check significant differences betweenhabitats for previously selected FA feature, a chi squaretest was used. The factor considered in the statisticalanalyses were the study sites (the two sampling locali-ties: polluted and unpolluted) and individual birch trees;the variable was (log x+1) transformed FA apical angle.All analyses were performed with Statistica 7.0 PL(StatSoft, Poland) software.3. ResultsIn order to determine which leaf features (F1-F5)variables discriminated between zinc dump and controlarea populations a cluster analysis was used. Results ofcluster analysis allowed me to make a clear distinctionbetween apical angle (F1) and the rest of leaf features(Fig. 1). Leaf deviation from symmetry showed a statisticalnormal distribution as evaluated by the Shapiro-WilkIzabella Franiel Fluctuating Asymmetry of Betula pendula Roth leaves ñ an index of environment...Fig. 1. Cluster analysis on measured features of leaves collected from 40 trees in the polluted and control habitats. Dendrogram based onEuclidean distance, using the Ward methodExplanations: F1 ñ left and right apical angle, F2 ñ left and right basal angle, F3 ñ left and right angle between second vein and midrib, F4 ñ left and rightdistance measured from the leaf sixth and seventh veins, F5 ñ left and right number of teeth between the sixth and seventh veins	9test (α = 0.05), thus suggesting the absence of anti-symmetry for all features in polluted and unpolluted sites.The slight initial preference is ultimately amplified intoa large consistent difference. I confirmed this result byt-test for independent samples (p<0.01), showing sig-nificant differences between left and right side. Afterthe mixed-model ANOVA test, one feature, which wasapical angle, was selected. Then, only for this featurePalmerís & Strobeckís (1986) protocol was used to assesenvironmental quality for both habitats (Table 1). Re-sults showed a significant differences (using chi squaretest: chi square=91.65, p=0.000, df=1) in apical angleFA in the unpolluted site as compared to the pollutedone.4. DiscussionGenetic and environmental stress influences develop-mental stability, causing phenotypic traits to fluctuateabove the level of natural variation. One way to measurethe magnitude of environmental stress is the measure-ment of resident organism response to abiotic and bioticstress. Abiotic stress factors such as water limitation,as well as temperature, nutrition, pollutants and bioticstress factors, such as population density, can signifi-cantly affect FA indices. However, my results showedthat trees growing on unfavorable sites are more symme-trical. Drought and concentration of heavy metals werea major factor determining angle FA in Betula pendula.There was significant increase in apical angle FA in theunpolluted site as compared to the polluted one. Ambo-Rappe et al. (2008), who study FA in plants growing incontaminated sites, suggested that there is a possibilitythat heavy metal exposure induced or activated someenzymes, such as phytochelatin synthase, that protec-tplant development from further damage. Plants frompolluted sites perform better against stressful situationbecause they are adopted to those condition and are moresymmetrical (HÛdar 2002). Another possible reason forthe decline of FA value in the polluted site may be aneffect of natural selection leading to adaptation to lifein those locations (Ambo-Rappe et al. 2008). A note-worthy possibility has been suggested by Hochwender& Fritz (1999), who found increased leaf FA in willowtrees growing in optimal biotic conditions, suggestedthat it can be caused by very fast leaf growth which candisturb development processes.A good ecological indicator must be sensitive enoughto provide early warning signals. Since FA reveals smallchanges in tree development processes, it may besensitive enough to show stress levels that are nothigh enough to affect the measures of fitness, such asgrowth and reproduction. Looking for a good indicator,we need to determine the level of stress in an ecosystembefore it affects the critical Ñred lineî of its residentorganisms.The investigation has showed that apical angle maybe used as a good feature, beside width and surface, forevaluation of FA factor. Most contaminated sites (e.g.zinc dump) are generally not polluted by only onechemical substance but by a mixture of pollutants, whichmay lead to many synergistic effects. It is thus importantto develop a sensitive bioassay that can monitor overallstress. If we can account for the effect of abiotic (weatherconditions and pollution) stress on FA, we can use FAindices as a holistic bioassay tool for overall eco-system level, besides the individual effects (Mal et al.2002).Biodiv. Res. Conserv. 9-10: 7-10, 2008Table 1. Results of tests for significance of FA for the leaf left and right apical angle (trait F1) in the zinc dump (polluted) andcontrol area (unpolluted) populationsExplanation: * ñ indicates significant difference at p<0.05Mixed-model ANOVA for Trait Study plot Number of leaves collected side individ. side x individ. (R-L) Index of FA Antisymmetry W polluted 4000 0.188   0.000* 0.011* 0.461 0.119   0.992* Apical angle unpolluted 4000 0.151 0.168 0.000* 0.481 0.124 0.984 ReferencesAMBO-RAPPE R., LAJUS D. L. & SCHREIDER M. J. 2008. In-creased heavy metal and nutrient contamination doesnot increase fluctuating asymmetry in the seagrassHalophila ovalis. Ecol. Indicat 8: 100-103.FRANIEL I. & WI SKI K. 2005. Leaf features of silver birch(Betula pendula Roth). Variability within and betweentwo populations (uncontaminated vs Pb-contaminatedand Zn-contaminated site). Trees 19: 81-88.10FREEMAN D. C., GRAHAM J. H. & EMLEN J. M. 1993. Develop-mental stability in plants: symmetries, stress andepigenesist. Genetica 89: 97-119.HOCHWENDER C. G. & FRITZ R. S. 1999. Fluctuating asymme-try in Salix hybrid systems: the importance of geneticversus environmental causes. Evolution 53: 408-416.H”DAR J. A. 2002. Leaf fluctuating asymmetry of Holm oakin response to drought under contrasting climatic con-ditions. J. Arid Environ. 52: 233-243.KOZLOV M. V., WILSEY B. J., KORICHEVA J. & HAUKIOJA E.1996. Fluctuating asymmetry of birch leaves increasesunder pollution impact. J. Appl. Ecol. 33: 1489-1495.MAL T. K., UVEGES K. & TURK W. 2002. Fluctuating asym-metry as an ecological indicator of heavy metal stressin Lythrum salicaria. Ecol. Indicat. 1: 189-195.M‹LLER A. P. 1998. Developmental instability of plantsand radiation from Chernobyl. Oikos 81(3): 444-448.PALMER A. R. & STROBECK C. 1986. Fluctuating asymmetry.Measurement, Analysis, Patterns. Ann. Rev. Ecol.Sys. 17: 391-421.PALMER A. R. & STROBECK C. 2003. Fluctuating AsymmetryAnalyses Revisited. In: M. POLAK (ed.). Develop-mental Instability (DI). Causes and Consequences, pp.279-319. Oxford University Press, London.RETTIG J. E., FULLER R. C., CORBETT A. L. & GETTY T. 1997.Fluctuating asymmetry indicates levels of competi-tion in an even-aged poplar clone. Oikos 80(1): 123-127.Izabella Franiel Fluctuating Asymmetry of Betula pendula Roth leaves ñ an index of environment...

Fluctuating asymmetry of Betula pendula Roth leaves - an index of environment quality

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Fluctuating asymmetry of Betula pendula Roth leaves - an index of environment quality

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