Fluctuating asymmetry of plants

Past research

Symmetry pervades nature, but asymmetry is rather common as well. If we perceive symmetry positively, as a sign of beauty or perfection, does this mean that asymmetry is a sign of ugliness or imperfection? An answer in the positive predominated during the past decades, when the search for correlations between stress and fluctuating asymmetry (FA; small deviations from perfect bilateral symmetry) became increasingly popular. My team began to explore the FA of plants in the early 1990s, originally in connection with studies of the pollution impact on terrestrial ecosystems. We developed a methodology for assessment of FA in conifers, documented leaf/needle FA of woody plants along multiple pollution gradients, analysed the induction of FA by herbivory, explored the climatic impact on plant FA and discussed the relationships between plant performance and FA. During the 2000s, emphasis was placed on using FA for testing the predictions of general ecological theories.

Ongoing research

We are now investigating factors that affect the reproducibility of FA measurements in plant leaves, continuing our monitoring of leaf FA in birches growing along strong pollution gradients (ongoing since 1993) and exploring the effects of within-plant variation in FA on plant-feeding insects.

Featured publications

Kozlov, M. V., Wilsey, B. J., Koricheva, J. & Haukioja, E. (1996) Fluctuating asymmetry of birch leaves increases under pollution impact. Journal of Applied Ecology33, 1489-1495 (doi: 10.2307/2404787)».

Fluctuating asymmetry (FA) of birch leaves decreased hyperbolically with distance from four sources of aerial emission in NW Europe which differed in amounts and composition of pollutants. The extent of the zone of increased FA was higher around polluters which produced more emissions. FA of leaves sampled around two copper-nickel smelters was positively related to foliar nickel concentrations, and regressions from these two sites had similar slopes and intercepts. Thus, FA of birch leaves may represent a convenient indicator for rapid assessment of environmental quality.

Kozlov, M. V. & Zvereva, E. L. (2015) Confirmation bias in studies of fluctuating asymmetry. Ecological Indicators57, 293-297 (doi: 10.1016/j.ecoind.2015.05.014).

We experimentally tested the hypothesis that the outcomes of studies addressing fluctuating asymmetry may be influenced by confirmation bias, i.e. the tendency of humans to seek out evidence in a manner that confirms their hypotheses and beliefs. We asked each of 31 scientists to measure FA from the scanned images of the same set of birch leaves and provided these scientists with either true or false information about the origin of these leaves. The participants who believed that the leaves originated from a heavily polluted site reported significantly higher values of FA when compared to the participants who believed that the leaves were collected from an unpolluted site. We conclude that when scientists expected to find high FA in some samples, the results of their measurements confirmed their expectations.

Kozlov, M. V. (2015) How reproducible are the measurements of leaf fluctuating asymmetry? PeerJ3,  e1027 (doi: 10.7717/peerj.1027).

The reproducibility of fluctuating asymmetry (FA) was explored by comparing the results of measurements of scanned images of 100 leaves of downy birch conducted by 31 volunteer scientists experienced in studying plant FA. The overall reproducibility of the results among the participants was rather low (0.074). The scientists working with plant FA are advised to pay utmost attention to adequate and detailed description of their data acquisition protocols in their forthcoming publications.

Valkama, J. & Kozlov, M. V. (2001) Impact of climatic factors on the developmental stability of mountain birch growing in a contaminated area. Journal of Applied Ecology38, 665-673 (doi: 10.1046/j.1365-2664.2001.00628.x).

We examined fluctuating asymmetry (FA) of mountain birch leaves along a strong pollution gradient in the Kola Peninsula, north-western Russia, from 1993–2000. FA did not increase near the smelter, presumably because only pollution-resistant genets survived in heavily polluted sites. There was, however, variation in FA between years: highest values of developmental instability were recorded during the coldest summers, and birch genets differently responded to climatic fluctuations. Our results demonstrate that FA may serve as a useful measure of climatic stress in plants.


T. Cornelissen
D. E. Gavrikov
E. Haukioja
J. Junttila
J. Koricheva
M. A. Kunavin
A. D. Lama
†E. Mälkönen
J. R. Milligan
P. Niemelä
J. Valkama
B. Wilsey

Co-operating scientists

R. Ambo-Rappe
I. B. Amosova
Yu. V. Belyaeva
P. Cuevas-Reyes
F.V. Costa
O. V. Ereschenko
I. Yu. Glinyanova
E. E. Ibragimova
M. Kaligaric
B. Komac
I. S. Korotchenko
O. V. Lozinskaya
S. I. Marchenko
P. Nuche Gálvez
M. G. Opekunova
O. A. Pospelova
A. V. Rodikova
M. N. Rossi
J. C. Santos
A. S. Sarsatskaya
T. Kh. Shadmanova
E. G. Shadrina
Z. A. Simonova
E. A. Skochilova
N. A. Smirnova
V. Yu. Soldatova
O. A. Timokhina
T. Wuytack
H. Yousefzadeh


Academy of Finland
Maj and Tor Nessling Foundation