Effects of stress and rapid growth on fluctuating asymmetry and insect damage in birch leaves

We studied how fluctuating asymmetry (FA), which is commonly used as an non -specific stress indicator, is influenced by abiotic stress along a moistur e gradient and by rapid growth, i.e. the production of larger than normal l eaves after simulated browsing, in white birch (Betula pubescens) growing i n a mire. Variation of abiotic stress (plots near vs far from open, wet bou ndary of tree stand) was obvious as interpreted from smaller leaf size and lower stature of trees growing closest to the wettest, open center of the m ire. However. we did not find increased leaf FA near the wettest area, poss ibly because of the high background level of stress in the mire habitat or the presence of flood-tolerant genotypes. Simulated winter browsing increased leaf size in the following growing seas on, and the strength of the response increased with the severity of the bro wsing treatment. Likewise, larger leaves of browsed ramets had higher devel opmental instability, as measured by size-corrected FA. Moreover, the effec ts of simulated winter browsing on FA were proportionally greater than the size effects in expanding leaves. Simulated winter browsing also increased insect damage incurred by leaves. Our results demonstrate that, in addition to previously shown effects of st ress, excess leaf growth can also increase developmental instability and FA . We also demonstrated a higher rate of developmental errors in the later t han early stages of leaf expansion.