Local Insect Damage Reduces Fluctuating Asymmetry in Next-year’s Leaves of Downy Birch

Mikhail Kozlov,Elena Zvereva,Dmitry Gavrikov,Vitali Zverev

doi:10.3390/insects9020056

Abstract

Insect herbivory imposes stress on host plants. This stress may cause an increase in leaf fluctuating asymmetry (FA), which is defined as the magnitude of the random deviations from a symmetrical leaf shape. We tested the hypothesis that differences in leaf FA among individual shoots of downy birch, Betula pubescens, are at least partly explained by local damage caused by insects in the previous year. Unexpectedly, we found that in the year following the damage imposed by miners, leafrollers and defoliators, damaged birch shoots produced leaves with lower FAs compared to shoots from the same tree that had not been damaged by insects. This effect was consistent among the different groups of insects investigated, but intra-species comparisons showed that statistical significance was reached only in shoots that had been damaged by the birch leaf roller, Deporaus betulae. The detected decrease in leaf FA in the year following the damage agrees with the increases in shoot performance and in antiherbivore defence. The present results indicate that within-plant variation in leaf FA may have its origin in previous-year damage by insects, and that FA may influence the current-year’s distribution of herbivory.

Highlights

Trees are modular organisms consisting of repetitive multicellular semi-independent units, such as leaves, shoots, branches, stems and roots
The present results indicate that within-plant variation in leaf fluctuating asymmetry (FA) may have its origin in previous-year damage by insects, and that FA may influence the current-year’s distribution of herbivory
The previous year’s losses of foliage to insects (Table S1) were significantly higher in the mixed model ANOVA indicated that measurement error (ME5) accounted for 0.5% of the variation experimental in FA.shoots than in the control shoots (Table 1; mean ± S.E.: 16.3 ± 1.9% and 2.0 ± 0.4%, respectively)

Summary

Introduction

Trees are modular organisms consisting of repetitive multicellular semi-independent units, such as leaves, shoots, branches, stems and roots. Previous studies demonstrated that local damage experienced by one leaf or several leaves of the same shoot may cause shoot-specific responses in the year following the damage, and that these responses can contribute to intra-plant heterogeneity in leaf quality for insect herbivores [2,3]. Insect damage inflicted on leaves of an individual shoot can decrease the probability of herbivore attack on the year’s foliage produced by the same shoot, compared with attacks on shoots of the same tree that had not suffered insect damage in the previous year. The following year’s leaves, from shoots that previously experienced herbivore damage, exhibit a higher level of antiherbivore defences [3]. The cues used by plant-feeding insects to avoid these shoots that have been damaged in the previous year remain to be established

Methods

Results

Conclusion