Leaf Fluctuating Asymmetry Research Articles

Leaf fluctuating asymmetry is not a reliable indicator of stress

Abstract Stress experienced during development in organisms with bilateral structures could result in developmental instability, which is expressed as subtle non‐directional deviations from perfect symmetry, known as fluctuating asymmetry (FA). As such, FA has been proposed, and extensively used, as a trait indicating stress for many organisms with bilateral structures and many types of stress. However, while this concept may apply to animals, the evidence for plants' main vegetative structures, that is, leaves, remains equivocal, and a comprehensive synthesis on this topic is still missing. We designed observational field and controlled greenhouse studies, combining different growth and leaf forms across multiple stress gradients, comprising 21 species and 80 populations. We measured FA as the difference between the left and right area of the leaf, an approach that accommodates diverse leaf forms. We used high‐precision, blind, single‐person measurements and tested for other forms of symmetry and the effect of leaf size. We further complemented our study with a systematic literature review of FA in plant leaves, compiling 51 studies comprising 72 species, 23 stress types and 131 unique entries (species × stress type). We consistently found no effect of stress on leaf FA in any of the studied species in both our field and experimental gradients. In the systematic literature review, only 39% of the unique entries showed the expected increase in FA with stress, 53% showed no effect, 9% showed an opposite trend of a decrease in FA with stress and 1% showed a unimodal relationship. Importantly, only 40% of all entries fulfilled the crucial step of controlling for a high‐precision measurement, and of these 49% reported the expected increase in FA with stress. Both the results of our observational and experimental approaches and the systematic literature review failed to support a clear relationship between stress and FA in plant leaves. These results clearly show that FA in plant leaves cannot be used as a reliable trait indicating stress during development. Read the free Plain Language Summary for this article on the Journal blog.

Leaf size is more sensitive than leaf fluctuating asymmetry as an indicator of plant stress caused by simulated herbivory

Fluctuating asymmetry (FA), defined as small, random departures away from perfect symmetry, is frequently recommended as a sensitive and universal indicator of environmental stress imposed by both abiotic and biotic factors. However, the stress sensitivities of FA and of other morphological traits are rarely compared directly. Here, we tested the hypothesis that leaf FA, rather than leaf size, is more sensitive to simulated herbivory. We performed blind measurements of FA and length of the same leaves of juvenile mountain birches (Betula pubescens var. pumila) after removal of 0, 2, 4, 8 and 16% of their leaf area during five consequent years. The leaf length in defoliated birches was 88% of that in control birches, indicating that simulated herbivory was stressful for trees. By contrast, leaf FA did not differ significantly between defoliated and control birches, despite a sufficient (91%) power of statistical analysis. Thus, leaf size, rather than leaf FA, was a more sensitive indicator of stress. This low sensitivity of FA to stress, discovered with the use of blind methods, contrasts a large pool of earlier studies, many of which have been likely influences by confirmation bias. We urge the publication of ‘negative’ or inconclusive results which currently remain underreported due to publication bias.

Associations between leaf developmental stability, variability, canalization, and phenotypic plasticity in Abutilon theophrasti.

Developmental stability, canalization, and phenotypic plasticity are the most common sources of phenotypic variation, yet comparative studies investigating the relationships between these sources, specifically in plants, are lacking. To investigate the relationships among developmental stability or instability, developmental variability, canalization, and plasticity in plants, we conducted a field experiment with Abutilon theophrasti, by subjecting plants to three densities under infertile vs. fertile soil conditions. We measured the leaf width (leaf size) and calculated fluctuating asymmetry (FA), coefficient of variation within and among individuals (CVintra and CVinter), and plasticity (PIrel) in leaf size at days 30, 50, and 70 of plant growth, to analyze the correlations among these variables in response to density and soil conditions, at each of or across all growth stages. Results showed increased density led to lower leaf FA, CVintra, and PIrel and higher CVinter in fertile soil. A positive correlation between FA and PIrel occurred in infertile soil, while correlations between CVinter and PIrel and between CVinter and CVintra were negative at high density and/or in fertile soil, with nonsignificant correlations among them in other cases. Results suggested the complexity of responses of developmental instability, variability, and canalization in leaf size, as well as their relationships, which depend on the strength of stresses. Intense aboveground competition that accelerates the decrease in leaf size (leading to lower plasticity) will be more likely to reduce developmental instability, variability, and canalization in leaf size. Increased developmental instability and intra‐ and interindividual variability should be advantageous and facilitate adaptive plasticity in less stressful conditions; thus, they are more likely to positively correlate with plasticity, whereas developmental stability and canalization with lower developmental variability should be beneficial for stabilizing plant performance in more stressful conditions, where they tend to have more negative correlations with plasticity.

Effects of Region and Elevation on Adaptation of Leaf Functional Traits of an Invasive Plant Erigeron annuus in China

A key scientific challenge relating to the threat of invasive plants on agriculture at the region level is to understand their adaptation and evolution in functional traits. Leaf functional traits, related to growth and resource utilization, might lead to adaptation of invasive plants to the geographical barriers (region or elevation). In the field experiment, we discussed the effects of region and elevation on leaf functional traits on invasive plant Erigeron annuus in farmland habitats in China. We compared leaf size, coefficient of variation (CV) of leaf traits, and fluctuating asymmetry (FA) of E. annuus from three regions (east vs. center vs. west) and two leaf types (vegetative vs. reproductive leaf), and from nine elevations (980–2100 m) in the west region of China. Our results indicated region and leaf type influenced leaf functional traits, and leaf size was significantly higher and CV of leaf traits and FA in reproductive leaves were significantly lower in the east region than in the west and center regions. Elevation and leaf type affected leaf functional traits, and leaf size was significantly higher and CV of leaf traits in reproductive leaves were significantly lower in moderate elevation. E. annuus has higher leaf size and developmental stability (lower CV and FA) in the eastern region due to the longer adaptation period. Therefore, leaf functional traits play an important role in the adaptation of different longitudes and elevations. It can also facilitate the understanding of the invasiveness and adaptation of leaf traits of invasive plants in the agricultural ecosystem during their spread process in China.

Change of Leaf Trait Asymmetry Type in Tilia cordata Mill. and Betula pendula Roth under Air Pollution

Leaf fluctuating asymmetry (FA) is widely used as an environmental stress index, including pollution. Besides FA, leaf bilateral traits can have directional asymmetry (DA) and antisymmetry (AS), which are considered hereditary. Leaf FA transitioning to DA/AS or mixed asymmetry, under air pollution, has been insufficiently investigated. This study analysed leaf asymmetry types in Tilia cordata Mill. and Betula pendula Roth under traffic air pollution over several years. In addition, the relations of such transitions to pollution, and their effect on FA-integrated index, were studied. The asymmetry types of all studied leaf traits varied with air pollution increase, as well as in control trees in different years. T. cordata most often had FA transition to DA/mixed asymmetry, while B. pendula rarely had a mixed asymmetry and FA transitions to DA/AS were observed with the same frequency. Air pollution impacted FA transitions to other asymmetry types. In most cases their frequency changed non-monotonically that corresponded to hormesis and paradoxical effects. However, FA integrated index in studied trees did not depend on change of leaf asymmetry type. Thus, DA and AS in studied plants were not exclusively hereditary. Hence, the changes of leaf asymmetry type should be considered when using leaf FA in environment assessment.

Contrasting patterns of morphology, fluctuating asymmetry and leaf herbivory in three plant species of different successional stages of a tropical dry forest

This paper shows the intraspecific plant responses in leaf morphology, herbivory and FA between mature and successional tropical dry forests, as well as the difficulty associated with understanding the relationship between FA and herbivory Understanding the processes that affect biotic interactions during secondary succession has implications for the maintenance of species diversity in the tropics. We studied the changes in leaf morphology, fluctuating asymmetry (FA) and herbivory in three dominant tropical dry forest plant species that occur in mature and secondary forests. We selected eight study sites: four in mature and four in successional forests. At each site, a plot of 20 × 50 m was established to characterize the vegetation structure and soil fertility. Subsequently, leaf morphology, FA and herbivory were measured in all individuals of Cordia elaeagnoides, C. alliodora and Achatocarpus gracilis with DBH ≥ 2.5 cm found in the plots. Plant abundance and plant height decreased in secondary forest, while the content of nitrates and phosphates increased in soil of secondary forests. Differences in leaf morphology between forest conditions were found for the three species. Total leaf area was higher in mature than in secondary forests for C. elaeagnoides and A. gracilis. An opposite pattern was found for C. alliodora. In both Cordia species, herbivory was higher in secondary than in mature forests. The opposite pattern was found for A. gracilis in secondary forests. For all the cases, FA was higher in mature forests than in secondary forests. Herbivory was positively correlated with FA in secondary forests in C. elaeganoides and in A. gracilis, whereas in C. alliodora herbivory was positively related with FA in mature forests. Overall, we detected changes in foliar morphology, fluctuating asymmetry and herbivory between mature and secondary forests, with a general pattern of higher FA levels in mature forests. Our findings illustrate the difficulty associated with understanding the relationship between FA and herbivory throughout the regeneration process in tropical dry forests due to the complexity of abiotic and biotic factors that can affect plant–herbivore interactions.

Do defoliating insects distinguish between symmetric and asymmetric leaves within a plant?

1. Plants represent a highly heterogeneous resource for herbivores. One dimension of this heterogeneity is reflected by the within‐plant variation in the leaf fluctuating asymmetry (FA), i.e. in the magnitude of the random deviations from the symmetry in leaf shape.2. This study is the first to test experimentally the hypothesis that variation in the quality of individual leaves for defoliating insects (11 species) within a plant (seven tree and shrub species) is associated with the FA of these leaves.3. It was demonstrated that specialist defoliators generally distinguish between nearly symmetric (low FA) and highly asymmetric (high FA) leaves, but do not distinguish between discs cut from these leaves. Low‐FA leaves of Salix caprea, Salix myrsinifolia and Populus tremula were of better quality for insects than high‐FA leaves, as demonstrated by both preference tests and performance trials. By contrast, high‐FA leaves of Betula pubescens were of better quality for insects than low‐FA leaves, whereas insects feeding on Alnus incana showed similar responses to high‐ and low‐FA leaves.4. It is concluded that insect herbivores can distinguish between leaves with high and low FA, and that FA may be associated with the quality of an individual leaf for insects, although the direction and strength of the effect of leaf FA on insect preference and performance vary among study systems. The ecological significance of substantial within‐plant variation in leaf FA remains to be explored.

Temperature and herbivory, but not pollution, affect fluctuating asymmetry of mountain birch leaves: Results of 25-year monitoring around the copper‑nickel smelter in Monchegorsk, northwestern Russia

Fluctuating asymmetry (FA), which is defined as the magnitude of the random deviations from a symmetrical shape, reflects developmental instability and is commonly assumed to increase under environmental and genetic stress. We monitored the leaf FA of mountain birch, Betula pubescens subsp. czerepanovii, from 1993 to 2017 in individually marked trees at 21 sites around the copper‑nickel smelter at Monchegorsk, and we then analysed the results with respect to spatial and temporal variation in pollution, climate and background insect herbivory. Responses of leaf FA to different stressors were stressor specific: FA did not correlate with pollution load, it decreased significantly with an increase in June air temperature and it increased slightly but significantly with an increase in the previous-year leaf damage due to defoliating and leafmining insects. Our findings suggest that climate warming is unlikely to impose stress on the explored mountain birch populations, but even small increases in insect herbivory may adversely affect birch trees. However, these conclusions, since they are based on an observational study, should be viewed as tentative until confirmed by controlled experiments. We also demonstrated that the use of non-blinded measurements, which are prone to confirmation bias, was the primary reason for the earlier report of an increase in birch leaf FA near the Monchegorsk smelter. We hope that our findings will promote a wide use of blinded methods in ecological research and that they will contribute to debunking the myth that plant leaf FA consistently increases with increases in environmental pollution.

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

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.

Fluctuating asymmetry of birch leaves did not increase with pollution and drought stress in a controlled experiment

Fluctuating asymmetry (FA), defined as small, non-directional deviations from perfect symmetry in morphological characters, is often recommended as a handy indicator of environmental stress. A reliance on observational data to provide empirical evidence for the effects of different stressors on FA, in combination with increasing attempts to use FA in environmental research, underscore the need for careful examination of the relationships between environmental stress and FA. We experimentally tested the hypotheses that (i) heavy metal and drought stress increase the leaf FA in plants, and that (ii) plants persisting in heavily polluted sites possess greater stress tolerance and therefore show smaller increases in leaf FA in response to heavy metals than do plants from unpolluted sites. We collected mountain birch, Betula pubescens subsp. czerepanovii, seeds from eight polluted and ten unpolluted sites and reared the seedlings in a sophisticated greenhouse (phytotron). We compared leaf FA between control seedlings, seedlings irrigated with water containing copper and nickel sulphates, and seedlings exposed to drought. Leaf FA showed no response to either heavy metals or drought, despite significant impacts of these treatments on seedling height, leaf size and photosynthetic efficiency. This FA result was independent of the level of pollution at the site of seed origin and consistent for FA values based on low and high accuracy measurements of leaf width, as well as for FA values based on measurements of the widths and areas of leaf halves. Our findings add to accumulating evidence regarding inconsistent relationships between FA and abiotic stress, thereby questioning the indicatory value of FA. We strongly recommend that the use of FA as an indicator of environmental stress be limited to study systems for which the existence of cause-and-effect relationship between the stressing impact and the changes in FA is confirmed by controlled, blinded experiments.

Fluctuating asymmetry of leaves is a poor indicator of environmental stress and genetic stress by inbreeding in Silene vulgaris

Fluctuating asymmetry (FA) is often used as a measure of developmental instability and has been proposed as an indicator of both environmental and genetic stress. However, the empirical evidence for the effects of stress on FA in plants is inconsistent, and there are few controlled experimental studies. We analyzed different distance- and shape-based measures of the fluctuating asymmetry of the leaves of clonally replicated self- and cross-pollinated lineages of Silene vulgaris (Moench) Garcke (Caryophyllaceae) grown under a control and seven different stress treatments (drought, copper, simulated herbivory, and two levels of nutrient deficiency and of shade). Overall, FA differed among stress treatments, but was not generally higher under stress and even reduced in some treatments. Different measures of FA were only weakly correlated. Inbreeding increased only one measure of leaf FA, and only under high stress intensities. Our findings suggest that in S. vulgaris leaf fluctuating asymmetry does not serve as an indicator of environmental stress or of genetic stress by inbreeding.

Reproducibility of fluctuating asymmetry measurements in plants: Sources of variation and implications for study design

Fluctuating asymmetry (FA), i.e. small, non-directional deviations from perfect symmetry in morphological characters, increases under genetic and/or environmental stress. Ecological and evolutionary studies addressing FA became popular in past decades; however, their outcomes remain controversial. The discrepancies might be at least partly explained by inconsistent and non-standardised methodology. Our aim was to improve the methodology of these studies by identifying factors that affect the reproducibility of FA measurements in plant leaves. Six observers used a highly standardised measurement protocol to measure FA using the width, area and weight of the same set of leaves of 10 plant species that differed in leaf size, shape of the leaf margin and other leaf traits. On average, 24% of the total variation in the data was due to measurement error. Reproducibility of measurements varied with the shape of leaf margin, leaf size, the measured character and the experience of the observer. The lowest reproducibility of the width of leaf halves was found for simple leaves with serrate margins and the highest for simple leaves with entire margins and for compound pinnate leaves. The reproducibility was significantly lower for the weight of leaf halves than for either their width or area, especially for plants with small leaves. The reproducibility was also lower for measurements made by experienced observers than by naïve observers. The size of press-dried leaves decreased slightly but significantly relative to fresh leaves, but the FA of press-dried leaves adequately reflected the FA of fresh leaves. In contrast, preservation in 60% ethanol did not affect leaf size, but it decreased the width-based values of FA to 89.3% of the values measured from fresh leaves. We suggest that although reproducibility of leaf FA measurements depends upon many factors, the shape of the leaf margin is the most important source of variation. We recommend, whenever possible, choosing large-leaved plants with entire leaf margins as model objects for studies involving measurements of FA using the width of leaf halves. These measurements should be conducted with high accuracy from images of fresh or press-dried leaves.

Herbivory-induced stress: Leaf developmental instability is caused by herbivore damage in early stages of leaf development

Herbivory is a major source of plant stress and its effects can be severe, decreasing plant fitness, or subtle, affecting the development of leaves by influencing the normal pattern of growth and expansion of leaf blades. Fluctuating asymmetry (FA) analysis is recognized as a measure of plant stress, and can be used to evaluate subtle effects of herbivory on the imperfect growth of bilaterally symmetrical traits, such as leaves. One general issue is that authors usually consider FA as an indicator of stress, which can attract herbivores (plant stress hypothesis), and studies showing that herbivores themselves affect leaf symmetry (herbivory-induced stress hypothesis) are scarce, with mixed results. Here, we investigated the relationship between herbivory by thrips and leaf FA in Banisteriopsis malifolia and Heteropterys escallonifolia (Malpighiaceae). Pseudophilothrips obscuricornis is a free-living, non-pest, sucking species that feeds mainly on leaf buds. We hypothesized that herbivory by thrips in the early stages of leaf development would provoke increased FA levels in mature leaves. The results showed that thrips herbivory rate was low, affecting barely more than 1% of the leaf blade. Nonetheless, thrips-attacked leaves of B. malifolia and H. escallonifolia presented increases of 15 and 27% in leaf asymmetry, respectively, compared to uninjured leaves, corroborating the herbivory-induced stress hypothesis. Since herbivory by thrips in leaf buds was related to significant increases in the stress of mature leaves, we assume that under these circumstances, FA can be used as a biomarker for plant stress following herbivory damage. To be useful as a biomarker of stress, FA in plants must be investigated with caution, taking into account the natural history of the herbivore species and timing of leaf damage.

Leaf Fluctuating Asymmetry and Herbivory of Tibouchina heteromalla in Restored and Natural Environments.

Fluctuating asymmetry (FA) is a parameter to measure developmental stability in plants, which can be altered by disturbances, pollution, and biotic factors such as herbivory. We evaluated the effects of environmental stress and herbivory on the FA levels in individuals of Tibouchina heteromalla (Melastomataceae) that occur in natural and undergoing restoration areas in rupestrian grasslands at Serra do Cipó, Brasil. Individuals were collected and measured in seven restored and five natural areas, totalizing 240 individuals. We found that individuals in restored areas had greater leaf area, higher levels of insect herbivory and FA compared to individuals that occurred in natural areas. In both environments, the proportion of individuals with leaf damage caused by herbivory was higher than the proportion of undamaged individuals. In addition, FA was positively correlated with herbivory and total leaf area in both restored and natural areas. These results suggest that more favorable conditions in the restored areas enhanced leaf growth, resulting in higher FA.

Confirmation bias in studies of fluctuating asymmetry

Fluctuating asymmetry (FA) represents small, non-directional deviations from perfect symmetry in morphological characters. FA is generally accepted to increase in response to stress; therefore, FA is frequently used in ecological studies as an index of stress experienced by an organism, in particular due to environmental pollution. We experimentally tested the hypothesis that the outcomes of studies based on FA measurements may have been influenced by confirmation bias, i.e. the tendency of humans to seek out evidence in a manner that confirms their hypotheses and beliefs. We collected 100 leaves of downy birch (Betula pubescens) from a single tree, grouped them haphazardly into ten samples, scanned every sample, and then asked each of 31 scientists (experienced in studying FA) to measure FA from the scanned images of all 100 leaves. Three groups of participants were provided with false information about the origin of each sample and about the hypothesis to be tested, and one group (control) was provided with true information. 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. When the participants were told that half the samples originated from a polluted site and half from a clean site and were asked to attribute each sample to either of these sites based on leaf FA, the differences in FA between samples classified as ‘polluted’ and ‘unpolluted’ were much higher than the differences obtained from measurements of the same sets of samples made by the control group. We conclude that when scientists expected to find high FA in some samples, the results of their measurements confirmed their expectations. This effect, classified as confirmation bias, may considerably influence the outcomes of the research on FA. This confirmation bias can be avoided by using a blind method, where the person conducting measurements is not aware of the origin of samples being measured. We argue that the use of blind methods is critically important for any study addressing environmental or genetic impacts on FA.

Application of fluctuating asymmetry indexes of silver birch leaves for diagnostics of plant communities under technogenic pollution

The prospects for applying the fluctuating asymmetry (FA) of silver birch (Betula pendula Roth) leaves for diagnosis of plant community conditions in technogenically polluted environments are considered with an example of the effect of heavy metals and chronic ionizing radiation. An increase in the minimum sample size to 150–180 leaves and measurements of morphometric traits with an improved accuracy of 0.06–0.07 mm made it possible to overcome the influence of sample size on FA parameters. The excess content of nickel (18.5 times with respect to the background level), lead (16.0 times), manganese (5.8 times), and copper (3.0 times) in birch leaves was accompanied by the increase in multivariate FA index by 20.0%. The chronic exposure to ionizing radiation (at absorbed dose rate on the soil surface of 4.74 µGy/h) elevated the multi-variate FA index of leaves by 29.8% and the content of chlorophylls a and b in leaves by 50.3 and 82.9%, respectively. It was found that the most informative morphometric trait for analysis of birch leaf FA is the distance between the bases of the first and second lateral veins; its FA index rose to 40.4% under the influence of heavy metals and to 53.6% under exposure to chronic ionizing radiation. Thus, FA can be regarded as a sensitive biomarker for detecting early negative responses of forest ecosystems to technogenic pollution.

The effect of fluctuating asymmetry and leaf nutrients on gall abundance and survivorship

Fluctuating asymmetry (FA) is defined as small and random deviations from perfect symmetry in otherwise bilaterally symmetrical traits. Usually, plants under stress have a higher nutritional quality and are preferred by insect herbivores. Here, we examined the relationship among leaf FA of Bauhinia brevipes (Fabaceae), nutrients and the occurrence of Schizomyia macrocapillata (Cecidomyiidae: Diptera). We evaluated whether: (i) FA was related to S. macropillata abundance and survivorship; (ii) FA correlated with the levels of foliar nutrients (macro- and micronutrients, and organic carbon); and (iii) S. macropillata abundance was related to leaf nutrients. The results showed a positive relationship between FA and gall abundance. S. macrocapillata survivorship was five times higher in B. brevipes individuals with high FA levels, but this difference was not significant. The influence of nutrients in B. brevipes FA was negligible, except for foliar nitrogen, which was 7.3% higher in plants with low FA levels. The abundance of S. macrocapillata was negatively related to nitrogen levels, but gall survivorship was not affected by this nutrient. We found evidence for a causal relationship between FA and gall occurrence, since S. macropillata gall oviposition occurs in young undeveloped leaves, thus mature leaves show an increase in FA. Nonetheless, in this system, neither FA nor nitrogen influenced gall survivorship.

Fluctuating asymmetry and herbivory in two ontogenetical stages of Chamaecrista semaphora in restored and natural environments

Reintroduced environments represent stressful conditions to plants that can be observed in different ways. We evaluated the relationships between fluctuating asymmetry (FA), herbivory, and plant ontogeny of Chamaecrista semaphora (Fabaceae) under natural and restored habitat conditions. The patterns of leaf FA and herbivory by folivorous insects (chewing) on saplings and mature plants in each habitat were determined. No relationship was found between FA and herbivory on the two ontogenetic stages in both environments, suggesting that FA did not represent an indicator of stress. The frequency and amount of leaf area removed by folivores were higher in saplings compared to adult plants under the natural habitat, while the opposite trend was observed on restored habitat for adult plants. The restored habitat did not represent an environmental stress condition to C. semaphora, indicating that this endemic plant may represent a good candidate to restoration programs in harsh environments. However, we observed great differences in leaf FA and herbivory among individuals within habitats. Knowledge on plant quality, competition, physiology, and interactions with natural enemies are highly needed to support long lasting programmes on restoration of harsh environments.

Variación fenotípica y fluctuación de la asimetría de la hoja en una población natural de Parrotia persica (Hamamelidaceae), una especie endémica del bosque hircaniano (Iran)

Se evaluó la variación fenotípica en cuatro poblaciones naturales de Parrotia persica (Hamamelidaceae), una especie endémica considerada como un fósil viviente del bosque hircaniano, a través de un análisis morfométrico y multivariado de las hojas. Asimismo, se estudiaron la plasticidad y la asimetría foliar fluctuante (AFF). Nuestros hallazgos mostraron claramente una divergencia significativa entre sitios. El tamaño más pequeño de la lámina foliar, la plasticidad más grande y los valores más pequeños de AFF fueron registrados en los sitios más xéricos de la parte oriental (Ghorogh y Daland), por lo que parece que estos sitios están sujetos a un mayor estrés ambiental. Obtuvimos resultados interesantes, pero hace falta realizar nuevos estudios de la diversidad de aloenzimas y ADN.

Contrasting herbivory patterns and leaf fluctuating asymmetry inHeliocarpus pallidusbetween different habitat types within a Mexican tropical dry forest

Abstract:Leaf fluctuating asymmetry (FA) is considered an important indicator of environmentally induced stress in plants, but the relationship between herbivory and FA levels is not clear. In this study we compared leaf size and shape, leaf area consumed by herbivorous insects, and FA levels between individuals ofHeliocarpus pallidus(Tiliaceae) from two adjacent and contrasting habitat types (deciduous and riparian) in the Chamela–Cuixmala tropical dry-forest biosphere reserve. Ten individuals ofH. palliduswere collected in each habitat type. Leaf shape was assessed using geometric morphometric techniques. Results indicated statistically significant differences in leaf shape between individuals from the two habitat types. In individuals from the riparian habitat leaf area (mean = 42.3 ± 1.2 cm2), herbivory levels (mean = 25.5% ± 1.8%) and FA levels (mean = 0.38 ± 0.04 cm) were significantly higher than in individuals from the deciduous habitat (17.2 ± 3.5 cm2; 9.6% ± 1.0% and 0.18 ± 0.04 cm, respectively). Within habitats, significant correlations were found between total leaf area and percentage leaf area removed by insects (R2= 0.92 in riparian habitats,R2= 0.9 in deciduous habitats), and between percentage leaf area removed and FA (R2= 0.70 in riparian habitats,R2= 0.79 in deciduous habitats). As has been suggested for other plant species, it is possible that the more favourable conditions in the riparian habitat enhance leaf growth, resulting in higher FA. Also, individuals in this habitat might be characterized by lower chemical defence and/or higher nutritional quality, which would explain the higher herbivory levels.