Evaluation of leaf features in forest trees: Methods,techniques, obtainable information and limits

Tree leaves are interfaces between the whole organism and the environment. Leaves display a series of attributes that are linked to specific functions (functional leaf traits—FLT) and/or show responses to biotic and abiotic stress factors (stress response traits, SRT), which can be subdivided into: (a) morphological traits; (b) chemical traits; (c) physiological traits; (d) symptoms. The analysis of FLT is a useful tool for tree species and provenance phenotyping, due to the adaptation of trees to environmental stress. Additionally, FLT can be used as response factor in long term and large spatial scales surveys of forest conditions. Despite these potential benefits of leaf traits in the assessment of ecosystem health and functioning, leaf sampling in forests is time-consuming and costly, especially in forests with a complex vertical and horizontal structure and in remote forest areas. Once a foliar sample has been collected, many different analyses can be carried out; however, analyses should be technically simple and able to be performed within one day following the leaf collection (i.e., on fresh samples), or after air-drying the leaves themselves (analysis of dried specimens). This paper reports the results of leaf sampling and foliar analyses carried out in previous research projects and revises the current state-of-the-art. The leaf traits that are easily obtainable from leaf sampling are listed, together with the operational procedures necessary for their measurement, described in a standardized protocol. Their ecological and functional relevance is discussed in relation to their potential information (as indicators of climatic stress, drought, air and soil pollution, tree light-use and competition, plant nutritional status, health and general plant stress conditions). Finally, this review provides suggestions for the elaboration and reporting of data, and proposes some guidelines to improve the effectiveness of foliar analysis in the assessment of forest ecosystem health, properties and functioning.     

What does the fruitless gene tell us about nature vs. nurture in the sex life of Drosophila?

The fruitless (fru) gene in Drosophila has been proposed to play a master regulator role in the formation of neural circuitries for male courtship behavior, which is typically considered to be an innate behavior composed of a fixed action pattern as generated by the central pattern generator. However, recent studies have shed light on experience-dependent changes and sensory-input-guided plasticity in courtship behavior. For example, enhanced male-male courtship, a fru mutant “hallmark,” disappears when fru-mutant males are raised in isolation. The fact that neural fru expression is induced by neural activities in the adult invites the supposition that Fru as a chromatin regulator mediates experience-dependent epigenetic modification, which underlies the neural and behavioral plasticity.     

Coupling Neuropeptide Levels to Structural Plasticity in Drosophila Clock Neurons

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Large‐scale gene expression reveals different adaptations of Hyalopterus persikonus to winter and summer host plants

Host alternation, an obligatory seasonal shifting between host plants of distant genetic relationship, has had significant consequences for the diversification and success of the superfamily of aphids. However, the underlying molecular mechanism remains unclear. In this study, the molecular mechanism of host alternation was explored through a large‐scale gene expression analysis of the mealy aphid Hyalopterus persikonus on winter and summer host plants. More than four times as many unigenes of the mealy aphid were significantly upregulated on summer host Phragmites australis than on winter host Rosaceae plants. In order to identify gene candidates related to host alternation, the differentially expressed unigenes of H. persikonus were compared to salivary gland expressed genes and secretome of Acyrthosiphon pisum. Genes involved in ribosome and oxidative phosphorylation and with molecular functions of heme–copper terminal oxidase activity, hydrolase activity and ribosome binding were potentially upregulated in salivary glands of H. persikonus on the summer host. Putative secretory proteins, such as detoxification enzymes (carboxylesterases and cytochrome P450s), antioxidant enzymes (peroxidase and superoxide dismutase), glutathione peroxidase, glucose dehydrogenase, angiotensin‐converting enzyme, cadherin, and calreticulin, were highly expressed in H. persikonus on the summer host, while a SCP GAPR‐1‐like family protein and a salivary sheath protein were highly expressed in the aphids on winter hosts. These results shed light on phenotypic plasticity in host utilization and seasonal adaptation of aphids.     

No geographic variation in thermoregulatory colour plasticity and limited variation in heat‐avoidance behaviour in Battus philenor caterpillars

Phenotypic plasticity can help organisms cope with variation in their current environment, including temperature variation, but not all environments are equally variable. In the least variable or extreme environments, plasticity may no longer be used. In this case, the plasticity could be lost altogether, or it could persist with either the same or an altered reaction norm, depending on factors such as the plasticity's costs. In the pipevine swallowtail caterpillar (Battus philenor), I tested for changes in two forms of heat‐avoidance plasticity, colour change and refuge‐seeking behaviour, across the species’ range in the United states, including the cooler eastern parts of its range where colour change has not been observed and is unlikely to be needed. I found that both heat‐avoidance behaviour and colour change persisted in all surveyed populations. Indeed, the reaction norm for colour change remained nearly unaltered, whereas the threshold for refuge‐seeking only changed slightly across populations. These results suggest that the costs of these plastic traits are low enough for them to be maintained by whatever minimal gene flow the population receives. I show that plasticity can be maintained unaltered in populations where it is not used and discuss the potential consequences of this persistence for both the ecology and evolution of plasticity.     

A complex species complex: The controversial role of ecology and biogeography in the evolutionary history of Syllis gracilis Grube, 1840 (Annelida,Syllidae)

The cryptic diversity in the polychaete Syllis gracilis Grube, 1840, in the Mediterranean Sea was examined with an integrative morpho-molecular approach. Individuals of S. gracilis were collected at eleven Mediterranean localities to provide an insight into the role of brackish environments in inducing cryptic speciation. The examination of morphological features combined with a molecular genetic analysis based on a partial sequence of the 16S rRNA gene highlighted discrepancies between morphological and molecular diversity. Morphological data allowed to identify a morphotype with short appendages occurring in coralline algae communities and another one with long appendages observed in brackish-water environments and Sabellaria reefs. Multivariate analyses showed that sampling localities were the greatest source of morphological divergence, suggesting that phenotypic plasticity may play a role in local adaptations of S. gracilis populations. Molecular data showed the occurrence of four divergent lineages not corresponding to morphological clusters. Different species delimitation tests gave conflicting results, retrieving, however, at least four separated entities. Some lineages occurred in sympatry and were equally distributed in marine and brackish-water environments, excluding a biogeographic or ecological explanation of the observed pattern and suggesting instead ancient separation between lineages and secondary contact. The co-occurrence of different lineages hindered the identification of the lineage corresponding to S. gracilis sensu stricto. The discrepancy between morphological and molecular diversity suggests that different environmental and biogeographic features may interact in a complex and unpredictable way in shaping diversity patterns. An integrative approach is needed to provide a satisfactory insight on evolutionary processes in marine invertebrates.     

Increase in body size is correlated to warmer winters in a passerine bird as inferred from time series data

Climate change is expected to affect natural populations in many ways. One way of getting an understanding of the effects of a changing climate is to analyze time series of natural populations. Therefore, we analyzed time series of 25 and 20 years, respectively, in two populations of the citril finch (Carduelis citrinella) to understand the background of a dramatic increase in wing length in this species over this period, ranging between 1.3 and 2.9 phenotypic standard deviations. We found that the increase in wing length is closely correlated to warmer winters and in one case to rain in relation to temperature in the summer. In order to understand the process of change, we implemented seven simulation models, ranging from two nonadaptive models (drift and sampling), and five adaptive models with selection and/or phenotypic plasticity involved and tested these models against the time series of males and females from the two population separately. The nonadaptive models were rejected in each case, but the results were mixed when it comes to the adaptive models. The difference in fit of the models was sometimes not significant indicating that the models were not different enough. In conclusion, the dramatic change in mean wing length can best be explained as an adaptive response to a changing climate.     

Variation in growth form in relation to spectral light quality (red/far-red ratio) in Plantago lanceolata L. in sun and shade populations

Plants from a sun and shade population were grown in two environments differing in the ratio of red to far-red light (R/FR ratio). A low R/FR ratio, simulating vegetation shade, promoted the formation of long, upright-growing leaves and allocation towards shoot growth, whereas a high R/FR ratio had the opposite effects. The increase in plant height under the low R/FR ratio was accompanied by a reduction in the number of leaves. Population differences in growth form resembled the differences between plants grown in different light environments: plants from the shade population had rosettes with long erect leaves, whereas plants from the sun population formed prostrate rosettes with short leaves. Plants from the shade population were more responsive to the R/FR ratio than plants from the sun population: the increases in leaf length, plant height, and leaf area ratio under a low R/FR ratio were larger in the shade population. However, differences in plasticity were small compared to the population difference in growth form itself. We argue that plants do not respond optimally to shading and that developmental constraints might have limited the evolution of an optimal response. Received: 8 December 1996 / Accepted: 31 March 1997