Early environment influences later performance in fishes

Conditions fish encounter during embryogenesis and early life history can leave lasting effects not only on morphology, but also on growth rate, life‐history and behavioural traits. The ecology of offspring can be affected by conditions experienced by their parents and mother in particular. This review summarizes such early impacts and their ecological influences for a variety of teleost species, but with special reference to salmonids. Growth and adult body size, sex ratio, egg size, lifespan and tendency to migrate can all be affected by early influences. Mechanisms behind such phenotypically plastic impacts are not well known, but epigenetic change appears to be one central mechanism. The thermal regime during development and incubation is particularly important, but also early food consumption and intraspecific density can all be responsible for later life‐history variation. For behavioural traits, early experiences with effects on brain, sensory development and cognition appear essential. This may also influence boldness and other social behaviours such as mate choice. At the end of the review, several issues and questions for future studies are given.     

Elevated volatile concentrations in high‐nutrient plants: do insect herbivores pay a high price for good food?

1. A tritrophic perspective is fundamental for understanding the drivers of insect–plant interactions. While host plant traits can directly affect insect herbivore performance by either inhibiting or altering the nutritional benefits of consumption, they can also have an indirect effect on herbivores by influencing rates of predation or parasitism. 2. Enhancing soil nutrients available to trees of the genus Eucalyptus consistently modifies plant traits, typically improving the nutritional quality of the foliage for insect herbivores. We hypothesised that resulting increases in volatile essential oils could have an indirect negative effect on eucalypt‐feeding herbivores by providing their natural enemies with stronger host/prey location cues. 3. Eucalyptus tereticornis Smith seedlings were grown under low‐ and high‐nutrient conditions and the consequences for the release of volatile cues from damaged plants were examined. The influence of 1,8‐cineole (the major volatile terpene in many Eucalyptus species) on rates of predation on model caterpillars in the field was then examined. 4. It was found that the emission of cineole increased significantly after damage (artificial or herbivore), but continued only when damage was sustained by herbivore feeding. Importantly, more cineole was emitted from high‐ than low‐nutrient seedlings given an equivalent amount of damage. In the field, predation was significantly greater on model caterpillars baited with cineole than on unbaited models. 5. These findings are consistent with the hypothesis that any performance benefits insect herbivores derive from feeding on high‐nutrient eucalypt foliage could be at least partially offset by an increased risk of predation or parasitism via increased emission of attractive volatiles.     

Principles and pitfalls in designing site-directed peptide ligands

An immunoglobulin light chain dimer with a large generic binding cavity was used as a host molecule for designing a series of peptide guest ligands. In a screening procedure peptides coupled to solid supports were systematically tested for binding activity by enzyme linked immunosorbent assays (ELISA). Key members of the binding series were synthesized in milligram quantities and diffused into crystals of the host molecule for X-ray analyses. These peptides were incrementally increased in size and affinity until they nearly filled the cavity. Progressive changes in binding patterns were mapped by comparisons of crystallo-graphically refined structures of 14 peptide–protein complexes at 2.7 Å resolution. These comparisons led to guidelines for ligand design and also suggested ways to modify previously established binding patterns. By manipulating equilibria involving histidine, for example, it was possible to abolish one important intramolecular interaction of the bound ligand and substitute another. These events triggered a change inconformation of the ligand from a compact to an extended form and a comprehensive change in the mode of binding to the protein. In dipeptides of histidine and proline, protonation of both imidazolium nitrogen atoms was used to program anend-to-end reversal of the direction in which the ligand was inserted into the binding cavity. Peptides cocrystallized with proteins produced complexes somewhat different in structure from those in which ligandswere diffused into preexisting crystals. In sucha large and malleable cavity, space utilization was thus different when a ligand was introduced before the imposition of crystal packing restraints. © 1993 Wiley-Liss, Inc.     

Bisphenol A and Risk Management Ethics

It is widely recognized that endocrine disrupting compounds, such as Bisphenol A, pose challenges for traditional paradigms in toxicology, insofar as these substances appear to have a wider range of low‐dose effects than previously recognized. These compounds also pose challenges for ethics and policymaking. When a chemical does not have significant low‐dose effects, regulators can allow it to be introduced into commerce or the environment, provided that procedures and rules are in place to keep exposures below an acceptable level. This option allows society to maximize the benefits from the use of the chemical while minimizing risks to human health or the environment, and it represents a compromise between competing values. When it is not possible to establish acceptable exposure levels for chemicals that pose significant health or environmental risks, the most reasonable options for risk management may be to enact either partial or complete bans on their use. These options create greater moral conflict than other risk management strategies, leaving policymakers difficult choices between competing values.     

Tests of associational defence provided by hairy plants for glabrous plants of Arabidopsis halleri subsp. gemmifera against insect herbivores

1. Trichome‐producing (hairy) and trichomeless (glabrous) plants of Arabidopsis halleri subsp. gemmifera were investigated to test whether plant resistance to herbivory depends on the plants' phenotypes and/or the phenotypes of neighbouring plants (associational effects). 2. A common garden experiment was conducted in which the relative frequency of hairy and glabrous plants was manipulated. Two species of leaf‐chewing insects (larvae of a white butterfly and a cabbage sawfly) were found less often on hairy plants than on glabrous plants. By contrast, the numbers of aphids and flea beetles did not differ significantly between hairy and glabrous plants. For none of these insects did abundance depend on the frequency of the two plant morphs. 3. A field survey was conducted in two natural populations of A. halleri. In the first population, a species of white butterfly was the dominant herbivore, and hairy plants incurred less leaf damage than glabrous plants across 2 years. By contrast, in the other population, where flea beetles were dominant, there were no consistent differences in leaf damage between the two types of plants. In neither of the two populations was any evidence found of associational effects. 4. This study did not provide any conclusive evidence of associational effects of anti‐herbivore resistance, but it was discovered that trichomes can confer resistance to certain herbivores. Given the results of previous work by the authors on associational effects against a flightless leaf beetle, such associational effects of the trichome dimorphism of A. halleri were herbivore‐specific.     

Biochemical and populational responses of an aquatic bioindicator species,Daphnia longispina,to a commercial formulation of a herbicide (Primextra® Gold TZ) and its active ingredient (S-metolachlor)

The growing demand of human populations for food supplies has led to an increase in the use of synthetic products, mainly pesticides, which induce adverse effects not only to target organisms, but also to non-target biota of agroecosystems. Aquatic ecosystems in the proximity of agricultural areas are particularly vulnerable to pesticides, which cause underperformance or extinction of non-target sensitive species. Once in the aquatic system, these chemicals can affect biological processes at multiple levels (molecular, individual, populational), causing ecosystem imbalance across multiple scales. In this study, the effect of a commercial formulation of a herbicide (Primextra® Gold TZ) and its main active ingredient (a.i., S-metolachlor) was studied on a freshwater cladoceran species (Daphnia longispina), at different levels of biological organization and temporal scales. S-metolachlor is used in many herbicide formulations applied in corn/maize cultures, which is a relevant culture worldwide. As a first step, the acute and chronic effects of both commercial formulation and a.i. were quantified, and both formulations negatively affected the cladoceran's survival and reproductive parameters (age at first reproduction, number of offspring and number of broods), as well as the population's rate of increase. Whilst acute effects were comparable, the commercial formulation was slightly more toxic (EC₅₀ was two-times lower) than the a.i. in chronic exposures, being prejudicial to D. longispina populations above 4.0 mg/L of S-metolachlor. In a second experimental step, we focused on the potential multi-generational impacts of the exposure to the a.i. alone on biochemical (lipid biomarkers, namely fatty acids) and populational responses, because of the relevance of S-metolachlor as a biosynthesis inhibitor in many herbicidal formulations. The herbicide caused a significant decrease in Daphnia fecundity (in the size of the 1st clutch), but no concomitant alterations were found in fatty acid profiles of mothers or offspring. More important, this experiment showed that S-metolachlor did not cause effects in the subsequent generation, thus suggesting that biotic communities may recover after exposure to the xenobiotic.