Predation on mutualists can reduce the strength of trophic cascades

Ecologists have put forth several mechanisms to predict the strength of predator effects on producers (a trophic cascade). We suggest a novel mechanism – in systems in which mutualists of plants are present and important, predators can have indirect negative effects on producers through their consumption of mutualists. The strength of predator effects on producers will depend on their relative consumption of mutualists and antagonists, and on the relative importance of each to producer population dynamics. In a meta-analysis of experiments that examine the effects of predator reduction on the pollination and reproductive success of plants, we found that the indirect negative effects of predators on plants are quite strong. Most predator removal experiments measure the strength of predator effects on producers through the antagonist pathway; we suggest that a more complete understanding of the role of predators will be achieved by simultaneously considering the effects of predators on plant mutualists.     

The genetics of adaptation: the roles of pleiotropy, stabilizing selection and drift in shaping the distribution of bidirectional fixed mutational effects

Pleiotropy allows for the deterministic fixation of bidirectional mutations: mutations with effects both in the direction of selection and opposite to selection for the same character. Mutations with deleterious effects on some characters can fix because of beneficial effects on other characters. This study analytically quantifies the expected frequency of mutations that fix with negative and positive effects on a character and the average size of a fixed effect on a character when a mutation pleiotropically affects from very few to many characters. The analysis allows for mutational distributions that vary in shape and provides a framework that would allow for varying the frequency at which mutations arise with deleterious and positive effects on characters. The results show that a large fraction of fixed mutations will have deleterious pleiotropic effects even when mutation affects as little as two characters and only directional selection is occurring, and, not surprisingly, as the degree of pleiotropy increases the frequency of fixed deleterious effects increases. As a point of comparison, we show how stabilizing selection and random genetic drift affect the bidirectional distribution of fixed mutational effects. The results are then applied to QTL studies that seek to find loci that contribute to phenotypic differences between populations or species. It is shown that QTL studies are biased against detecting chromosome regions that have deleterious pleiotropic effects on characters.     

Effects of corticotropin releasing hormone on appetitive behaviors.

Corticotropin releasing hormone (CRH) is a 41-residue hypothalamic neuropeptide that has been shown to have potent behavioral effects in animals and has been implicated in clinical disorders in man. This review focuses on those aspects of the behavioral effects of CRH related to food-associated behaviors. The effects of CRH on food intake are compared with its effects on performances maintained by food presentation, and contrasted with the effects of CRH on performances maintained by other events. The effects of CRH antagonists and drugs that interact with the behavioral effects of CRH are also reviewed, particularly with respect to their direct effects on food intake. Lastly, data assessing the effects of CRH administration on central neurotransmitter levels are presented and compared with levels seen in clinical populations. The effect of CRH on food intake seen in animals is consistent with a putative role for CRH in clinical syndromes where appetite suppression is apparent. Since some of the effects of CRH on food intake are subject to pharmacological intervention, strategies directed at peptidergic mechanisms of psychiatric disorders should be explored.     

Effects of Single P-Element Insertions on Bristle Number and Viability in Drosophila Melanogaster

Single P-element mutagenesis was used to construct 1094 lines with P[lArB] inserts on all three major chromosomes in an isogenic background previously free of P elements. The effects of insertions on bristle number and on viability were assessed by comparison to 392 control lines. The variance and effects of P-element inserts on bristle number and viability were larger than those inferred from spontaneous mutations. The distributions of effects on bristle number were symmetrical and highly leptokurtic, such that a few inserts with large effects caused most of the increase in variance. The distribution of effects on viability were negatively skewed and platykurtic. On average, the effects of P-element insertions on bristle number were partly recessive and on viability were completely recessive. P-element inserts with large effects on bristle number tended to have reduced viability, but the correlation between the absolute value of the effects on bristle number and on viability was not strong. Fifty P-element inserts tagging quantitative trait loci (QTLs) with large effects on bristle number were mapped cytogenetically. Two P-element-induced scabrous alleles and five extramacrochaetae alleles were generated. Single P-element mutagenesis is a powerful method for identifying QTLs at the level of genetic locus.     

Effects of tracking devices on individual birds – a review of the evidence

We review long‐term patterns of tracking device use and the reporting of the effects of such devices on individual birds. We assessed > 3400 primary references including > 1500 containing information as to whether effects were looked for and reported. Numbers of papers published increased at 4.4% yr^–1. Research on foraging and energetics focussed on seabirds while work on habitat use and dispersal was focussed mainly on landbirds. Migration was the most common study topic overall and increased markedly from the turn of the century in all three bird groups. The proportion of studies reporting effects of devices on individuals declined at > 1% yr^–1, while the proportion of studies providing no information on effects increased by ca 0.7% yr^–1. The presence of a control group increased the likelihood of a study reporting effects, (45 vs 33%). We modelled the probability of reporting effects separately for three bird groups and two attachment durations. Occurrence of effects was significantly related to attachment method (4 models), year (4 models) and relative device mass (1 model). Invasive attachment methods were associated with a high incidence of effects while tail and leg attachments showed relatively few effects. Probabilities of reporting effects declined over time and increased with relative device mass, however there was no device mass threshold below which effects were not observed. Approaches designed to minimize potential effects of devices on individual birds and to improve scientific rigour have advanced substantially. Nevertheless ca 55% of studies contained no information on potential effects and in many more documentation was inadequate. We call for more systematic documentation of potential effects in peer‐reviewed publications to support more rigorous science and to further improve bird welfare.     

Scale and system dependencies of indirect effects of large herbivores on phytophagous insects: a meta-analysis

An increasing number of studies are being conducted to examine the density- or trait-mediated indirect effects of large herbivores on phytophagous insects. However, these effects are highly context dependent and no general trends have been made clear. We conducted a meta-analysis focusing on three factors capable of affecting detection of the indirect effects of large herbivores on phytophagous insects: type of response variable, experimental scale, and characteristics of study organisms. Overall, large herbivores exerted a negative effect on insects, a trend that was prominent in studies using insect abundance as a response variable. No particular trends were observed in studies using herbivory rate as a variable, and these studies often focused on plant trait-mediated effects more than density-mediated ones. Experimental scale affected the strength of indirect effects: within-year or individual tree level experiments did not follow any trends, whereas 1–10 year experiments or 0–10 ha scale experiments show a negative impact on insects. Characteristics of large herbivores and growth forms of transmitter plants also contributed to variations in the observed effect size; negative effects were reported in livestock-grassland ecosystems and neutral effects in tree-dominated systems. There was a close association between response variable, experimental scale, and characteristics of study organisms, and these effects jointly contributed to the apparent trends. To predict the impacts of large herbivores at ecosystem level, it is necessary to eliminate these biases arising from study design and to evaluate the effect on insect densities at large spatial and temporal scales.     

The Evolution of Multivariate Maternal Effects

There is a growing interest in predicting the social and ecological contexts that favor the evolution of maternal effects. Most predictions focus, however, on maternal effects that affect only a single character, whereas the evolution of maternal effects is poorly understood in the presence of suites of interacting traits. To overcome this, we simulate the evolution of multivariate maternal effects (captured by the matrix M) in a fluctuating environment. We find that the rate of environmental fluctuations has a substantial effect on the properties of M: in slowly changing environments, offspring are selected to have a multivariate phenotype roughly similar to the maternal phenotype, so that M is characterized by positive dominant eigenvalues; by contrast, rapidly changing environments favor Ms with dominant eigenvalues that are negative, as offspring favor a phenotype which substantially differs from the maternal phenotype. Moreover, when fluctuating selection on one maternal character is temporally delayed relative to selection on other traits, we find a striking pattern of cross-trait maternal effects in which maternal characters influence not only the same character in offspring, but also other offspring characters. Additionally, when selection on one character contains more stochastic noise relative to selection on other traits, large cross-trait maternal effects evolve from those maternal traits that experience the smallest amounts of noise. The presence of these cross-trait maternal effects shows that individual maternal effects cannot be studied in isolation, and that their study in a multivariate context may provide important insights about the nature of past selection. Our results call for more studies that measure multivariate maternal effects in wild populations.     

Structure-activity relationships of 18 endogenous neuropeptides on the motor nervous system of the nematode Ascaris suum

Neuropeptides play an important role in all nervous systems and structure-activity studies of related peptides is one approach to understanding this role. This study of the motor nervous system of the parasitic nematode Ascaris suum describes the physiological effects of a family of 18 endogenous Ascaris FMRFamide-like peptides (AF peptides) on the membrane potential and input resistance of the dorsal excitatory type 2 (DE2) and dorsal inhibitory (DI) motor neurons. These motor neurons are part of the final common output pathway from the motor nervous system to the somatic muscle cells responsible for locomotion. AF peptide effects on the frequency of excitatory postsynaptic potentials (EPSPs) in DE2 motor neurons were also measured to infer peptide effects on central presynaptic spiking neurons. AF peptide injections into intact worms were made to assess their qualitative effects on behavior, providing a context for interpreting motor neuron data. One category of AF peptides, N-terminally extended -FIRFa peptides (AF5, AF7 and AF1), has pronounced behavioral effects and qualitatively similar, but quantitatively different effects on DE2 and DI motor neurons. A second category of AF peptides (AF2, AF9, and AF8) also produces dramatic behavioral effects and strong electrophysiological effects on DE2 and/or DI motor neurons. A third category of AF peptides, consisting of six members of the -PGVLRFa group (which are encoded by the same gene and have closely related sequences) and peptide AF11, have pronounced behavioral effects, but relatively weak or negligible effects on DE2 and DI motor neurons. A fourth category of AF peptides, also consisting of structurally unrelated members, has pronounced behavioral effects and, as individual peptides, similar effects on both DE2 and DI motor neurons; AF15 is excitatory, while AF17 and AF19 are inhibitory, on both motor neuron types. Finally, two AF peptides (AF6, AF16) are relatively weak or inactive in producing behavioral or motor neuronal effects. Based on comparisons of the effects of AF peptides on DE2 and DI motor neurons, a tentative list of 5 major response-types is proposed as a working hypothesis to guide the search for AF peptide receptors. The findings attest to the potential complexity of neurosignaling in this comparatively simple nervous system.     

Positive Effects of Plant Genotypic and Species Diversity on Anti-Herbivore Defenses in a Tropical Tree Species

Despite increasing evidence that plant intra- and inter-specific diversity increases primary productivity, and that such effect may in turn cascade up to influence herbivores, there is little information about plant diversity effects on plant anti-herbivore defenses, the relative importance of different sources of plant diversity, and the mechanisms for such effects. For example, increased plant growth at high diversity may lead to reduced investment in defenses via growth-defense trade-offs. Alternatively, positive effects of plant diversity on plant growth may lead to increased herbivore abundance which in turn leads to a greater investment in plant defenses. The magnitude of trait variation underlying diversity effects is usually greater among species than among genotypes within a given species, so plant species diversity effects on resource use by producers as well as on higher trophic levels should be stronger than genotypic diversity effects. Here we compared the relative importance of plant genotypic and species diversity on anti-herbivore defenses and whether such effects are mediated indirectly via diversity effects on plant growth and/or herbivore damage. To this end, we performed a large-scale field experiment where we manipulated genotypic diversity of big-leaf mahogany (Swietenia macrophylla) and tree species diversity, and measured effects on mahogany growth, damage by the stem-boring specialist caterpillar Hypsipyla grandella, and defensive traits (polyphenolics and condensed tannins in stem and leaves). We found that both forms of plant diversity had positive effects on stem (but not leaf) defenses. However, neither source of diversity influenced mahogany growth, and diversity effects on defenses were not mediated by either growth-defense trade-offs or changes in stem-borer damage. Although the mechanism(s) of diversity effects on plant defenses are yet to be determined, our study is one of the few to test for and show producer diversity effects on plant chemical defenses.     

Quantitative interpretations of double mutations of enzymes.

The quantitative effect of a second mutation on a mutant enzyme may be antagonistic, absent, partially additive, additive, or synergistic with respect to the first mutation. Depending on which kinetic or thermodynamic parameter of an enzyme is measured, the same two mutations can interact differently in the double mutant. Additive effects of two mutations on an equilibrium constant, such as the dissociation constant of the enzyme-substrate complex (KS), occur when noninteracting residues which facilitate the same step (substrate binding) are mutated. Partially additive effects result from the cooperative interaction with the substrate of the two residues mutated, and synergistic effects result from the anticooperative interaction with the substrate of the two residues mutated. An alternative explanation for synergy is extensive unfolding of the enzyme. Antagonistic effects on an equilibrium constant such as KS result from opposing structural effects of the two mutations on substrate binding. No additional effect of the second mutation in the double mutant represents a limiting case of either partial additivity or antagonism [corrected]. The interactions of the effects of two mutations on a rate constant such as kcat have the same explanations as those given above for equilibrium constants since the binding of a rate-limiting transition state is occurring. However, due to kinetic complexity, the following exceptions and additions exist. Additive effects of two mutations on kcat occur when noninteracting residues which facilitate the same step are mutated, provided this step is rate limiting. If the affected step is not rate limiting then synergistic effects of the two mutations are observed as each mutation causes the step to become progressively more rate limiting. Additive effects on kcat also occur when the two mutations affect consecutive steps, provided one of them is rate limiting. Partially additive effects on kcat also occur when noninteracting residues facilitating consecutive, non-rate-limiting steps are mutated. These concepts, when applied to published data on double mutants of delta 5-3-ketosteroid isomerase, staphylococcal nuclease, tyrosyl-tRNA synthetase, glutathione reductase, and subtilisin, provide deeper insights into the independent, cooperative, anticooperative, or antagonistic interactions of amino acid residues in the binding of substrates, activators, and inhibitors and in promoting catalysis.     

Large manipulative experiments reveal complex effects of food supplementation on population dynamics of Brandt's voles

Although food supplementation is well known to increase population density,there is still debate on the causative effects of food supplementation on reproduction,survival,and immigration.Large manipulative experiments,which exclude any confounding effects of dispersal and predation,are essential for clarifying the debate.In this study,we investigated the effects of food supplementation on Brandt's vole population dynamics and plant community in eight large enclosures(0.48 ha each) from2010 to 2014.Food supplementation showed significant positive effects on population density due to increases in recruitment;however,it showed a complex effect on survival of voles:positive in non-breeding seasons,but negative in breeding seasons.In addition,food supplementation increased the quality of plants(as reflected by increased crude protein content),but decreased the quantity of less preferred plants in experimental enclosures.Thus,food seems to have direct positive effects on small rodents through improvement of food supply and indirect negative effects through food-induced density-dependent effects,and may have long-term effects on rodents through altering plant community composition and abundance.     

Randomization of Neighbour Balanced Designs

This paper is a simulation study on the influence of interference between treatments in field trials. The considerations in the paper are based on a simple model which includes additive neighbour effects of treatments. We use uniformity data where neighbour effects are added, to demonstrate the influence that these effects have on the validity of comparisons between treatments. The simulations illustrate that the influence of the neighbour effects is reduced if a neighbour balanced or a partially neighbour balanced design is used.     

Effects of alpha-tocopherol (vitamin E) on the stability and lipid dynamics of model membranes mimicking the lipid composition of plant chloroplast membranes

Tocopherol (vitamin E) is widely recognized as a cellular antioxidant. It is essential for human and animal health, but only synthesized in photosynthetic organisms, where it is localized in chloroplast membranes. While many studies have investigated non-antioxidative effects of tocopherol on phospholipid membranes, nothing is known about its effects on membranes containing chloroplast glycolipids. Here, liposomes resembling plant chloroplast membranes were used to investigate the effects of alpha-tocopherol on vesicle stability during freezing and on lipid dynamics. alpha-Tocopherol had a pronounced influence on membrane dynamics and showed strong interactions in its effects on membrane stability during freezing with the cryoprotectant sucrose. alpha-Tocopherol showed maximal effects at low concentrations (around 2mol%), close to its contents in chloroplast membranes.     

Additive effects of functionally dissimilar above- and belowground organisms on a grassland plant community

Aims In nature, plant communities are affected simultaneously by a variety of functionally dissimilar organisms both above and below the ground. However, there is a gap of knowledge on interactive effects of functionally dissimilar organisms on plant communities that is needed to be filled to better understand and predict the general impact of biotic factors on plant communities.Methods We conducted a full-factorial mesocosm study to investigate the individual and combined impacts of above- and belowground functionally dissimilar organisms on a grassland plant community. We studied the effects of aboveground herbivores (Helix aspersa, Gastropoda), arbuscular mycorrhizal fungi (AMF; Glomus spp., Glomeromycota) and endogeic earthworms (Aporrectodea spp., Lumbricidae) on the diversity, structure and productivity of an experimental grassland plant community and each other.Important findings Aboveground herbivory by snails decreased, AMF increased and earthworms had no effects on the diversity of the grassland plant community, while their combined effects were additive. The biomass of the plant community was negatively affected by snails and AMF, while no effects of earthworms or interaction effects were found. The plant species were differently affected by snails and AMF. No effects of the above- and belowground organisms on each other's performance were detected. Since the effects of the functionally dissimilar organisms on the grassland plant community were mainly independent, the results indicate that their combined effects may be predicted by knowing the individual effects, at least under the conditions used in the present mesocosm study.     

Effects of adenosine perfusion on the metabolism and contractile activity of Rana ridibunda heart

The effects of adenosine were examined on the isolated perfused heart of the frog Rana ridibunda. Adenosine produced negative chronotropic and inotropic effects on frog ventricle in a concentration-dependent manner. The effects of adenosine on cardiac metabolism were also investigated by measuring the tissue content of adenine nucleotides, lactate, pyruvate, adenosine and inorganic phosphate, during adenosine perfusion. Adenosine had no effect on the tissue content of metabolites. No net synthesis of adenine nucleotides was observed during perfusion with increasing concentrations of adenosine. Lactate output from the heart decreased significantly with adenosine perfusion. Correlation of adenosine effects on cardiac muscle with the effects of hypoxia are discussed.     

Nicotine self-medication of cognitive-attentional processing

This article selectively reviews research concerning nicotine's effects on cognition, including the neurobiological mechanism for these effects, task and experimental features that may be important for elucidating these effects, and why these effects may have amplified motivational significance among smokers with cognitive deficit. Nicotine has effects on various cognitive processes, though most studies in humans have focused on the amelioration of cognitive deficits experienced during drug withdrawal. The direct cognitive-enhancing effect of nicotine remains a controversial topic. The relationship between attentional and non-attentional cognitive effects of nicotine is discussed in the context of cognitive self-medication. Further research should include theory-driven examination of cognitive effects of nicotine, and develop targeted smoking cessation programs based on an improved understanding of the role of cognitive self-medication in high-risk individuals.     

Effects of Radio-Collars are not Contingent on Socioecological Conditions in Degus

Species-specific research on free-ranging mammals reveals a diversity of effects of radio-collars on behavior, body condition, and fitness. Although these studies indicate rather limited direct effects, radio-collars may cause effects influenced by socio-ecological conditions. Using a 7-year study on a natural population of group-living degus (Octodon degus), we tested the hypothesis that ecological (food availability, burrow density) and social (group size, group male-to-female ratio) conditions modulate effects of radio-collars on body condition (e.g., body mass, ecto- and endoparasite loads, fecal cortisol metabolites) and direct fitness (litter size, adult survival). We determined the effect of radio-collar use on degus by contrasting the presence or absence of radio-collars, quantifying the effects of the number of days carrying a radio-collar, and the relative mass of radio-collars worn by degus in central Chile between 2009 and 2015. Radio-collar use was not associated with direct effects on litter size, adult survival, or with body mass and fecal cortisol metabolites but was linked to low ecto- and endoparasite loads. These seemingly positive effects may reflect decreased mobility, or a research bias for radio-collaring larger, healthier individuals. There was no evidence that ecological and social conditions modulated radio-collar effects on degu body condition and direct fitness. These findings are consistent with evidence from other mammal studies that reported no appreciable detrimental direct or indirect effects of radio-collars. © 2021 The Wildlife Society.     

Fitness consequences of maternal and grandmaternal effects

Transgenerational effects are broader than only parental relationships. Despite mounting evidence that multigenerational effects alter phenotypic and life‐history traits, our understanding of how they combine to determine fitness is not well developed because of the added complexity necessary to study them. Here, we derive a quantitative genetic model of adaptation to an extraordinary new environment by an additive genetic component, phenotypic plasticity, maternal and grandmaternal effects. We show how, at equilibrium, negative maternal and negative grandmaternal effects maximize expected population mean fitness. We define negative transgenerational effects as those that have a negative effect on trait expression in the subsequent generation, that is, they slow, or potentially reverse, the expected evolutionary dynamic. When maternal effects are positive, negative grandmaternal effects are preferred. As expected under Mendelian inheritance, the grandmaternal effects have a lower impact on fitness than the maternal effects, but this dual inheritance model predicts a more complex relationship between maternal and grandmaternal effects to constrain phenotypic variance and so maximize expected population mean fitness in the offspring.     

Effects of environmental stressors on stem cells

Environmental toxicants are ubiquitous,and many are known to cause harmful health effects.However,much of what we know or think we know concerning the targets and long-term effects of exposure to environmental stressors is sadly lacking.Toxicant exposure may have health effects that are currently mischaracterized or at least mechanistically incompletely understood.While much of the recent excitement about stem cells(SCs)focuses on their potential as therapeutic agents,they also offer a valuable resource to give us insight into the mechanisms and risks of toxicant effects.Not only as a response to the increasing ethical pressure to reduce animal testing,SC studies allow us valuable insight into the true effects of human exposure to environmental stressors under controlled conditions.We present a review of the history of publications on the effects of environmental stressors on SCs,followed by a consolidation of the literature over the past five years on a subset of key environmental stressors of importance to human health and their effects on both embryonic and tissue SCs.The review will make constructive suggestions as to areas of toxicant research where further studies are needed,as well as making indications of the potential utility for advancing knowledge and directing research on environmental toxicology.     

A review of the role of fire in nutrient cycling in Australian native forests,and of methodology for studying the fire-nutrient interaction*

Previous studies relating to the effects of fire on nutrient cycling in Australian native forests are reviewed. It is apparent that: (a) the action of fire on soil fertility is likely to be important in affecting the functioning of Australian plant communities, (b) work to date only gives a guide as to the nature and magnitude of the effects of fire on some nutrient pools and nutrient cycling processes, but has not established the significance of such effects to the nutrient budget of entire forest systems, or established the links between fire, soil fertility and the functioning of forest communities. The difficulties associated with studying and predicting the long-term effects of fire on the fertility of forest soils are discussed. A new methodology applicable to study of the interaction between fire and plant nutrition is advocated, and is based on examination of the effects of fire on nutrient stores and flux rates in the soil-litter compartment of the forest. This approach emphasizes the use of changes in rates of nutrient cycling processes as an index of the-effects of disturbances such as fire on a forest ecosystem. The application of the methodology in a study of the effects of repeated low-intensity prescribed burning on soil fertility is discussed briefly.