Modeling the effects of enclosure size on geometry learning

Several recent studies have shown that chickens, fish, and humans trained to find a reward in a corner of a rectangular enclosure with distinctive features rely more on the geometry of the enclosure in small enclosures and rely more on the features in large enclosures. Here, these results are modeled using a recent associative model of geometry learning [Miller, N.Y., Shettleworth, S.J., 2007. Learning about environmental geometry: an associative model. J. Exp. Psychol. Anim. B 33, 191–212]. By adjusting the salience of either geometric or featural information or both the model is capable of reproducing much of the data on the effects of enclosure size on geometry learning.     

Modeling the effects of musculoskeletal geometry on scapulohumeral muscle moment arms and lines of action

Abstract

Biomechanical investigations examining shoulder function commonly observe a high degree of inter-individual variability in muscle activity and kinematic patterns during static and dynamic upper extremity exertions. Substantial differences in musculoskeletal geometry between individuals can alter muscle moment arms and lines of action that, theoretically, alter muscle activity and shoulder kinematics. The purposes of this research were to: (i) quantify model-predicted functional roles (moment arms, lines of action) of the scapulohumeral muscles, (ii) compare model predictions to experimental data in the literature, and (iii) evaluate sensitivity of muscle functional roles due to changes in muscle attachment locations using probabilistic modeling. Monte Carlo simulations were performed to iteratively adjust muscle attachment locations at the clavicle, scapula, and humerus of the Delft Shoulder and Elbow Model in OpenSim. Muscle moment arms and lines of action were quantified throughout arm elevation in the scapular plane. In general, model-predicted moment arms agreed well with the reviewed literature; however, notable inconsistencies were observed when comparing lines of action. Variability in moment arms and lines of action were muscle-specific, with 2 standard deviations in moment arm and line of actions as high as 25.8?mm and 18.8° for some muscles, respectively. Moment arms were particularly sensitive to changes in attachment site closest to the joint centre. Variations in muscle functional roles due to differences in musculoskeletal geometry are expected to require different muscle activity and movement patterns for upper extremity exertions.     

Temperature and water content effects on the viscoelastic behavior of<Emphasis Type="Italic"> Tilia americana</Emphasis> (Tiliaceae) sapwood

The effects of temperature and water content on the viscoelasticity of living and dehydrated Tilia americana sapwood were examined using transient creep (time- and load-dependent deformation) tests under sustained bending loads. Creep tests were performed at 21.1°C and –20.5°C to determine the magnitudes and types of strains in living and dehydrated samples. Temperature had no effect on the creep rate of living sapwood. However, the creep rate of dehydrated samples at –20.5°C was significantly faster than that at 21.1°C. Regardless of temperature, sapwood had a faster creep rate than dehydrated samples. With small bending loads, the residual strains in sapwood were larger at 21.1°C compared to –20.5°C. Temperature did not significantly affect the residual strains in dehydrated samples. For small bending loads, frozen sapwood recovered all residual creep strains when thawed. With larger loads, residual and plastic (permanent) strains increased. We speculate that ice formation in cell lumens partially dehydrates (and thus stiffens and strengthens) cell wall materials and prevents cell wall buckling and elastic restoration after unloading. However, when thawed, sapwood can elastically restore its original configuration, provided it is not excessively bent (by ice or snow accumulations) when frozen.     

Comparing the effects of rapid evolution and phenotypic plasticity on predator-prey dynamics

Ecologists have increasingly focused on how rapid adaptive trait changes can affect population dynamics. Rapid adaptation can result from either rapid evolution or phenotypic plasticity, but their effects on population dynamics are seldom compared directly. Here we examine theoretically the effects of rapid evolution and phenotypic plasticity of antipredatory defense on predator-prey dynamics. Our analyses reveal that phenotypic plasticity tends to stabilize population dynamics more strongly than rapid evolution. It is therefore important to know the mechanism by which phenotypic variation is generated for predicting the dynamics of rapidly adapting populations. We next examine an advantage of a phenotypically plastic prey genotype over the polymorphism of specialist prey genotypes. Numerical analyses reveal that the plastic genotype, if there is a small cost for maintaining it, cannot coexist with the pairs of specialist counterparts unless the system has a limit cycle. Furthermore, for the plastic genotype to replace specialist genotypes, a forced environmental fluctuation is critical in a broad parameter range. When these results are combined, the plastic genotype enjoys an advantage with population oscillations, but plasticity tends to lose its advantage by stabilizing the oscillations. This dilemma leads to an interesting intermittent limit cycle with the changing frequency of phenotypic plasticity.     

Developmental plasticity and maternal effects of reproductive characteristics in the frog,Bombina orientalis

Summary Life history theory suggests that reproductive characteristics such as ovum size and clutch size should be well buffered against vararies of the environment. However, studies which demonstrate environmental sensitivity of reproductive characteristics are increasing in number, as are studies which find that maternal effects are responsible for much of the variation in developmental and growth rates in embryonic and larval fish and amphibians. The data reported here demonstrate that the environment, in terms of temperature and food availability that a specific individual encounters during vitellogenesis, exerts a strong influence on both egg size and number. Warmer temperatures and less food decrease ovum size, while colder temperatures and less food decrease clutch size. The variation in ovum size that is induced by the environment can exert a strong influence on variation in offspring development and growth and serve as an excellent model for studies on the evolution of developmental plasticity.     

Genetic Allee effects on performance, plasticity and developmental stability in a clonal plant

Negative effects of small population size on fitness, so-called Allee effects, may threaten population persistence even in intact habitat remnants. We studied genotypes of 14 isolated populations of the clonal plant Ranunculus reptans, for which molecular genetic (RAPD-) variability is higher for large than for small populations. In a competition-free greenhouse environment vegetative offspring of genotypes from large populations produced more rosettes and flowers, indicating higher fitness. Within-genotype coefficients of variation in performance traits, indicating developmental instability, were lower for genotypes from populations with higher RAPD-variability. In competition with a taller grass, we found relative reduction in leaf length less pronounced for plants from large populations, suggesting higher adaptive plasticity. Our experimental study of a plant with predominantly vegetative reproduction suggests, that negative genetic effects of recent habitat fragmentation, which so far rather were expected in plants with frequent sexual reproduction, are more severe and more common than previously acknowledged.     

Modifying effects of phenotypic plasticity on interactions among natural selection, adaptation and gene flow

Divergent natural selection, adaptive divergence and gene flow may interact in a number of ways. Recent studies have focused on the balance between selection and gene flow in natural populations, and empirical work has shown that gene flow can constrain adaptive divergence, and that divergent selection can constrain gene flow. A caveat is that phenotypic diversification may be under the direct influence of environmental factors (i.e. it may be due to phenotypic plasticity), in addition to partial genetic influence. In this case, phenotypic divergence may occur between populations despite high gene flow that imposes a constraint on genetic divergence. Plasticity may dampen the effects of natural selection by allowing individuals to rapidly adapt phenotypically to new conditions, thus slowing adaptive genetic divergence. On the other hand, plasticity may promote future adaptive divergence by allowing populations to persist in novel environments. Plasticity may promote gene flow between selective regimes by allowing dispersers to adapt to alternate conditions, or high gene flow may result in the selection for increased plasticity. Here I expand frameworks for understanding relationships among selection, adaptation and gene flow to include the effects of phenotypic plasticity in natural populations, and highlight its importance in evolutionary diversification.     

Age-dependent effects of chronic stress on brain plasticity and depressive behavior

Exposure to chronic mild stress (CMS) is known to induce anhedonia in adult animals, and is associated with induction of depression in humans. However, the behavioral effects of CMS in young animals have not yet been characterized, and little is known about the long-term neurochemical effects of CMS in either young or adult animals. Here, we found that CMS induces anhedonia in adult but not in young animals, as measured by a set of behavioral paradigms. Furthermore, while CMS decreased neurogenesis and levels of brain-derived neurotrophic factor (BDNF) in the hippocampus of adult animals, it increased these parameters in young animals. We also found that CMS altered alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptor GluR1 subunit levels in the hippocampus and the nucleus accumbens of adult, but not young animals. Finally, no significant differences were observed between the effects of CMS on circadian corticosterone levels in the different age groups. The substantially different neurochemical effects chronic stress exerts in young and adult animals may explain the behavioral resilience to such stress young animals possess.     

Inhibitory effects of caffeine on gustatory plasticity in the nematode Caenorhabditis elegans

The effects of caffeine on salt chemotaxis learning were investigated using the nematode Caenorhabditis elegans. To estimate the degree of salt chemotaxis learning, nematodes were placed in a mixed solution of NaCl and caffeine, and then the chemotaxis index of NaCl was obtained from the nematodes placed on agar medium after pre-exposure to caffeine concentrations of 0.01, 0.1, 0.3, and 1.0%. Locomotor activity and preference behavior for caffeine were also estimated under these caffeine conditions. Nematodes pre-exposed to 0.3% caffeine showed inhibition of salt chemotaxis learning. Additional experiments indicated that nematodes showed a preference response to the middle concentration of caffeine (0.1%), with preference behavior declining in the 0.3% caffeine condition. Stable locomotor activity was observed under 0.01–0.3% caffeine conditions. These results suggest that salt chemotaxis learning with 0.3% caffeine is useful for investigating the effects of caffeine on learning in nematodes.     

Anion- and pH-linked effects on the heme-iron geometry in ferrous nitrosylated monomeric myoglobins

 The cooperative effect of anions and proton concentration on the EPR spectroscopic properties of the ferrous nitrosylated derivative of monomeric Mb from loggerhead sea turtle (Caretta caretta), sperm whale (Physeter catodon), and horse (Caballus caballus) has been investigated between pH 4.5 and 9.0, at 100 K. In the absence of anions, an EPR spectrum characteristic of the hexa-coordinated species of ferrous nitrosylated Mb with an axial geometry is observed, which is unaffected by pH. On the other hand, a transition toward a species characterized by an EPR spectrum corresponding to a hexa-coordinated rhombic geometry takes place in the presence of phosphate, acetate, citrate, sulfate, and chloride. Only the hexa-coordinated form characterized by the rhombic EPR spectrum appears then to undergo a pH-dependent transition toward the penta-coordinated species. Present results show clear-cut evidence for the spectroscopic coupling of proton and anion binding sites with the Mb reactive center, indicating that an allosteric mechanism might modulate the proximal HisF8-heme-NO geometry in monomeric hemoproteins. Received: 15 December 1997 / Accepted: 15 June 1998     

Collagen fiber orientation and geometry effects on the mechanical properties of secondary osteons.

The effects of collagen fiber orientation and osteon geometry on the mechanical properties of secondary osteons under axial compression/tension and combined loadings (compression, bending and torsion) were investigated using a composite-beam finite-element model. Three cross-sectional shapes of secondary osteons were studied to show the effect of geometry. The results of stiffness are presented using the tension and compression properties for each lamella. The model shows that the mechanical properties of osteons are enhanced in bending and torsion when collagen fibers are oriented within 30 degrees of the loading axis. Osteons with alternating lamellar orientation are not well adapted to resist torsional moments, but alternate collagen fiber orientation has virtually no effect on the bending stiffness of osteons. Fiber orientation affects the mechanical properties less significantly when osteons are non-circular. Collagen fiber orientation and osteon geometry interact to determine the mechanical behavior of the osteon, and may act in a compensatory manner in the adaptive process.     

The effects of various soils,different provenances and air pollution on root tip chromosomes in Norway spruce

The classification of chromosomal aberrations was used to characterize different factors affecting chromosomes in the root meristem of Norway spruce [Picea abies (L.) Karst.] trees. It is important to know the most significant factor affecting the chromosomes in the root meristem of plants at natural sites. The results suggest that an intensive site effect is more significant than the soil or the provenance of the individual. This cytogenetic plant test system was also used to investigate 5-year-old spruce trees exposed in environmental chambers to elevated concentrations of carbon dioxide (750 cm³m^–3) and ozone (0.08 cm³m^–3) as single variables or in combination, and then transferred to a field for observation of a memory effect. The fumigated variants showed an increased number of chromosomal aberrations compared to the controls, which carried on as a memory effect in the root meristems far beyond the fumigation period.     

Soil-derived organic particles and their effects on the community of culturable microorganisms

Soil microbial community interacts with a range of particulate material in the soil, consisting of both inorganic and organic compounds with different levels of water solubility. Though sparingly water-soluble and insoluble organic compounds in the soil may affect living organisms, they are difficult to introduce into microbiological media. Their biological activity (i.e., their effect on soil microorganisms) thus has been almost neglected in most of the cultivation assays. To fill this gap, we propose the use of fine organic particles prepared from soil organic matter that are introduced into a laboratory medium where microbial community is cultivated. To this purpose, submicrometer particles consisting of sparingly water-soluble or insoluble soil organic matter were obtained from humic horizons of two soils by precipitation of organics dissolved in tetrahydrofuran by addition of water. The particles could then be size fractionated by centrifugation, and coarse fraction obtained from humic horizon formed under spruce forest was tested for effects on complex microbial community developing under laboratory conditions. The results indicate that low concentration (20 mg/L) of the particles is efficient to affect the composition of the bacterial community revealed by terminal restriction fragment length polymorphism. The work contributes to understanding the factors that determine the composition of soil microbial community.     

Theoretical study on the effects of pressure-induced remodeling on geometry and mechanical non-homogeneity of conduit arteries

A structure-based mathematical model for the remodeling of arteries in response to sustained hypertension is proposed. The model is based on the concepts of volumetric growth and constitutive modeling of the arterial tissue within the framework of the constrained mixture theory. The major novel result of this study is that remodeling is associated with a local change in the mass fractions of the wall constituents that ultimately leads to mechanical non-homogeneity of the arterial wall. In the new homeostatic state that develops after a sustained increase in arterial pressure, the mass fraction of elastin decreases from the intimal side to the adventitial side of arteries, while the collagen fraction manifests an opposite trend. The results obtained are supported by some experimental observations reported in the literature.     

机械刺激对匍匐茎型植物蛇莓(Duchesnea indica)克隆可塑性的影响（英文）

机械刺激(mechanical stimuli, MS)在自然界的分布较为普遍,然而关于机械刺激对匍匐茎型克隆植物影响的研究相对较少。为此,实验对匍匐茎型克隆植物蛇莓(Duchesneaindica)进行了对照(无机械刺激)、克隆片段顶部刺激、半克隆片段刺激和整克隆片段刺激共四个水平的机械刺激处理,通过研究蛇莓克隆生长的响应,探讨机械刺激对其作用机理。结果表明:与对照相比,机械刺激导致蛇莓产生较多的分株、较多的匍匐茎、短而细的叶柄及较多的根生物量分配。同时,不同作用位点的机械刺激对各生理生长指标的效应差异并不显著。另外,通过对各生长指标表型可塑性指数的分析发现,分株数具有较高的可塑性指数。上述实验结果表明,蛇莓可以较好地适应机械刺激干扰的生境,其分株数可以作为其响应程度的较好的指示指标。     

Anti-androgenic effects of bisphenol-A on spatial memory and synaptic plasticity of the hippocampus in mice

Bisphenol-A (BPA) is a common environmental endocrine disruptor. Our recent studies found that exposure to BPA in both adolescent and adulthood sex-specifically impaired spatial memory in male mice. In this study, 11-week-old gonadectomied (GDX) male mice daily received subcutaneous injections of testosterone propionate (TP, 0.5 mg/kg), TP and BPA (0.4 and 4 mg/kg), or vehicle for 45 days. The results of Morris water maze task showed that exposure to BPA did not affect the spatial memory of GDX mice but impaired that of sham (4 mg/kg/day) and TP-treated GDX mice (0.4 mg/kg/day). In addition, BPA reduced the level of testosterone (T) in the serum and brain of sham and TP-treated GDX mice. Exposure to BPA decreased the synaptic density and had an adverse effect on the synaptic interface of the hippocampus in sham and TP-treated GDX mice. The results of western blot analysis further showed that BPA (4 mg/kg) reduced the levels of synaptic proteins (synapsin I and PSD-95) and NMDA receptor subunit NR2B in sham and TP-treated GDX mice. BPA decreased the phosphorylation of ERK1/2 but increased the phosphorylation of p38 in sham and TP-treated GDX mice. These results suggest that impairment of spatial memory and adverse effects on synaptic remodeling of hippocampal neurons in males after long-term BPA exposure is related to the anti-androgen effect of BPA. These effects of BPA may be associated with downregulated synaptic proteins and NMDA receptor through inhibiting ERKs and promoting the p38 pathways.     

Antipodal effects of p25 on synaptic plasticity, learning, and memory--too much of a good thing is bad

Elevated activity of the Cdk5/p25 complex has been implicated in the pathogenesis of Alzheimer's disease. The report by Fischer and colleagues in this issue of Neuron describes a dichotomous role for the activator protein p25 in synaptic plasticity, learning, and memory, whereby transient expression in transgenic mice produces beneficial effects, but prolonged expression is detrimental. This work demonstrates the complexity of Cdk5/p25 in neuronal function and shows that dysregulation of a factor involved in plasticity can cause neurodegeneration.