Current Patch Research Articles

Modelling dispersal with diffusion and habitat selection: Analytical results for highly fragmented landscapes

Quantifying dispersal is crucial both for understanding ecological population dynamics, and for gaining insight into factors that affect the genetic structure of populations. The role of dispersal becomes pronounced in highly fragmented landscapes inhabited by spatially structured populations. We consider a landscape consisting of a set of habitat patches surrounded by unsuitable matrix, and model dispersal by assuming that the individuals follow a random walk with parameters that may be specific to the habitat type. We allow for spatial variation in patch quality, and account for edge-mediated behavior, the latter meaning that the individuals bias their movement towards the patches when close to an edge between a patch and the matrix. We employ a diffusion approximation of the random walk model to derive analytical expressions for various characteristics of the dispersal process. For example, we derive formulae for the time that an individual is expected to spend in its current patch i, and for the time that it will spend in the matrix, both conditional on the individual hitting next a given patch j before hitting any of the other patches or dying. The analytical formulae are based on the assumptions that the landscape is infinitely large, that the patches are circularly shaped, and that the patches are small compared to interpatch distances. We evaluate the effect of these assumptions by comparing the analytical results to numerical results in a real patch network that violates all of the three assumptions. We then consider a landscape that fulfills the assumptions, and show that in this case the analytical results are in a very good agreement with the numerical results. The results obtained here allow the construction of computationally efficient dispersal models that can be used as components of metapopulation models.

Small fiber neuropathy associated with multiple myeloma and IgA monoclonal gammopathy

Dear Editor,Monoclonal gammopathy (MG) is frequent in patients withperipheral neuropathy of otherwise undetermined etiology[1]. Clinically, MG-associated neuropathy usually manifestsas a slowly progressive sensorimotor polyneuropathy withnumbness and ataxia, with rare involvement of small nervefibers [1–4].Case reportA 33-year-old Caucasian woman with stage IA multiplemyeloma [5] presented with a 4-year history of painfulneuropathy. She was diagnosed with myeloma 18 months agoand treated with thalidomide and later fludarabine at anoutside hospital. Neuropathic pain continued to worsen afterchemotherapy and was described as a severe deep achegraded 10/10 that worsened with activity, restricting her to theuse of a motorized wheelchair. Laboratory testing showedmonoclonal IgA λ protein at 1.91 g/dl, with elevated freelight chains in the serum at 84.9 mg/l (normal 5.7 –26.3 mg/l).There were no skin or endocrine abnormalities. Bone marrowbiopsy and fat pad biopsy were negative for amyloid, butshowed 20% myeloma cell infiltration rate in the marrow.There was no history of diabetes. Current medicationsincluded transdermal fentanyl patch, pregabalin, sertraline,and hydrocodone. Examination showed normal sensation tovibration and proprioception, with mildly decreased sensationto pinprick and cold temperature below ankles. Cranialnerves, muscle strength, deep tendon reflexes, proprioception,and coordination were normal. Nerve conduction studies andelectromyography were normal. Semithin plastic and paraffinsections of sural nerve biopsy were suggestive of small nervefiber dropout, without evidence of inflammation or amyloid-osis. Quantitative sensory testing (QST) using CASE IV (WRElectronics, Stillwater, MN, USA) showed decreasedsensory thresholds to vibration (>95th percentile in the leftfoot and >99th percentile in the left hand and right foot;normal 99th percentile inboth feet and the left hand). Neuropathic symptoms did notimprove after plasmapheresis. Subsequent MRI of the spineshowed diffusely abnormal bone marrow signal in cervical,thoracic, and lumbar regions, and serum electrophoresisshowed rise of β-2-microglobulin. Subsequently, patientunderwent chemotherapy with cyclophosphamide and mel-phalan, followed by autologous peripheral blood stem celltransplantation. At 1 year after transplantation, there wasno significant change in her neuropathic pain.DiscussionSmall fiber neuropathy has been defined as a peripheralneuropathy manifest by paresthesias with findings of small-fiber dysfunction on examination, specialized testing (e.g.,

ASSURE

Software failures in server applications are a significant problem for preserving system availability. We present ASSURE, a system that introduces rescue points that recover software from unknown faults while maintaining both system integrity and availability, by mimicking system behavior under known error conditions. Rescue points are locations in existing application code for handling a given set of programmer-anticipated failures, which are automatically repurposed and tested for safely enabling fault recovery from a larger class of (unanticipated) faults. When a fault occurs at an arbitrary location in the program, ASSURE restores execution to an appropriate rescue point and induces the program to recover execution by virtualizing the program's existing error-handling facilities. Rescue points are identified using fuzzing, implemented using a fast coordinated checkpoint-restart mechanism that handles multi-process and multi-threaded applications, and, after testing, are injected into production code using binary patching. We have implemented an ASSURE Linux prototype that operates without application source code and without base operating system kernel changes. Our experimental results on a set of real-world server applications and bugs show that ASSURE enabled recovery for all of the bugs tested with fast recovery times, has modest performance overhead, and provides automatic self-healing orders of magnitude faster than current human-driven patch deployment methods.

ASSURE

Software failures in server applications are a significant problem for preserving system availability. We present ASSURE, a system that introduces rescue points that recover software from unknown faults while maintaining both system integrity and availability, by mimicking system behavior under known error conditions. Rescue points are locations in existing application code for handling a given set of programmer-anticipated failures, which are automatically repurposed and tested for safely enabling fault recovery from a larger class of (unanticipated) faults. When a fault occurs at an arbitrary location in the program, ASSURE restores execution to an appropriate rescue point and induces the program to recover execution by virtualizing the program's existing error-handling facilities. Rescue points are identified using fuzzing, implemented using a fast coordinated checkpoint-restart mechanism that handles multi-process and multi-threaded applications, and, after testing, are injected into production code using binary patching. We have implemented an ASSURE Linux prototype that operates without application source code and without base operating system kernel changes. Our experimental results on a set of real-world server applications and bugs show that ASSURE enabled recovery for all of the bugs tested with fast recovery times, has modest performance overhead, and provides automatic self-healing orders of magnitude faster than current human-driven patch deployment methods.

Food quality affects search strategy in the acellular slime mould, Physarum polycephalum

When searching for resources, organisms can increase the efficiency of search and exploitation behavior by using information about the quality of a current resource patch in their decision making. The search strategy used by an organism can in turn affect its performance in different landscapes. Here we examine the effect of resource quality on 2 foraging decisions: how much time to allocate to explore the environment for new resources and what search strategy to use during exploration. We used the slime mould Physarum polycephalum as our model system. Physarum polycephalum is an amoeboid organism that forages as a flowing mass of pseudopods. We quantified the search pattern of plasmodia after engulfment of food of 6 different qualities. Food quality had a significant, positive effect on how long plasmodia waited before resuming search behavior and on how long it took to abandon food disks. Food quality had a positive effect on fractal dimension, indicating that the amount of localized search performed by plasmodia increased with food quality. Our results suggest that increasing food quality results in a shift from extensive to intensive search. Next, we examined foraging performance in landscapes with different patch structures. Plasmodia in correlated landscapes (half the patches contained only high-quality food, half contained only low-quality food) gained more weight than plasmodia foraging in noncorrelated landscapes (patches contained both high- and low-quality food disks). Our results show that food quality affects exploitation and search behavior and that both behaviors influence foraging performance in different landscapes. Key words: amoeboid, area-restricted search, exploitation, exploration, foraging, myxomycophyta. [Behav Ecol]

Differential use of conspecific-derived information by sexual and asexual parasitic wasps exploiting partially depleted host patches

When foraging partially depleted patches (i.e., a fraction of hosts are already parasitized), female parasitoids must decide: 1—whether to superparasitize, and 2—whether to stay in their current patch (thus missing the opportunity of finding a better patch elsewhere). To make these decisions, parasitoids may rely on different cues, produced both by the environment and by conspecifics. Animals thriving in different environments may differ in cues they use. In the solitary parasitoid Venturia canescens, thelytokous (asexual) and arrhenotokous (sexual) individuals are found in two contrasting environments. Thelytokous females, from anthropogenic conditions, are known to cope with superparasitism in an adaptive way. On the other hand, little is known about superparasitism by arrhenotokous females. We compared the host exploitation strategies of thelytokous and arrhenotokous females in partially depleted patches. Hosts parasitized by thelytokous females were more frequently avoided than those parasitized by arrhenotokous females, suggesting a stronger chemical marking of the former. Only thelytokous females used information from conspecifics for patch-leaving decisions. The conformity of the differences in the behavior of thelytokous and arrhenotokous females with the environmental conditions they experience in their habitat is discussed.

Inflexible wasps: the aphid parasitoid Lysiphlebus testaceipes does not track multiple changes in habitat profitability

Bayesian updating is a form of learning by which individuals can adapt their behaviour to uncertain environments. In the particular situation of optimal foraging in a patchy habitat, animals may estimate the profitability of the patches they encounter to update their estimate of the profitability of the habitat as a whole, and adjust their foraging decisions accordingly. Recent studies have suggested that parasitoid insects may have such abilities, but were based on too few patches for clear conclusions on Bayesian updating. We studied how females of an aphid parasitoid update their estimate of habitat profitability, by recording their behaviour on a series of seven consecutive host patches, each serving both as a potential cue for habitat profitability and as a means to measure the behavioural response to previously collected information. The experiment was designed to test specific predictions based on Bayesian updating with different memory dynamics. The parasitoids clearly perceived the profitability of the patches, but the effect of previous experience on current patch use was different from our predictions. The reinterpretation of previous studies in the light of our results suggests that foraging parasitoids give more weight to early experience.

TIME OF DAY AND FLIGHTINESS IN FLOCKS OF SEMIPALMATED SANDPIPERS

Environmental light intensity is known to exert a strong influence on antipredation behavior by influencing prey vulnerability. However, an association between low light levels and increased predation risk is not well established empirically. For species that rely on visual detection of their predators, low light levels can hinder predator detection and thus increase predation risk. We examined the foraging behavior of migrating Semipalmated Sandpipers (Calidris pusilla) on a mudflat in the Bay of Fundy in New Brunswick, Canada as a function of time of day from dawn to dusk. Time of day was used as a surrogate for light intensity, assuming that, on average, light levels would be lower near sunrise and sunset. Sandpipers forage both day and night at low tide, which occurs at different times each day, thus disentangling the effect of light intensity from energy levels. Falcons make surprise attacks on sandpipers by leaving forest cover and flying low over the mudflat, rendering detection difficult against the dark forest background. The propensity for sandpipers to leave a foraging patch by taking flight was higher earlier and later in the day, controlling for temperature and sandpiper density. Pecking success was similar whether a focal sandpiper stayed in the current patch or took flight at the end of a focal observation, suggesting that the choice to leave abruptly was not related directly to food availability. We conclude that increased flightiness likely represents a response by sandpipers to a perception of higher predation risk from falcon attacks at low light levels.

Smooth muscle specific knockdown of L‐type calcium channel by exogenous microRNA (miRNA)

In spontaneously hypertensive rats, vascular L‐type calcium channel pore forming α1 subunit (Cav1.2) protein expression, L‐type calcium current (CaL) and vascular tone are all increased, due to increased expression of the ubiquitously expressed isoform containing an exon 1b encoded N‐terminus. The objective of this study is to develop shRNA or miRNA constructs against the non‐cardiac form of Cav1.2 (exon1b isoform) to reverse the upregulation in a tissue‐specific manner. Cav1.2 exon 1b‐specific shRNA, miRNA, and appropriate controls were constructed and tested for silencing effects. In HEK cells, rat Cav1.2 expression vector (rCav1.2) was cotransfected with different constructs, CMV promoter‐driven miRNA (Cav1.2) had the strongest effect and decreased rCav1.2 protein ∼72%. More interestingly, miRNA(Cav1.2) driven by the vascular smooth muscle‐specific promoter SM22α reduced endogenous Cav1.2 expression (western blot) ∼51% and decreased CaL (barium) current (patch clamp) ∼46% in transfected A7r5 cells. Moreover, the SM22‐GFP‐miRNA(Cav1.2) had no effect on cotransfected rCav1.2 expression in HEK cells and showed little or no GFP expression in PC12 or HL1 cells.Conclusion:SM22–GFP‐miRNA(Cav1.2) can effectively and smooth muscle‐specifically reduce Cav1.2 expression. Coupled to adeno‐associated virus, this may provide a novel long‐term therapy for hypertension. Supported by NIH HL63903.

Characterization of a functional (pro)renin receptor (PRR) in brain neuron

Discovery of PRR has provided a novel mechanism by which RAS can influence the cardiovascular system. Initial findings from the kidney suggest that (pro)renin binding to PRR initiates a signaling cascade that leads to an angiotensin‐independent physiological responses. While knowledge is limited for the periphery, even less is known of PRR function in the brain. Thus our objectives in this study were to determine if PRR exists in the brain and if it is functional. Primary cell cultures from WKY rat brain were used in this study. Levels of PRR mRNA were 2.4 fold higher in neuronal compared to astroglial cultures. Immunofluorescence in neurons showed that PRR were localized both throughout the soma and in neurites as immunoreactive punctae. Treatment of neurons with renin in the presence of 2 μM losartan, caused a time‐ and dose‐dependent, transient increase in phosphorylation of p42 and p44 isoforms of MAP kinase. Phosphorylation peaked at 4 fold by 2 min with 20 nM renin. Current patch clamp recordings showed that neurons treated with renin, in the presence of losartan, resulted in a steady and stable decrease in action potential frequency to 56 % of basal within 5 min. This renin‐mediated decrease was blocked by pretreatment with MAP kinase inhibitor, PD89059. These results demonstrate that neurons from rat brain express functional PRR that is coupled to MAPK and neuronal activity. (Supported by NIH HL336 10)

Functional analysis of neuron-like cells differentiated from neural stem cells derived from bone marrow stroma cells in vitro.

The transversal differentiation of bone marrow stroma cell (BMSCs) into neural stem cells (NSCs) has attracted much attention in recent years because of their therapeutic potential. However, the problem in therapeutic application of NSCs was how to confirm whether neuron-like cells differentiated from bone marrow stroma cell-derived neural stem cells (BMSCs-D-NSCs) possess corresponding functions of neurochemistry and electrophysiology. In the present study, we tried to affirm the function of neuron-like cells differentiated from BMSCs-D-NSCs in vitro. The BMSCs were harvested by gradient centrifugation in Ficoll-Paque and cultured in "NSCs medium". Immunocytochemistry was used to detect positive expression of neuron-specific nuclear protein (NeuN) in neuron-like cells derived from the BMSCs-D-NSCs. High-pressure liquid chromatography (HPLC) was used to identify neuron-like cells by detecting excitable amino acids [aspartic acid (Asp), glutamic acid (Glu)], inhibited amino acids [glycine (Gly), gamma (gamma) -aminobutyric acid (GABA), alanine (Ala)] or monoamines [noradrenaline (NE), 5-hydroxytryptamine (5-HT), dopamine (DA)]. Electrophysiological properties of the neuron-like cells were also examined using patch clamp analysis to verify their neuron-like functions. It was found that the neuron-like cells differentiated from the BMSCs-D-NSCs could express positive NeuN, synthesize and excrete amino acids, and show some typical electrophysiological properties including the typical Na+ and K+ ion channel membrane current under the voltage patch clamp condition, the typical static electrical membrane potential under the current patch clamp condition, and the differential membrane capacitance and resistance values in series between undifferentiated BMSCs-D-NSCs and differentiated neuron-like cells under the whole-cell patch clamp condition. The neuron-like cells differentiated from BMSCs-D-NSCs exhibit both neuron-like biochemical function and some corresponding electrophysiological properties.

Management of calcareous grasslands for Nickerl’s fritillary (Melitaea aurelia) has to consider habitat requirements of the immature stages, isolation, and patch area

We analysed the habitat preferences of adult stages and oviposition electivity of Melitaea aurelia in calcareous grasslands in the Diemel Valley (central Germany) to assess the key factors for successful management. Egg-laying and adult habitats of M. aurelia were more or less congruent. Oviposition electivity at the host plant (Plantago media) was best explained by a combination of host plant quantity and vegetation structure. Habitat quality, isolation and patch area explained 86% of the current patch occupancy of M. aurelia. With M. aurelia preferentially inhabiting transitional vegetation types, management requires a balance between abandonment and disturbance. Disturbances provide open soil that facilitates germination of the host plant Plantago media. On the other hand, immature and adult stages of M. aurelia perform best on calcareous grasslands with a high amount of host plants and low disturbance intensity. Traditional rough grazing regimes seem to be the most favourable tool for developing the necessary spatial and temporal heterogeneity in patches. The best results may be achieved by rotational grazing where only a subset of inhabited patches is grazed intensively each year. Our analysis of patch occupancy indicates that it would be desirable to restore patches in close proximity to occupied sites.

Current patch test results in consecutive patients with, and chemical analysis of, disperse blue (DB) 106, DB 124, and the mix of DB 106 and 124

Disperse blue (DB) 106 and 124 are important textile dye allergens. However, the dye raw material is impure, leading to uncertainty regarding the actual patch test (PT) concentration. To examine, (i) the allergen content of previously and currently used DB 106 and 124 and a respective mix, and (ii) the frequency of positive PT reactions to the DB 106/124 mix and to the single compounds in consecutive PT patients. High performance liquid chromatography (HPLC) analysis and purification of DB 106 and 124, respectively. Descriptive analysis of PT data from the Information network of departments of dermatology obtained between January 2003 and December 2005. Retrospectively, 2 batches of the DB 106/124 mix proved to contain an amount of allergen different to the 1 declared (based on information of suppliers of raw material). However, since February 2005, DB 106 and 124, respectively, are available at a reliable concentration of 0.3% petrolatum. In 2005, the prevalence of positive PT reactions to both the mix (0.89%) and the single constituents combined (0.56%) did not qualify them for inclusion in the standard series. Quality control, providing accurate test concentrations of allergens based on technical grade purity raw materials is necessary for valid diagnosis of contact allergy and comparable epidemiological data.

Evidence against Functional Interaction between Aquaporin-4 Water Channels and Kir4.1 Potassium Channels in Retinal Müller Cells

Indirect evidence suggests that the Müller/glial cell water channel aquaporin-4 (AQP4) modulates K(+) channel function of the closely associated Kir4.1 protein. We used patch clamp to compare Kir4.1 K(+) channel function in freshly isolated Müller cells from retinas of wild-type (+/+) and AQP4 knock-out (-/-) mice. Immunocytochemistry showed a comparable Kir4.1 protein expression pattern in Müller cells from +/+ and -/- retinas, with greatest expression at their end feet. Osmotic water permeability was >4-fold reduced in -/- than in +/+ Müller cells. Resting membrane potential did not differ significantly in +/+ versus -/- Müller cells (-64 +/- 1 versus -64 +/- 1 mV, S.E., n = 24). Whole-cell K(+) currents recorded with a micropipette inserted into the cell soma were Ba(2+)-sensitive and showed no significant differences in magnitude in +/+ versus -/- Müller cells (1.3 +/- 0.1 versus 1.2 +/- 0.1 nA at -160 mV) or in inwardly rectifying current-voltage relationships. Spatially resolved K(+) currents generated by pulsed K(+) injections along Müller cell bodies were also comparable in +/+ versus -/- Müller cells. Single-channel cell-attached patch clamp showed comparable unitary conductance, current-voltage data, and open probability in +/+ versus -/- Müller cells. Thus, contrary to the generally accepted view, our results provide direct evidence against functionally significant AQP4 modulation of Müller cell Kir4.1 K(+) channel function.

Patch departure rules in Bumblebees: evidence of a decremental motivational mechanism

The patch living rules of a pollinator, the bumblebee Bombus terrestris L., are studied here in the framework of motivational models widely used for parasitoids: The rewarding events found during the foraging process are supposed to increase or decrease suddenly the tendency of the insect to stay in the current patch and therefore to adjust the patch residence time to the patch profitability. The foraging behaviour of these pollinators was observed in two environment types to determine their patch-leaving decisions. The rich environment was composed of male-fertile flowers, offering pollen and nectar, and the poor one of male-sterile flowers, offering little nectar and no pollen. The experimental design consisted of a patch system in which inflorescences were evenly arranged in two rows (1 m distance). Residence times of foragers inside inflorescences and rows were analysed by a Cox proportional hazards model, taking into account recent and past experience acquired during the foraging bout. Most of the results showed a decremental motivational mechanism, that is, a reduction in the residence time on the inflorescence or in the row related to exploitation of flowers within inflorescences and inflorescences within rows These results indicate that bumblebees tend to leave the patch using departure rules similar to those found in parasitoids. The results also provide information on the memory, learning and evaluating capabilities of bumblebees especially when rich and poor environments were compared. The patch-leaving mechanism suggested by this study is consistent with the central place foraging theory.

The Contraceptive Patch in Relation to Ischemic Stroke and Acute Myocardial Infarction

To compare rates of stroke and acute myocardial infarction in users of the Ortho EVRA contraceptive patch with these rates in users of norgestimate-containing oral contraceptives (OCs) with 35 microg of ethinyl estradiol. Retrospective, population-based, epidemiologic study. PharMetrics database. Females aged 15-45 years in the PharMetrics database who had filled at least one prescription for the Ortho EVRA contraceptive patch or a norgestimate OC between April 1, 2002, and March 31, 2005. Incidence rates and 95% confidence intervals (CI) were estimated for the outcomes of ischemic stroke and acute myocardial infarction by exposure. Crude incidence rates of ischemic stroke among users of the patch and users of norgestimate OCs were 13.6/100,000 woman-years (95% CI 5.9-26.8) and 11.3/100,000 woman-years (95% CI 5.4-20.8), respectively. The crude incidence rate of acute myocardial infarction was 1.7/100,000 woman-years (95% CI 0.04-9.5) in current patch users and 7.9/100,000 woman-years (95% CI 3.2-16.3) in current users of norgestimate OCs. Incidence rate ratios (IRRs) were estimated for the outcomes by comparing data for users of the patch and users of a norgestimate OC. The IRR for stroke was 1.2 (95% CI 0.41-3.4) and for acute myocardial infarction was 0.2 (95% CI 0.004-1.7). Ischemic stroke and acute myocardial infarction are rare among young women who use hormonal contraceptives, and the current data provide no suggestion of an increased risk of either ischemic stroke or acute myocardial infarction in users of the Ortho EVRA contraceptive patch compared with users of norgestimate OCs.

Neotyphodium impacts on soil nematode communities: rhizosphere- and litter-mediated interactions

There is a growing recognition that endophyte effects on host plant traits may be propagated through food chains. We studied Neotyphodium occultans effects on soil nematode communities mediated by current and past patch occupancy by endophyteinfected Lolium multiflorum populations. A microcosm experiment was performed to evaluate whether abundance and diversity of nematodes at different trophic levels were affected by endophyte infection through rhizosphere-mediated or littermediated effects. We found that presence of endophyte-infected plants and their aerial litter both triggered a bottom-up trophic cascade enhancing the abundance of herbivorous and predaceous nematode taxa. Endophyte infection also increased overall nematode richness, mostly through changes induced at the highest trophic level in this soil food web. Our results suggest that fungal endophytes can modify the linkages between aboveand belowground community compartments, with potential consequences on plant patch dynamics. Keywords: soil food webs, Lolium multiflorum, Neotyphodium occultans, plant-soil feedback, after-life effects, indirect interactions, trophic cascades

MOVEMENT OF FORAGING TUNDRA SWANS EXPLAINED BY SPATIAL PATTERN IN CRYPTIC FOOD DENSITIES

We tested whether Tundra Swans use information on the spatial distribution of cryptic food items (below ground Sago pondweed tubers) to shape their movement paths. In a continuous environment, swans create their own food patches by digging craters, which they exploit in several feeding bouts. Series of short (<1 m) intra-patch movements alternate with longer inter-patch movements (>1 m). Tuber biomass densities showed a positive spatial auto-correlation at a short distance (<3 m), but not at a larger distance (3-8 m). Based on the spatial pattern of the food distribution (which is assumed to be pre-harvest information for the swan) and the energy costs and benefits for different food densities at various distances, we calculated the optimal length of an inter-patch movement. A swan that moves to the patch with the highest gain rate was predicted to move to the adjacent patch (at 1 m) if the food density in the current patch had been high (>25 g/m2) and to a more distant patch (at 7-8 m) if the food density in the current patch had been low (<25 g/m2). This prediction was tested by measuring the response of swans to manipulated tuber densities. In accordance with our predictions, swans moved a long distance (>3 m) from a low-density patch and a short distance (<3 m) from a high-density patch. The quantitative agreement between prediction and observation was greater for swans feeding in pairs than for solitary swans. The result of this movement strategy is that swans visit high-density patches at a higher frequency than on offer and, consequently, achieve a 38% higher long-term gain rate. Swans also take advantage of spatial variance in food abundance by regulating the time in patches, staying longer and consuming more food from rich than from poor patches. We can conclude that the shape of the foraging path is a reflection of the spatial pattern in the distribution of tuber densities and can be understood from an optimal foraging perspective.

Painful Peripheral Nerve Injury Decreases Calcium Current in Axotomized Sensory Neurons

Reports of Ca(2+) current I(Ca) loss after injury to peripheral sensory neurons do not discriminate between axotomized and spared neurons. The spinal nerve ligation model separates axotomized from spared neurons innervating the same site. The authors hypothesized that I(Ca) loss is a result of neuronal injury, so they compared axotomized L5 dorsal root ganglion neurons to spared L4 neurons, as well as neurons from rats undergoing skin incision alone. After behavioral testing, dissociated neurons from L4 and L5 dorsal root ganglia were studied in both current and voltage patch clamp modes. The biophysical consequence of I(Ca) loss on the action potential was confirmed using selective I(Ca) antagonists. Data were grouped into small, medium, and large cells for comparison. Reduced I(Ca) was predominantly a consequence of axotomy (L5 after spinal nerve ligation) and was most evident in small and medium neurons. ICa losses were associated with action potential prolongation in small and medium cells, whereas the amplitude and duration of after hyperpolarization was reduced in medium and large neurons. Blockade with Ca(2+) channel antagonists showed that action potential prolongation and after hyperpolarization diminution were alike, attributable to the loss of I(Ca). Axotomy is required for I(Ca) loss. I(Ca) loss correlated with changes in the biophysical properties of sensory neuron membranes during action potential generation, which were due to I(Ca) loss leading to decreased outward Ca(2+)-sensitive K currents. Taken together, these results suggest that neuropathic pain may be mediated, in part, by loss of I(Ca) and the cellular processes dependent on Ca(2+).

The foraging benefits of information and the penalty of ignorance

Patch use theory and the marginal value theorem predict that a foraging patch should be abandoned when the costs and benefits of foraging in the patch are equal. This has generally been interpreted as all patches being abandoned when their instantaneous intake rate equals the foraging costs. Bayesian foraging – patch departure is based on a prior estimate of patch qualities and sampling information from the current patch – predicts that instantaneous quitting harvest rates sometimes are not constant across patches but increase with search time in the patch. That is, correct Bayesian foraging theory has appeared incompatible with the widely accepted cost–benefit theories of foraging. In this paper we reconcile Bayesian foraging with cost–benefit theories. The general solution is that a patch should be left not when instantaneous quitting harvest rate reaches a constant level, but when potential quitting harvest rate does. That is, the forager should base its decision on the value now and in the future until the patch is left. We define the difference between potential and instantaneous quitting harvest rates as the foraging benefit of information, FBI. For clumped prey the FBI is positive, and by including this additional benefit of patch harvest the forager is able to reduce its penalty of ignorance.