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81.
82.
Leif Sönnichsen Matthijs Bokje Jessica Marchal Heribert Hofer Bogumiła Jędrzejewska Stephanie Kramer‐Schadt Sylvia Ortmann 《Ethology : formerly Zeitschrift fur Tierpsychologie》2013,119(3):233-243
In natural environments, predation risk varies over time. The risk allocation hypothesis predicts that prey is expected to adjust key anti‐predator behaviours such as vigilance to temporal variation in risk. We tested the predictions of the risk allocation hypothesis in a natural environment where both a species‐rich natural predator community and human hunters are abundant and where the differences in seasonal and circadian activity between natural and anthropogenic predators provided a unique opportunity to quantify the contributions of different predator classes to anti‐predator behaviour. Whereas natural predators were expected to show similar levels of activity throughout the seasons, hunter activity was high during the daytime during a clearly defined hunting season. According to the risk allocation hypothesis, vigilance should then be higher during the hunting season and during daytime hours than during the non‐hunting season and night‐time hours. Roe deer (Capreolus capreolus) on the edge of Bia?owie?a Primeval Forest in Eastern Poland displayed vigilance behaviour consistent with these predictions. The behavioural response of roe deer to temporarily varying predation risks emphasises the behavioural plasticity of this species and suggests that future studies of anti‐predator behaviour need to incorporate circadian variation in predation pressure as well as risk gradients of both natural and anthropogenic predators. 相似文献
83.
Dormant propagule pools (egg banks) of zooplankton populations that accumulate in sediments provide biological archives of past conditions and enable the investigation of evolutionary changes in populations over relatively long periods of time (many decades). This study examined the egg bank of a Daphnia pulicaria population in a lake that has been stocked annually with rainbow trout (a zooplanktivore) since 1961. Resting eggs from sediments from the 1920s to 2001 (determined by 210Pb dating) were hatched and established as isofemale clonal lines. The phototactic behavior (a proxy for vertical migration behavior) of clones was assessed in the presence and absence of fish kairomones to evaluate the hypothesis that the heavy and consistent level of predation imposed by the stocked trout would have selected for clones that are more negatively phototactic. In addition, exposure to kairomones was expected to induce stronger negative phototaxis for all clones relative to control conditions. The behavior of clones derived from resting eggs from the trout era (after 1961) was significantly more negatively phototactic than it was for pre-trout era clones. Kairomone exposure induced a more negative phototactic response in clones from both eras, but the response was much greater for the pre-trout era clones. These results suggest that the consistently high level of predation by trout over several decades has selected for a conservative (less plastic) vertical migration strategy in which Daphnia maintain a deep daytime distribution with or without the presence of chemical cues from fish predators. 相似文献
84.
Valentina D.A. Corino Frida Sandberg Federico Lombardi Luca T. Mainardi Leif Sörnmo 《Biomedical signal processing and control》2013,8(6):1017-1025
Statistical modeling of atrioventricular (AV) nodal function during atrial fibrillation (AF) is revisited for the purpose of defining model properties and improving parameter estimation. The characterization of AV nodal pathways is made more detailed and the number of pathways is now determined by the Bayesian information criterion, rather than just producing a probability as was previously done. Robust estimation of the shorter refractory period (i.e., of the slow pathway) is accomplished by a Hough-based technique which is applied to a Poincaré plot of RR intervals. The performance is evaluated on simulated data as well as on ECG data acquired from AF patients during rest and head-up tilt test. The simulation results suggest that the refractory period of the slow pathway can be accurately estimated even in the presence of many artifacts. They also show that the number of pathways can be accurately determined. The results from ECG data show that the refined AV node model provides significantly better fit than did the original model, increasing from 85 ± 5% to 88 ± 4% during rest, and from 86 ± 5% to 87 ± 3% during tilt. When assessing the effect of sympathetic stimulation, the AF frequency increased significantly during tilt (6.25 ± 0.58 Hz vs. 6.32 ± 0.61 Hz, p < 0.05, rest vs. tilt) and the prolongation of the refractory periods of both pathways decreased significantly (slow pathway: 0.23 ± 0.20 s vs. 0.11 ± 0.10 s, p < 0.001, rest vs. tilt; fast pathway: 0.24 ± 0.31 s vs. 0.16 ± 0.19 s, p < 0.05, rest vs. tilt). The results show that AV node characteristics can be assessed noninvasively for the purpose of quantifying changes induced by autonomic stimulation. 相似文献
85.
Alanna Weisman Vera Bril Mylan Ngo Leif E. Lovblom Elise M. Halpern Andrej Orszag Bruce A. Perkins 《PloS one》2013,8(3)
Objective
Evaluation of diabetic sensorimotor polyneuropathy (DSP) is hindered by the need for complex nerve conduction study (NCS) protocols and lack of predictive biomarkers. We aimed to determine the performance of single and simple combinations of NCS parameters for identification and future prediction of DSP.Materials and Methods
406 participants (61 with type 1 diabetes and 345 with type 2 diabetes) with a broad spectrum of neuropathy, from none to severe, underwent NCS to determine presence or absence of DSP for cross-sectional (concurrent validity) analysis. The 109 participants without baseline DSP were re-evaluated for its future onset (predictive validity). Performance of NCS parameters was compared by area under the receiver operating characteristic curve (AROC).Results
At baseline there were 246 (60%) Prevalent Cases. After 3.9 years mean follow-up, 25 (23%) of the 109 Prevalent Controls that were followed became Incident DSP Cases. Threshold values for peroneal conduction velocity and sural amplitude potential best identified Prevalent Cases (AROC 0.90 and 0.83, sensitivity 80 and 83%, specificity 89 and 72%, respectively). Baseline tibial F-wave latency, peroneal conduction velocity and the sum of three lower limb nerve conduction velocities (sural, peroneal, and tibial) best predicted 4-year incidence (AROC 0.79, 0.79, and 0.85; sensitivity 79, 70, and 81%; specificity 63, 74 and 77%, respectively).Discussion
Individual NCS parameters or their simple combinations are valid measures for identification and future prediction of DSP. Further research into the predictive roles of tibial F-wave latencies, peroneal conduction velocity, and sum of conduction velocities as markers of incipient nerve injury is needed to risk-stratify individuals for clinical and research protocols. 相似文献86.
Alon Abraham Majed Alabdali Abdulla Alsulaiman Ari Breiner Carolina Barnett Hans D. Katzberg Leif E. Lovblom Bruce A. Perkins Vera Bril 《PloS one》2016,11(11)
IntroductionSmall fiber neuropathy might be a part of typical mixed small and large fiber neuropathy, or a distinct entity, affecting exclusively small nerve fibers.ObjectivesExplore the utility of small nerve fiber testing in patients with clinical presentation suggesting small fiber neuropathy, with and without evidence for concomitant large fiber neuropathy.MethodsPatients attending the neuromuscular clinic from 2012 to 2015 with a clinical presentation suggesting small nerve fiber impairment, who had Laser Doppler flare imaging (LDIFlare) and quantitative thermal testing (QTT) were evaluated for this study. Patients with clinical or electrophysiological evidence for concomitant large fiber neuropathy were not excluded.ResultsThe sensitivities of LDIFlare, cooling and heat threshold testing were 64%, 36%, and 0% respectively for clinically highly suggestive small fiber neuropathy, 64%, 56%, and 19% respectively for mixed fiber neuropathy, and 86%, 79%, and 29% respectively for diabetic mixed fiber neuropathy.DiscussionLDIFlare and cooling thresholds testing are non-invasive small nerve fiber testing modalities, with moderate performance in patients with small and mixed fiber neuropathy, and excellent performance in diabetic mixed fiber neuropathy. 相似文献
87.
Endoglin is required for myogenic differentiation potential of neural crest stem cells 总被引:1,自引:0,他引:1
Mancini ML Verdi JM Conley BA Nicola T Spicer DB Oxburgh LH Vary CP 《Developmental biology》2007,308(2):520-533
Genetic studies show that TGFbeta signaling is essential for vascular development, although the mechanism through which this pathway operates is incompletely understood. Here we demonstrate that the TGFbeta auxiliary coreceptor endoglin (eng, CD105) is expressed in a subset of neural crest stem cells (NCSCs) in vivo and is required for their myogenic differentiation. Overexpression of endoglin in the neural crest caused pericardial hemorrhaging, correlating with altered vascular smooth muscle cell investment in the walls of major vessels and upregulation of smooth muscle alpha-actin protein levels. Clonogenic differentiation assay of NCSCs derived from neural tube explants demonstrated that only NCSC expressing high levels of endoglin (NCSC(CD105+)) had myogenic differentiation potential. Furthermore, myogenic potential was deficient in NCSCs obtained from endoglin null embryos. Expression of endoglin in NCSCs declined with age, coinciding with a reduction in both smooth muscle differentiation potential and TGFbeta1 responsiveness. These findings demonstrate a cell autonomous role for endoglin in smooth muscle cell specification contributing to vascular integrity. 相似文献
88.
Engqvist L 《Evolution; international journal of organic evolution》2007,61(6):1489-1494
Theory predicts that when sperm compete numerically, selection will favor males who vary the number of sperm they transfer with the immediate level of sperm competition. In this study, I measured male mating investment in response to both female mating status (virgin vs. mated) and the number of foreign sperm stored by females in a previous mating in the scorpionfly Panorpa cognata. Female sperm storage was manipulated by interrupting copulations at different time points. Female mating status did not significantly influence male mating investment, but resource-limited males invested strategically in relation to the amount of sperm stored by females in a previous mating. I found continuously decreasing male investment in response to increasing amounts of competing sperm. These results demonstrate an unprecedented male ability to assess the number of sperm stored by females. As a result, males are capable of an extraordinarily fine-tuned reaction to the intensity of sperm competition. 相似文献
89.
90.
Grazing by large herbivores may negatively affect bird populations. This is of great conservation concern in areas with intensive sheep grazing. Sheep management varies substantially between regions, but no study has been performed in less intensively grazed systems. In a fully replicated, landscape scale experiment with three levels of sheep grazing, we tested whether the abundance and diversity of an assemblage of mountain birds were negatively affected by grazing or if grazing facilitated the bird assemblage. Density of birds was higher at high sheep density compared with low sheep density or no sheep by the fourth grazing season, while there was no clear effect on bird diversity. Thus, agricultural traditions and land use politics determining sheep density may change the density of avifauna in either positive or negative directions. 相似文献