动物地磁导航机制研究进展

地磁场是地球重要的物理场,它不仅能保护地球生物免受太阳风及其他宇宙射线的伤害,阻挡地球生命赖以生存的大气圈和水圈被剥蚀,为地球生物提供一个温和的生存进化环境,而且其强度、偏角和倾角能为动物迁徙提供定位导航参考。目前,行为学研究已经发现许多鸟类、爬行类、两栖类、哺乳类等动物都能够利用地磁场导航。动物感知地磁场的磁感受器(magnetoreceptor)、磁信息的感知机制和信号传递通路一直是动物地磁导航研究的焦点和难点,但目前对它们的了解并不十分清楚。基于国内外学者最近的研究成果,本文首先介绍三种主要的磁感知机制及其相应的证据:电磁感应、基于光受体的磁感知及基于磁铁矿纳米颗粒的磁感知。其次,总结鸟类基于光受体和磁铁矿纳米颗粒的磁感知神经通路和相应的磁信息响应脑区:(1)眼睛视网膜上光依赖的磁感受器——隐花色素通过视觉通路与大脑联系获取准确方向信息;(2)上喙或内耳中的磁铁矿纳米颗粒磁感受器,通过三叉神经或内耳听壶传入神经将感知的磁场强度信息传至脑干前庭区域,获得"导航图"信息。最后,简要总结近年来哺乳动物地磁导航的研究进展,并指出动物地磁导航研究当前亟待解决的几个重要科学问题。     

Improving Accuracy and Precision in Estimating Fractal Dimension of Animal movement paths

It is difficult to watch wild animals while they move, so often biologists analyse characteristics of animal movement paths. One common path characteristic used is tortuousity, measured using the fractal dimension (D). The typical method for estimating fractal D, the divider method, is biased and imprecise. The bias occurs because the path length is truncated. I present a method for minimising the truncation error. The imprecision occurs because sometimes the divider steps land inside the bends of curves, and sometimes they miss the curves. I present three methods for minimising this variation and test the methods with simulated correlated random walks. The traditional divider method significantly overestimates fractal D when paths are short and the range of spatial scales is narrow. The best method to overcome these problems consists of walking the dividers forwards and backwards along the path, and then estimating the path length remaining at the end of the last divider step.     

Animal Minds and Animal Emotions

The possibility of conscious experiences of emotions in non-humananimals has been much less explored than that of conscious experiencesassociated with carrying out complex cognitive tasks. However,no great cognitive powers are needed to feel hunger or painand it may be that the capacity to feel emotions is widespreadin the animal kingdom. Since plants can show surprisingly sophisticated"choice" and "decision-making" mechanisms and yet we would notwish to imply that they are conscious, attribution of emotionsto animals has to be done with care. Whether or not an animalpossesses anticipatory mechanisms associated with positive andnegative reinforcement learning may be a guide as to whetherit has evolved emotions.     

Animal Protection Measures in Taiwan: Taiwanese Attitudes Toward the Animal Protection Law and Animal Shelters

This study used a questionnaire, self-administered by 387 Taiwanese citizens, to assess Taiwanese perception and knowledge of the Animal Protection Law and perception and use of animal shelters. Most respondents (87%) knew that Taiwan has legal protection for animals. A –5 to 5 summary score measured knowledge of companion animal dog-related legal requirements. The median score was 3, indicating that almost all respondents had inadequate knowledge about these requirements. Although more dog caregivers had adequate knowledge of the law than did nondog caregivers (prevalence ratio = 1.9, 95% confidence interval: 1.1, 3.2), only 19% had adequate knowledge. Although most respondents (81%) knew Taiwan has animal shelters, only 19 (5%) reported visiting or participating in shelter activities. Only 6 (32%) of shelter visitors or users had a "good or better" impression of services received. Despite low usage of animal shelters, most respondents thought shelters should accept (87%) and relocate (90%) unwanted animals, capture strays (64%), assist in finding lost pets (79%), and educate the public about responsible ownership (85%). More than half (52%) thought shelters should perform euthanasia.     

Olfactory Orientation and Navigation in Humans

Although predicted by theory, there is no direct evidence that an animal can define an arbitrary location in space as a coordinate location on an odor grid. Here we show that humans can do so. Using a spatial match-to-sample procedure, humans were led to a random location within a room diffused with two odors. After brief sampling and spatial disorientation, they had to return to this location. Over three conditions, participants had access to different sensory stimuli: olfactory only, visual only, and a final control condition with no olfactory, visual, or auditory stimuli. Humans located the target with higher accuracy in the olfaction-only condition than in the control condition and showed higher accuracy than chance. Thus a mechanism long proposed for the homing pigeon, the ability to define a location on a map constructed from chemical stimuli, may also be a navigational mechanism used by humans.     

Precision and accuracy in quantifying herbivory

1. Tissue removal by herbivores (i.e. herbivory) is a dominant interaction in most communities which has important impacts on natural and managed ecosystems. Despite the importance of herbivory, we lack a quantitative comparison of the efficacy of the most commonly used methods used to quantify herbivore damage. 2. We examined the factors that affect the precision and accuracy of visual and digital methods commonly used to quantify damage to leaves. 3. We created 224 digital leaves from four plant species. In a fully factorial design we manipulated leaf morphology and species, the location of damage (marginal or internal), estimation method (exact percentage or 25% bins), observer experience and expectancy bias (i.e., bias due to an expected result). Using 583 adult observers, we estimated the precision and accuracy of individuals' ability to visually estimate known levels of damage. In a third smaller experiment, we performed similar analyses using a digital scanner. 4. Across the first two experiments, individuals estimated damage with high precision (R² = 0.75 and 0.80) and accuracy (slope_{actual vs estimated} = 0.88 and 0.86). However, the precision and accuracy of estimates were influenced by plant species, the location of damage, and estimation method. Inexperienced individuals also overestimated low levels of damage, and this bias decreased with experience. Digital methods were precise (R² = 0.98) whereas accuracy was statistically indistinguishable from visual methods (slope = 0.91). 5. Visual estimates of damage provide the fastest and most cost‐effective method for quantifying herbivory, and our results show they can be precise and accurate. We use our results to provide specific recommendations for future research.     

Magnetic Navigation

Recent evidence suggests that some amphibians, reptiles and birds may be capable of homing using information about geographic position (“map” information) derived from subtle geographic gradients in the earth's magnetic field. The “magnetic map” hypothesis faces numerous theoretical difficulties, however, due to the extremely high level of sensitivity that would be necessary to detect natural magnetic gradients, and to the presence of spatial irregularities and temporal variation in the geomagnetic field that might make map coordinates derived from magnetic gradients unreliable. To date, the majority of studies carried out to test the magnetic map hypothesis have involved field observations of the effects on homing orientation of naturally occurring spatial or temporal variation in the geomagnetic field. While providing an important first step, these studies are subject to the criticism that the observed changes in homing orientation could result from effects on a magnetic compass, or some other unidentified component of the navigational system, rather than from effects on a magnetic map. The recent development of experimental systems in which navigational ability can be studied under controlled or semi-controlled laboratory conditions has opened up the possibility of using new experimental approaches to more rigorously test the magnetic map hypothesis. After briefly reviewing the available evidence of the geomagnetic field's involvement in the map component of homing, a simple graphical model is presented which describes how the home direction derived from a bicoordinate map varies as a function of the value of one of the map coordinates when the value of the second map coordinate is held constant. In studies of homing orientation in which the value of a specific magnetic field parameter (e.g., total intensity, inclination, etc.) can be varied independently of other putative map parameters, the graphical model can be used to generate qualitative predictions about the changes in the direction of homing orientation that should be observed if the magnetic field parameter being manipulated serves as one coordinate of a bicoordinate map. The relationship between the direction of homing orientation and the value of a putative magnetic map parameter can also be used to generate quantitative predictions about characteristics of the local gradient of that magnetic field parameter in the vicinity of the home site (i.e., the alignment and “home value” of the local gradient) which can then be compared with actual measured values. Together, the qualitative and quantitative predictions of the graphical model permit rigorous tests of whether one or both coordinates of a bicoordinate navigational map are derived from the geomagnetic field.