为了评估距离，跳蛛会看绿色
一个日本的研究团队报告说，跳蛛有着一种帮助他们扑向其猎物的不同寻常的感知深度的系统。大多数的动物或是通过调节其眼中的晶状体的焦距（如人类那样），或是移动其头部以制造一种叫做运动视差的效果来评估与某个物体的距离。新的发现提示，跳蛛用的是一个叫做图像散焦的第三种选择，该方法涉及到将一个模糊的画面与一个清晰分明的画面进行比较。人类用画面散焦来对两个物体间的距离进行粗略估计——想想那些前景模糊但背景清楚的照片——但是到目前为止，没有一种已知的动物是用画面散焦来确定与某单个物体的距离的。Takashi Nagata及其同事的这些发现是通过分析跳蛛原发眼的四层视网膜中的每一层而做出的。说来奇怪，这些视网膜中有一层内含有一种绿敏色素，尽管事实上这一层视网膜不会聚焦绿光。因此，在正常的“白色”日光中，这一层总是会接收一种未聚焦的图像，而其他各层则会接收聚焦的图像。文章的作者估计，这一差别可允许该种蜘蛛通过画面散焦来估测某个物体的深度。让蜘蛛接触彩色的光线证实了这一假说，因为在绿光中的蜘蛛会做出精准的跳跃，但处在红光（在红光中，所有较短波长的光线，其中包括绿光都缺乏）中的蜘蛛几乎总是跳到还不到它们目标的地方。一则相关的《观点栏目》讨论了这一研究。
Depth Perception from Image Defocus in a Jumping Spider
The principal eyes of jumping spiders have a unique retina with four tiered photoreceptor layers, on each of which light of different wavelengths is focused by a lens with appreciable chromatic aberration. We found that all photoreceptors in both the deepest and second-deepest layers contain a green-sensitive visual pigment, although green light is only focused on the deepest layer. This mismatch indicates that the second-deepest layer always receives defocused images, which contain depth information of the scene in optical theory. Behavioral experiments revealed that depth perception in the spider was affected by the wavelength of the illuminating light, which affects the amount of defocus in the images resulting from chromatic aberration. Therefore, we propose a depth perception mechanism based on how much the retinal image is defocused.
文献链接：https://www.sciencemag.org/content/335/6067/469.abstract
蝗虫似乎会集结于低蛋白含量的农作物
新的研究证明，过多的蛋白质可能对亚洲小车蝗这种蝗虫是不利用的；这些蝗虫更可能会在那些植被氮含量低的地方大批集结。不幸的是，对许多农业经营者来说，土壤受到侵蚀及大规模的放牧都会降低农作物中的氮含量（并因而也降低其蛋白质的含量），从而增加了蝗虫大批集结的机会。Arianne Cease及其同事与大多数的研究人员都知道，最佳的饮食给生物体提供的是含量正好合适的蛋白质。但他们不确认的是，次佳饮食会如何影响在野外的物种。因此，研究人员对这一特别的蝗虫物种进行了研究；这种蝗虫是北亚草原上的一种主要的害虫。他们发现，高氮食物会使这种昆虫的大小和生存能力都有所下降。据研究人员披露，这些蝗虫似乎更喜欢吃氮含量低的植物，或是蛋白含量低但碳水化合物含量高的人工饲料。他们说，在那些植物氮含量最低、土壤中氮已经耗竭的高度放牧地区内，蝗虫的数量也是最大的。
Heavy Livestock Grazing Promotes Locust Outbreaks by Lowering Plant Nitrogen Content
Current paradigms generally assume that increased plant nitrogen (N) should enhance herbivore performance by relieving protein limitation, increasing herbivorous insect populations. We show, in contrast to this scenario, that host plant N enrichment and high-protein artificial diets decreased the size and viability of Oedaleus asiaticus, a dominant locust of north Asian grasslands. This locust preferred plants with low N content and artificial diets with low protein and high carbohydrate content. Plant N content was lowest and locust abundance highest in heavily livestock-grazed fields where soils were N-depleted, likely due to enhanced erosion. These results suggest that heavy livestock grazing and consequent steppe degradation in the Eurasian grassland promote outbreaks of this locust by reducing plant protein content.
文献链接：https://www.sciencemag.org/content/335/6067/467.abstract
朊蛋白的一种更快的进入方式
研究人员报告说，被称作朊蛋白的错误折叠蛋白可比通过脑组织更容易地通过淋巴样组织从一个物种传给另外一个物种。而且，据那些研究人员披露，这一发现应该促使人们对科学家们一般假设，即朊蛋白——造成诸如慢性消耗性疾病及“疯牛病”等人畜神经退行性病变的病原体不会轻易地在物种间转移的说法进行重新评估。在通常的情况下，所谓的物种屏障确实可阻止朊蛋白轻易地从一个物种传播给另外一个物种。但是，Vincent Béringue及其同事在研究了表达羊或人的朊蛋白或PrP的转基因小鼠后发现，淋巴样组织——包括那些存在于脾脏、扁桃体、阑尾和淋巴结中的淋巴样组织——常常要比脑组织更容易传播朊蛋白。
他们的发现提示，朊蛋白的“沉默”的携带者的数目——即那些带有该病原体但没有表达症状者的数目可能比先前以为的要更高。由John Collinge撰写的一篇《观点栏目》更为详细地解释了这些结果。
Facilitated Cross-Species Transmission of Prions in Extraneural Tissue
Prions are infectious pathogens essentially composed of PrPSc, an abnormally folded form of the host-encoded prion protein PrPC. Constrained steric interactions between PrPSc and PrPC are thought to provide prions with species specificity and to control cross-species transmission into other host populations, including humans. We compared the ability of brain and lymphoid tissues from ovine and human PrP transgenic mice to replicate foreign, inefficiently transmitted prions. Lymphoid tissue was consistently more permissive than the brain to prions such as those causing chronic wasting disease and bovine spongiform encephalopathy. Furthermore, when the transmission barrier was overcome through strain shifting in the brain, a distinct agent propagated in the spleen, which retained the ability to infect the original host. Thus, prion cross-species transmission efficacy can exhibit a marked tissue dependence.
文献链接：https://www.sciencemag.org/content/335/6067/472.abstract
