Spatial distribution characteristics of stomata at the areole level in Michelia cavaleriei var. platypetala (Magnoliaceae)

Background and AimsIn hierarchically reticulate venation patterns, smaller orders of veins form areoles in which stomata are located. This study aimed to quantify the spatial relationship among stomata at the areole level.MethodsFor each of 12 leaves of M. cavaleriei var. platypetala, we assumed that stomatal characteristics were symmetrical on either side of the midrib, and divided the leaf surface on one side of the midrib into six layers equidistantly spaced along the apical–basal axis. We then further divided each layer into three positions equidistantly spaced from midrib to leaf margin, resulting in a total of 18 sampling locations. In addition, for 60 leaves, we sampled three positions from midrib to margin within only the widest layer of the leaf. Stomatal density and mean nearest neighbour distance (MNND) were calculated for each section. A replicated spatial point pattern approach quantified stomatal spatial relationships at different distances (0–300 μm).Key ResultsA tendency towards regular arrangement (inhibition as opposed to attraction or clustering) was observed between stomatal centres at distances <100 μm. Leaf layer (leaf length dimension) had no significant effect on local stomatal density, MNND or the spatial distribution characteristics of stomatal centres. In addition, we did not find greater inhibition at the centre of areoles, and in positions farther from the midrib.ConclusionsSpatial inhibition might be caused by the one-cell-spacing rule, resulting in more regular arrangement of stomata, and it was found to exist at distances up to ~100 μm. This work implies that leaf hydraulic architecture, consisting of both vascular and mesophyll properties, is sufficient to prevent important spatial variability in water supply at the areole level.     

辽东山区次生林乔木幼苗组成及其年际动态

为了解辽东山区次生林乔木幼苗组成及其年际动态, 本文以4 ha动态监测样地为平台, 对样地内1,600个 5 m × 5 m样方进行监测。依据2014-2016年连续3年的调查, 对样地内乔木幼苗的组成、高度分布、新增和死亡年际动态、空间分布格局等进行分析。结果表明: (1)调查期间共记录到22种乔木幼苗, 3年间幼苗组成没有发生变化, 但各个样方间出现极大差异, 并且幼苗优势树种组成与样地内优势树种成分保持着一定的相似性。(2)幼苗数量在不同树种和年际间表现出较大的差异: 花曲柳(Fraxinus rhynchophylla)、色木槭(Acer mono)、胡桃楸(Juglans mandshurica)在3年间幼苗数量最多, 占幼苗总数的75.6%; 花曲柳和胡桃楸幼苗数量表现出较明显的年际波动, 其他树种波动较小, 不同树种的幼苗密度差异很大。(3)幼苗新增和死亡存在明显的种间和年际差异: 2014-2015年间幼苗的新增数量(3,888)明显高于2015-2016年间(1,710), 同时2014-2015年间幼苗死亡率(23.7%)也明显高于2015-2016年间(12.7%)。对2015-2016年间新增幼苗和已有幼苗的死亡情况进行比较可以发现, 新增幼苗总体死亡率(18.8%)明显高于已有幼苗(8.1%)。(4)对比幼苗和大树的空间分布可以发现, 样地内优势幼苗都表现出集群分布的特征。在空间分布上, 幼苗与母树保持一定的相似性。     

食物和季节因素对杂色山雀贮食行为的影响

鸟类的贮食行为受很多因素的影响,其中食物和季节是两个十分关键的因子。采用人工投食的方式研究杂色山雀冬、春季节对松子和葵花籽两种食物的贮食选择,以及食物和季节因素对贮食位点的空间分布和微生境选择的影响。结果发现,杂色山雀优先贮食松子,仅在春季贮食少量葵花籽;主要选择树皮裂缝、灌木根部、草丛、石缝和苔藓下面五种生境进行贮食;其贮食位点的空间分布呈分散状态,集中于投食点100m范围内,密度分布随食物搬运距离的增加而递减。其贮食模式和贮食位点的微生境选择均受季节因素的影响,其中,贮食模式的季节变化可能是受生境中松子这种重要食物可获得性的下降所致,而杂色山雀冬季对树皮裂缝的利用率明显高于春季,可能是与冬季的积雪覆盖限制了其对地面贮食点的利用有关。杂色山雀的就近贮食模式可能是为了增加贮食效率,关于不同个体之间贮食位点的差异,以及季节变化对贮食位点的空间分布格局的影响还需进一步研究。     

Spatial properties of astrocyte gap junction coupling in the rat hippocampus

Gap junction coupling enables astrocytes to form large networks. Its strength determines how easily a signalling molecule diffuses through the network and how far a locally initiated signal can spread. Changes of coupling strength are well-documented during development and in response to various stimuli. Precise quantification of coupling is needed for studying such modifications and their functional consequences. We therefore explored spatial properties of astrocyte coupling in a model simulating dye loading of single astrocytes. Dye spread into the astrocyte network could be characterized by a coupling length constant and coupling anisotropy. In experiments, the fluorescent marker Alexa Fluor 594 was used to measure these parameters in CA1 and dentate gyrus of the rat hippocampus. Coupling did not differ between regions but showed a temperature-dependence, partially owing to changes of intracellular diffusivity, detected by measuring coupling length constants but not the more variable cell counts of dye-coupled astrocytes. We further found that coupling is anisotropic depending on distance to the pyramidal cell layer, which correlated with regional differences of astrocyte morphology. This demonstrates that applying these new analytical approaches provides useful quantitative information on gap junction coupling and its heterogeneity.     

Hippocampal NMDA receptors are important for behavioural inhibition but not for encoding associative spatial memories

The idea that an NMDA receptor (NMDAR)-dependent long-term potentiation-like process in the hippocampus is the neural substrate for associative spatial learning and memory has proved to be extremely popular and influential. However, we recently reported that mice lacking NMDARs in dentate gyrus and CA1 hippocampal subfields (GluN1^ΔDGCA1 mice) acquired the open field, spatial reference memory watermaze task as well as controls, a result that directly challenges this view. Here, we show that GluN1^ΔDGCA1 mice were not impaired during acquisition of a spatial discrimination watermaze task, during which mice had to choose between two visually identical beacons, based on extramaze spatial cues, when all trials started at locations equidistant between the two beacons. They were subsequently impaired on test trials starting from close to the decoy beacon, conducted post-acquisition. GluN1^ΔDGCA1 mice were also impaired during reversal of this spatial discrimination. Thus, contrary to the widely held belief, hippocampal NMDARs are not required for encoding associative, long-term spatial memories. Instead, hippocampal NMDARs, particularly in CA1, act as part of a comparator system to detect and resolve conflicts arising when two competing, behavioural response options are evoked concurrently, through activation of a behavioural inhibition system. These results have important implications for current theories of hippocampal function.     

ON THE EVOLUTION OF MIGRATION IN HETEROGENEOUS ENVIRONMENTS

Populations often experience variable conditions, both in time and space. Here we develop a novel theoretical framework to study the evolution of migration under the influence of spatially and temporally variable selection and genetic drift. First, we examine when polymorphism is maintained at a locus under heterogeneous selection, as a function of the pattern of spatial heterogeneity and the migration rate. In a second step, we study how levels of migration evolve under the joint action of kin competition and local adaptation at a polymorphic locus. This analysis reveals the existence of evolutionary bistability, whereby a low or a high migration rate may evolve depending on the initial conditions. Last, we relax several assumptions regarding selection heterogeneity commonly made in previous studies and explore the consequences of more complex spatial and temporal patterns of variability in selection on the evolution of migration. We found that small modifications in the pattern of environmental heterogeneity may have dramatic effects on the evolution of migration. This work highlights the importance of considering more general scenarios of environmental heterogeneity when studying the evolution of life‐history traits in ecologically complex settings.