Regulation of ephrin‐A expression in compressed retinocollicular maps

Retinotopic maps can undergo compression and expansion in response to changes in target size, but the mechanism underlying this compensatory process has remained a mystery. The discovery of ephrins as molecular mediators of Sperry's chemoaffinity process allows a mechanistic approach to this important issue. In Syrian hamsters, neonatal, partial (PT) ablation of posterior superior colliculus (SC) leads to compression of the retinotopic map, independent of neural activity. Graded, repulsive EphA receptor/ephrin‐A ligand interactions direct the formation of the retinocollicular map, but whether ephrins might also be involved in map compression is unknown. To examine whether map compression might be directed by changes in the ephrin expression pattern, we compared ephrin‐A2 and ephrin‐A5 mRNA expression between normal SC and PT SC using in situ hybridization and quantitative real‐time PCR. We found that ephrin‐A ligand expression in the compressed maps was low anteriorly and high posteriorly, as in normal animals. Consistent with our hypothesis, the steepness of the ephrin gradient increased in the lesioned colliculi. Interestingly, overall levels of ephrin‐A2 and ‐A5 expression declined immediately after neonatal target damage, perhaps promoting axon outgrowth. These data establish a correlation between changes in ephrin‐A gradients and map compression, and suggest that ephrin‐A expression gradients may be regulated by target size. This in turn could lead to compression of the retinocollicular map onto the reduced target. These findings have important implications for mechanisms of recovery from traumatic brain injury. © 2012 Wiley Periodicals, Inc. Develop Neurobiol, 2013     

An ecosystem model-based estimate of changes in water availability differs from water proxies that are commonly used in species distribution models

Aim  To assess whether the water availability measures commonly used in species distribution models might be misleading because they do not account for the hydrological effects of changes in vegetation structure and functioning.
Location  Europe.
Methods  We compared different methods for estimating water availability in species distribution models with the soil water content predicted by a process-based ecosystem model. The latter also accounted for the hydrological effects of dynamic changes in vegetation structure and functioning, including potential physiological effects of increasing CO₂.
Results  All proxies showed similar patterns of water availability across Europe for current climate, but when projected into the future, the changes in the simpler water availability measures showed no correlation with those projected by the more complex ecosystem model, even if CO₂ effects were switched off.
Main conclusions  Results from species distribution modelling studies concerning future changes in species ranges and biodiversity should be interpreted with caution, and more process-based representations of the water balance of terrestrial ecosystems should be considered within these models.     

Using Agent-Based Models to Aid Reef Restoration: Enhancing Coral Cover and Topographic Complexity through the Spatial Arrangement of Coral Transplants

High coral cover and topographic complexity are favorable qualities of a healthy coral reef. Because coral reef restoration is expensive and coral growth is naturally slow, there is a need to strategically arrange coral transplants to maximize coral cover and topographic complexity. Similarly, it is important to understand how differences in the life history characteristics of coral transplants can influence changes in the structural attributes of coral reefs. This study utilizes agent‐based computer modeling to explore the different spatial scenarios of coral transplantation using corals with contrasting r‐ and K‐selected life histories. Spatial indexes are used to compare coral cover and topographic complexity at incremental time scales, within which disturbance events are of minor importance in spatial structuring. The outcomes of the model suggest that even‐spaced grided transplanting arrangements provide the fastest increase in coral cover and three‐dimensional habitat space (topographic complexity) across large temporal scales (<30 years) for corals with r‐selected life history strategies.     

Damage to artificial seedlings across a disturbed Afromontane forest landscape

Seedling mortality is an important demographic bottleneck for forest regeneration, yet the factors influencing recruitment are often poorly characterized across space and time. In African highlands, where extensive patches of previously disturbed forests remain in persistent shrub‐dominated states, patterns of damage to seedlings have not been examined in detail. We used artificial seedlings to determine how (non‐herbivory‐related) damage varies across a fragmented forest landscape in the Bwindi Impenetrable National Park, Uganda. A total of 848 artificial seedlings were established in 106 plots, each with 8 seedlings, across a gradient of environmental factors, including habitat type, topographic position, distance to water, and distance to human activity. We divided damage into that due to vertebrates, plant debris, and unknown agents. From our 16,960 monthly stem assessments, 1,289 damage events were recorded. The mean “seedling” damage per year (± 1 SE) was 59.5 ± 2.3%. Damage was significantly more frequent in sites dominated by short herbs (66.1 ± 3.0) than in sites dominated by shrubs (60.1 ± 2.6) and ferns (47.9 ± 2.7). The mean percentage of damage by each class of agents was 45.8 ± 2.1% for vertebrates, 21.4 ± 2.1% for plant debris, and 3.8 ± 0.6% for unknown agents. These rates surpass those reported in other montane forests, likely reflecting the density of large vertebrates in our site. Our results indicate that most damage to artificial seedlings arises from larger vertebrates but that most spatial variation in this damage reflects the impacts of falling plant debris. These damage processes appear sufficient to constrain the regeneration of tree species in areas where forest cover is patchy and fragmented.     

Neither species geographic range size,climatic envelope,nor intraspecific leaf trait variability capture habitat specialization in a hyperdiverse Amazonian forest

Many plant species exhibit strong association with topographic habitats at local scales. However, the historical biogeographic and physiological drivers of habitat specialization are still poorly understood, and there is a need for relatively easy‐to‐measure predictors of species habitat niche breadth. Here, we explore whether species geographic range, climatic envelope, or intraspecific variability in leaf traits is related to the degree of habitat specialization in a hyperdiverse tropical tree community in Amazonian Ecuador. Contrary to our expectations, we find no effect of the size of species geographic ranges, the diversity of climate a species experiences across its range, or intraspecific variability in leaf traits in predicting topographic habitat association in the ~300 most common tropical tree species in a 25‐ha tropical forest plot. In addition, there was no phylogenetic signal to habitat specialization. We conclude that species geographic range size, climatic niche breadth, and intraspecific variability in leaf traits fail to capture the habitat specialization patterns observed in this highly diverse tropical forest.     

The number and cycle of rat vibrissae according to topographic arrangement

This study investigated the cycle of rat vibrissae by counting their number relative to their topographic arrangement. The average duration of maintaining single or double vibrissal shafts was analyzed. The ratio of the lifetime of the single and double shafts was around 3:2 weeks. The rostral and caudal vibrissae had relatively short and long cyclic durations, respectively; this difference may be related to their length and function.     

Whole-mount Imaging of Mouse Embryo Sensory Axon Projections

The visualization of full-length neuronal projections in embryos is essential to gain an understanding of how mammalian neuronal networks develop. Here we describe a method to label in situ a subset of dorsal root ganglion (DRG) axon projections to assess their phenotypic characteristics using several genetically manipulated mouse lines. The TrkA-positive neurons are nociceptor neurons, dedicated to the transmission of pain signals. We utilize a TrkA^taulacZ mouse line to label the trajectories of all TrkA-positive peripheral axons in the intact mouse embryo. We further breed the TrkA^taulacZ line onto a Bax null background, which essentially abolishes neuronal apoptosis, in order to assess growth-related questions independently of possible effects of genetic manipulations on neuronal survival. Subsequently, genetically modified mice of interest are bred with the TrkA^taulacZ/Bax null line and are then ready for study using the techniques described herein. This presentation includes detailed information on mouse breeding plans, genotyping at the time of dissection, tissue preparation, staining and clearing to allow for visualization of full-length axonal trajectories in whole-mount preparation.     

浙江天童木本植物叶片性状空间变异的地统计学分析

探究叶片性状的空间变异性和环境关联性有助于我们理解植物对环境的适应策略和群落建构机制。该研究以浙江天童5 hm²大型动态样地所有胸径≥1 cm的木本植物为对象, 测定了20 253株个体的单叶面积、比叶面积和叶片干物质含量, 土壤总氮、总磷、总碳、pH值、体积含水率、容重和腐殖质, 以及海拔、坡度和凹凸度等; 并用地统计学等方法分析了叶片性状的空间变异性及其与环境因子的相关性。结果表明: 1)单叶面积的空间变异最大, 比叶面积次之, 叶片干物质含量最小。三者在0-5.16 m空间范围内表现出较弱的空间自相关, 其半变异函数的最优模型分别为高斯模型、指数模型和指数模型。2)叶片性状空间变异具有方向性, 单叶面积空间变异在东北-西南方向上最大, 在西北-东南方向上最小; 比叶面积和叶片干物质含量的空间变异均在西北-东南方向最大, 在东北-西南方向最小。3)单叶面积与地形因子显著负相关(r = -0.12, p < 0.0001); 比叶面积与土壤养分显著负相关(r = -0.16, p < 0.0001), 叶片干物质含量与土壤养分显著正相关(r = 0.13, p < 0.0001)。4)东北-西南方向上, 地形因子对单叶面积、比叶面积和叶片干物质含量空间变异的影响大于土壤养分; 西北-东南方向上, 地形因子对单叶面积空间变异的影响相对较大, 而土壤养分对比叶面积和叶片干物质含量空间变异的影响较大。总之, 在研究样地内, 植物叶片性状随空间距离和方向存在很大的变异性, 叶片性状与地形因子、土壤养分的关联性间接表明了环境过滤对群落构建的影响。     

The Lateral Hypothalamus Is Involved in the Pathway Mediating the Hypotensive Response to Cingulate Cortex-Cholinergic Stimulation

1. The injection of acetylcholine (ACh) into the medial prefrontal cortex (MPFC) caused marked hypotensive response in either unanesthetized or anesthetized rats.2. The present experiment was designed to investigate anatomical connections of the ACh injection site in the MPFC with putative autonomic-related brain nuclei, as well as their possible involvement in the mediation of the hypotensive response to ACh.3. For the above purpose, the bidirectional neuronal tracer biotinylated dextran amine (BDA) was injected into Cg1 and Cg3 areas, within the MPFC of male Wistar rats. Five days later the animals were sacrificed and brain slices were processed and analyzed to determine neuronal projections efferent from as well afferent to the MPFC.4. Neuronal staining was more prominent in regions ipsilateral to the BDA injection site. Prominent efferent projections of the MPFC were observed in the contralateral MPFC; ipsi- and contralateral amygdala and hypothalamus; ipsilateral septal area, diagonal band, and zona incerta.5. Similar but not equal patterns of neuronal labeling were observed when BDA injections were performed within the two adjacent MPFC areas. BDA injections centered in the ACh injection site in the Cg3 area caused strong labeling in the septal area and diagonal band as well as an overall hypothalamic labeling. Within the hypothalamus an intense cortical projection was observed in the lateral hypothalamus (LH). BDA injections into the Cg1 area caused a more evident labeling of the amygdaloid complex.6. Neuronal cell bodies were evident throughout the MPFC as well as in the sensory-motor cortex when BDA was injected into the LH, thus indicating a massive ipsilateral cortical projection from the Cg3 to the LH.7. Bilateral NMDA-induced lesions within the LH caused a significant attenuation of the depressor responses to ACh injection in the MPFC, whereas unilateral lesions were marginally effective. These results indicate the involvement of the LH in the mediation of the hypotensive response to ACh injection into the MPFC as well as the bilateral distribution of the hypotensive pathway.