Predation between prokaryotes and the origin of eukaryotes

Accumulating data suggest that the eukaryotic cell originated from a merger of two prokaryotes, an archaeal host and a bacterial endosymbiont. However, since prokaryotes are unable to perform phagocytosis, the means by which the endosymbiont entered its host is an enigma. We suggest that a predatory or parasitic interaction between prokaryotes provides a reasonable explanation for this conundrum. According to the model presented here, the host in this interaction was an anaerobic archaeon with a periplasm‐like space. The predator was a small (facultative) aerobic α‐proteobacterium, which penetrated and replicated within the host periplasm, and later became the mitochondria. Plausible conditions under which this interaction took place and circumstances that may have led to the contemporary complex eukaryotic cell are discussed.     

Links between viruses and prokaryotes throughout the water column along a North Atlantic latitudinal transect

Viruses are an abundant, diverse and dynamic component of marine ecosystems and have a key role in the biogeochemical processes of the ocean by controlling prokaryotic and phytoplankton abundance and diversity. However, most of the studies on virus–prokaryote interactions in marine environments have been performed in nearshore waters. To assess potential variations in the relation between viruses and prokaryotes in different oceanographic provinces, we determined viral and prokaryotic abundance and production throughout the water column along a latitudinal transect in the North Atlantic. Depth-related trends in prokaryotic and viral abundance (both decreasing by one order of magnitude from epi- to abyssopelagic waters), and prokaryotic production (decreasing by three orders of magnitude) were observed along the latitudinal transect. The virus-to-prokaryote ratio (VPR) increased from ∼19 in epipelagic to ∼53 in the bathy- and abyssopelagic waters. Although the lytic viral production decreased significantly with depth, the lysogenic viral production did not vary with depth. In bathypelagic waters, pronounced differences in prokaryotic and viral abundance were found among different oceanic provinces with lower leucine incorporation rates and higher VPRs in the North Atlantic Gyre province than in the provinces further north and south. The percentage of lysogeny increased from subpolar regions toward the more oligotrophic lower latitudes. Based on the observed trends over this latitudinal transect, we conclude that the viral–host interactions significantly change among different oceanic provinces in response to changes in the biotic and abiotic variables.     

Phosphate requirement of Anabaena oscillarioides and its ecological implications

Anabaena oscillarioides (pure culture isolated from Waikato River, lat. 38°S, long. 176°E, North Island, New Zealand) was shown to be phosphorous deficient with low internal cellular phosphours content and high induced alkaline phosphatase activity when it was grown in membrane-filtered river water in batch cultures under defined laboratory conditions. The calculated relatively high Ks (half-saturation substrate constant) for inorganic phosphate is 67 µg 1^–1, which is above usual river level for the nutrient. This explains the low density of the algae in the river where maximum growth is limited by low phosphorus concentration and the algae survive at suboptimal growth rate. Growth rate of the algae is proportional to phosphate concentration up to 100 µg 1^–1 beyond which increases in phosphate concentration only affects final yield. When the river was supplemented with 100 µg 1^–1 phosphate, the deficiency symptoms disappeared and the doubling time was reduced from two days to half a day.     

Vegetative incompatibility in the ash dieback pathogen Hymenoscyphus pseudoalbidus and its ecological implications

Pairings were carried out between isolates of the ash dieback pathogen Hymenoscyphus pseudoalbidus (Chalara fraxinea) to determine whether vegetative incompatibility (mycelial self–nonself recognition) reactions could be discriminated. On malt agar (MA) and ash sapwood agar (ASA) distinct compatible and incompatible reactions were observed. Compatible (C- or c-) reactions were characterised by full or partial colony intermingling along the junction line. Incompatible (G- or g-) reactions were characterised by a gap ca. 1–3 mm wide along the junction line. On MA a distinct narrow brown line or L-reaction was observed with some gap reactions, often comprising reticulate mycelium and conidia-producing phialides. When eleven isolates from a dieback site at Lower Wood, Norfolk were paired on ASA 53 of 54 reactions between different isolates gave incompatible reactions. A similar result was obtained with smaller samples from two further sites in Norfolk and Kent. This indicates that for local populations in the UK most genetic individuals of H. pseudoalbidus are likely to be vegetatively incompatible. The implications for the ecology and genetics of H. pseudoalbidus are discussed.     

丛枝菌根共生体的氮代谢运输及其生态作用

丛枝菌根真菌能与80%的陆生维管植物形成互惠共生关系,共生体的存在对促进植物营养吸收和提高抗逆性具有重要意义.丛枝菌根真菌从宿主植物获取其光合产物碳水化合物的同时,通过外生菌丝吸收各种氮源,有效增强了宿主植物对氮素的吸收,以及氮在植物居群和群落水平上的交流,改善了植物营养代谢,增强了植物应对外界环境胁迫的能力.而共生体对氮的吸收、转运,以及氮从真菌到宿主植物的传输、代谢机制至今仍有许多问题亟待解决.本文综述了当前丛枝菌根共生体中氮传输代谢的主要机制,以及碳、磷对共生体氮传输代谢的影响;从群落和生态系统水平,简要阐述了丛枝菌根真菌在植物中氮分配的作用和对宿主植物的生态学意义,并提出共生体中氮代谢的一些需要深入研究的问题.
     

斑块边缘效应的定量评价及其生态学意义

边缘效应是生态系统 (斑块 )边缘和生态过渡区所呈现出的生态效应。但由于景观性质、研究目标和斑块形状的变化 ,边缘效应影响的范围和程度差异较大。核心斑块与周边景观之间的相似性既可以增强边缘效应 ,也可以减弱边缘效应。正确理解和确定边缘效应的影响范围和程度直接关系到对野外环境观测数据的科学使用。许多情况下 ,由于未能正确认识一个生态系统(斑块 )的边缘效应 ,时常会将在边缘效应地区获得的数据与系统内部核心区的观测数据混淆使用 ,得出一些不科学的结论。边缘效应的定量评价对于进行科学的野外环境观测 ,及其在自然保护区功能区设计和生物多样性保护中具有重要意义。但如何定量评价生态系统 (斑块 )的边缘效应目前还缺乏科学有效的方法。从分析边缘效应的概念和影响因子出发 ,结合地理信息系统 ,提出了开展定量评价斑块边缘效应的方法 ,并探讨了定量研究边缘效应的生态学意义。     

Climatic change and its ecological implications at a subantarctic island

Summary Marion Island (47°S, 38°E) has one of the most oceanic climates on earth, with consistently low air temperatures, high precipitation, constantly high humidity, and low incident radiation. Since 1968 mean surface air temperature has increased significantly, by 0.025° C year^–1. This was strongly associated with corresponding changes in sea surface temperature but only weakly, or not at all, with variations in radiation and precipitation. We suggest that changing sealevel (atmospheric and oceanic) circulation patterns in the region underlie all of these changes. Sub-Antarctic terrestrial ecosystems are characterized by being species-poor and having a simple trophic structure. Marion Island is no exception and a scenario is presented of the implications of climatic change for the structure and functioning of its ecosystem. Primary production on the island is high and consequently the vegetation has a large annual requirement for nutrients. There are no macroherbivores and even the insects play only a small role as herbivores, so most of the energy and nutrients incorporated in primary production go through a detritus, rather than grazing, cycle. Ameliorating temperatures and increasing CO₂ levels are expected to increase productivity and nutrient demand even further. However, most of the plant communities occur on soils which have especially low available levels of nutrients and nutrient mineralization from organic reserves is the main bottleneck in nutrient cycling and primary production. Increasing temperatures will not significantly enhance microbially-mediated mineralization rates since soil microbiological processes on the island are strongly limited by waterlogging, rather than by temperature. The island supports large numbers of soil macro-arthropods, which are responsible for most of the nutrient release from peat and litter. The activities of these animals are strongly temperature dependent and increasing temperature will result in enhanced nutrient availability, allowing the potential for increased primary production due to elevated temperature and CO₂ levels to be realized. However, housemice occur on the island and have an important influence on the ecosystem, mainly by feeding on soil invertebrates. The mouse population is strongly temperature-limited and appears to be increasing, possibly as a result of ameliorating temperatures. We suggest that an increasing mouse population, through enhanced predation pressure on soil invertebrates, will decrease overall rates of nutrient cycling and cause imbalances between primary production and decomposition. This, along with more direct effects of mice (e.g. granivory) has important implications for vegetation succession and ecosystem structure and functioning on the island. Some of these are already apparent from comparisons with nearby Prince Edward Island where mice do not occur. Other implications of climatic change for the island are presented which emphasize the very marked influences that invasive organisms have on ecosystem structure and functioning. We suggest that changing sealevel circulation patterns, by allowing opportunities for colonization by new biota, may have an even more important influence on terrestrial sub-Antarctic ecosystems than is suggested merely on the basis of associated changes in temperature or precipitation.     

Perchlorate and halophilic prokaryotes: implications for possible halophilic life on Mars

In view of the finding of perchlorate among the salts detected by the Phoenix Lander on Mars, we investigated the relationships of halophilic heterotrophic microorganisms (archaea of the family Halobacteriaceae and the bacterium Halomonas elongata) toward perchlorate. All strains tested grew well in NaCl-based media containing 0.4 M perchlorate, but at the highest perchlorate concentrations, tested cells were swollen or distorted. Some species (Haloferax mediterranei, Haloferax denitrificans, Haloferax gibbonsii, Haloarcula marismortui, Haloarcula vallismortis) could use perchlorate as an electron acceptor for anaerobic growth. Although perchlorate is highly oxidizing, its presence at a concentration of 0.2 M for up to 2 weeks did not negatively affect the ability of a yeast extract-based medium to support growth of the archaeon Halobacterium salinarum. These findings show that presence of perchlorate among the salts on Mars does not preclude the possibility of halophilic life. If indeed the liquid brines that may exist on Mars are inhabited by salt-requiring or salt-tolerant microorganisms similar to the halophiles on Earth, presence of perchlorate may even be stimulatory when it can serve as an electron acceptor for respiratory activity in the anaerobic Martian environment.     

生态环境需水量研究进展与理论探析

通过对国内外生态环境需水量研究现状的分析 ,阐述了生态环境需水量的概念。提出生态环境需水量是由河道内生态环境需水和河道外生态环境需水、景观娱乐需水三部分组成的观点 ,从生态环境需水的时空分布、自然生态优先和可持续角度对其内涵进行了探讨 ,分析了生态环境需水量的动态性、可控制性和极限特性。对目前采取的各种生态环境需水量计算评价方法进行了总结 ,展望了该研究领域的发展趋势。     

大优角蚱卵块外型的数学模型研究及其生态学意义

【目的】探究大优角蚱Eucriotettix grandis独特的卵块形态的生态学意义。【方法】在大量野外调查大优角蚱卵块生态学特征的基础上, 通过对卵块图片的三维数据点进行截面线抽取, 获得卵块截面曲线的拟合方程, 并用线条拟合法建立相应的数学模型。依据拟合曲线的曲率图和二阶导数值图对数据拟合曲线的几何特性进行分析。【结果】大优角蚱多以完整卵块的形式产卵, 卵块为约六边形的橘子瓣状结构, 且卵块顶部有一明显的半球形凹槽, 底部则中间略隆起。利用线条拟合理论, 构造出既能够有效满足拟合优度, 又能够满足光滑度的核函数, 通过对函数取值得到模型曲线非常近似拟合于真值曲线。【结论】凹槽很可能是便于存水, 保持卵块的湿润, 利于卵的存活和孵化; 棱角有利于缓解卵块的远距离滚动和破散, 紧密结合的卵块结构利于卵的保温保湿。     

Widespread N-acetyl-D-glucosamine uptake among pelagic marine bacteria and its ecological implications

Dissolved free and combined N-acetyl-D-glucosamine (NAG) is among the largest pools of amino sugars in the ocean. NAG is a main structural component in chitin and a substantial constituent of bacterial peptidoglycan and lipopolysaccharides. We studied the distribution and kinetics of NAG uptake by the phosphoenolpyruvate:NAG phosphotransferase systems (PTS) in marine bacterial isolates and natural bacterial assemblages in near-shore waters. Of 78 bacterial isolates examined, 60 took up 3H-NAG, while 18 showed no uptake. No systematic pattern in NAG uptake capability relative to phylogenetic affiliation was found, except that all isolates within Vibrionaceae took up NAG. Among 12 isolates, some showed large differences in the relationship between polymer hydrolysis (measured as chitobiase activity) and uptake of the NAG, the hydrolysis product. Pool turnover time and estimated maximum ambient concentration of dissolved NAG in samples off Scripps Pier (La Jolla, Calif.) were 5.9 +/- 3.0 days (n = 10) and 5.2 +/- 0.9 nM (n = 3), respectively. Carbohydrate competition experiments indicated that glucose, glucosamine, mannose, and fructose were taken up by the same system as NAG. Sensitivity to the antibiotic and NAG structural analog streptozotocin (STZ) was developed into a culture-independent approach, which demonstrated that approximately one-third of bacteria in natural marine assemblages that were synthesizing DNA took up NAG. Isolates possessing a NAG PTS system were found to be predominantly facultative anaerobes. These results suggest the hypothesis that a substantial fraction of bacteria in natural pelagic assemblages are facultative anaerobes. The adaptive value of fermentative metabolism in the pelagic environment is potentially significant, e.g., to bacteria colonizing microenvironments such as marine snow that may experience periodic O2-limitation.     

Winter sediment resuspension in McMurdo Sound,Antarctica, and its ecological implications

Summary Sediment resuspension is a common phenomenon whose importance may be magnified in nearshore environments surrounding Antarctica, especially during the austral winter. Analyses suggest that sediments in the vicinity of McMurdo Station contain viable algal material throughout this period of darkness. The resuspension of these sediments, shown by sediment trap collections and underwater observations, would introduce organics into the water column and may provide an alternative food source for planktonic herbivores inhabiting near-shore environments during the Antarctic winter.     

The determination of nucleic acids in freshwater plankton and its ecological implications *

Nucleic acid concentrations show large variations between different planktonic species. RNA concentration is much higher in phytoplankton than in zooplankton. DNA varies to a considerable extent, being five to six times higher in copepods than in cladocerans. In Daphnia hyalina, nucleic acid contents are proportional to dry weight during the whole life cycle except in newborn Daphnia where DNA concentration is abnormally high. Seasonal variations affect, to a large extent, nucleic acid concentrations. These results rule out the possibility of using nucleic acids as indicators of biomass in mixed planktonic populations.     

基于ESTDA模型的中国水生态足迹及水生态压力评价

基于水足迹视角,测度了中国31个省份2000-2018年的水生态足迹广度、深度及水生态压力,采用ESTDA框架对其时空动态特征进行分析。结果表明：①研究期内,中国水生态足迹总量呈波动上升态势;水生态承载力波动幅度较大,空间分布格局整体呈现自东南向西北逐渐较少的趋势。②水生态足迹广度与水生态承载力呈同步变化趋势,整体上已接近水资源可提供的流量资本上限,各省市水生态足迹深度差异较大。③研究期内,水生态压力指数小于1的区域与水生态足迹深度为1的区域相吻合,水生态压力指数大于1的区域主要分布在华北及西北地区。④LISA时间路径表明,水生态足迹广度、深度及水生态压力的整体空间格局均具有较强的稳定性;三者的局部空间结构在空间依赖方向上的稳定性依次加强;空间格局演化的空间整合性呈现水生态足迹深度 > 水生态压力 > 水生态足迹广度,空间上,水生态足迹广度正向协同增长省份主要集中于南方省份,而水生态足迹深度和水生态压力正向协同增长区则分布于华北、西北地区;各要素的空间分布格局表现出较强的路径依赖及锁定特征。     

From shallow to deep water: an ecological study of the Hirnantia brachiopod Fauna (Late Ordovician) and its global implications

A large brachiopod fauna collected through the upper Wanyaoshu Formation (middle Hirnantian), West Yunnan, China displays, for the first time, a vertical transition within the Hirnantia fauna. The inner to mid-shelf Fardenia–Hirnantia association segues into the deeper water Aegiromena–Anisopleurella association during the Metabolograptus persculptus marine transgression. This transition parallels the pattern apparent in onshore–offshore gradients within the Hirnantian, imitating Walther’s Law for facies, instead predicting the seaward transitions between community types within a single transgressive sequence. In addition, large-sized brachiopods such as Hirnantia and Eostropheodonta become rarer and small-sized brachiopods, for example, Aegiromena and Anisopleurella more common. It is a rare opportunity to view transformations in community composition and structure within the Hirnantia fauna together with changes in both the size of individuals and populations (from large to small) during the transgression.     

捕食风险及其对动物觅食行为的影响

对捕食风险的涵义及其对猎物动物觅食行为的影响、猎物动物面对捕食风险时的反应进行了论述。捕食风险可以简单地理解为一定时间内猎物动物被杀死的概率。当捕食风险存在时 ,动物会选择相对安全但觅食效益较低的地点觅食 ;由于死亡率和消化方面的限制 ,一般都会产生食谱收缩 ;觅食活动方式的时间格局也会因捕食风险而发生改变 ,如水生动物的昼夜垂直迁移、某些陆生动物昼行性与夜行性活动的转换、月光回避等。在与捕食者发生遭遇时 ,猎物动物的主要反应是 :①发出某些信号以阻止捕食者的追捕 ;②靠近并注视捕食者 ;③逃逸 ;④在一定的时间恢复觅食活动。在以往的研究中 ,对捕食者种类已经有了较多的了解 ,而对猎物如何判断捕食者丰富度信息、估计风险程度等方面则知之甚少 ;同时 ,对捕食风险水平的调控、对多种因素的综合分析也较少涉及。在今后的研究中 ,还应该考虑研究的尺度问题 ,因为在不同尺度的环境条件下 ,猎物动物对于捕食风险的反应可能大相径庭。     

Post‐weaning ontogeny of the mandible in fossorial water voles: ecological and evolutionary implications

Ventura, J. and Casado‐Cruz, M. 2011. Post‐weaning ontogeny of the mandible in fossorial water voles: ecological and evolutionary implications. —Acta Zoologica (Stockholm) 92 : 12–20. Geometric morphometrics was applied to the mandible of fossorial water voles (Arvicola terrestris monticola) to determine size and shape variations in this structure during post‐weaning ontogeny. The sample consisted of collection specimens obtained in the Aran Valley (Spain), which were grouped into six age classes. Mandible size and shape did not differ significantly between sexes, but between age classes. Mandible size accounted significantly for the shape variation. After the size‐related differences were removed, the mandible shape did not show significant sexual dimorphism but differences by age remained significant. The main shape changes occur between the third and tenth weeks of life and are related to the shift from suckling to a herbivorous diet. Although mandible shape was less remodelled after that age, an appreciable variation also occurs during adulthood. Age‐related changes lead to enhancing the digging potential of the mandible, which in adults becomes a robust structure with an increased surface and stronger crests for muscle insertion. As part of the mandible shape variation was not related to the size‐dependent adjustment and diet does not vary significantly between juvenile and adult voles, shape changes that occur during adulthood can be related to the mechanical stress derived from digging activities.