Divergence in style length and pollen size leads to a postmating‐prezygotic reproductive barrier among populations of Silene latifolia

A central tenet of speciation research is the need to identify reproductive isolating barriers. One approach to this line of research is to identify the phenotypes that lead to reproductive isolation. Several studies on flowering plants have shown that differences in style length contribute to reproductive isolation between species, leading us to consider whether style length could act as a reproductive barrier among populations of a single species. This could occur if style length varied sufficiently and pollen size covaried with style length. Populations of Silene latifolia exhibit variation in flower size, including style length, that is negatively correlated with annual precipitation. We show that this divergence in style length has a genetic basis and acts as a reproductive barrier: males from small‐flowered populations produced relatively small pollen grains that were poor at fertilizing ovules when crossed to females from large‐flowered populations, leading to a significant reduction in seed production. Manipulating the distance pollen tubes had to travel revealed that this failure was purely mechanical and not the result of other incompatibilities. These results show that style length acts as a postmating‐prezygotic reproductive barrier and indicate a potential link between ecotypic differentiation and reproductive isolation within a species.     

The point of a Guillemot's egg

The adaptive significance of avian egg shape in birds is poorly understood. The pyriform (pear‐like) shape of the Common Guillemot's Uria aalge egg has long been considered to be an adaptation to prevent eggs rolling off the bare cliff ledges on which this species breeds. Rolling was thought to be prevented either by the egg spinning like a top, which is not the case, or by rolling in an arc, which it does but with little influence on whether the egg will fall from a ledge. We therefore sought alternative explanations for the pyriform shape of the Common Guillemot's egg. This species breeds in extremely dense colonies, which makes their eggs vulnerable to mechanical damage from conspecifics, and to contamination by debris such as faeces and soil. We present evidence consistent with both these possible explanations. First, the pyriform shape of Common Guillemot eggs means that a higher proportion of the eggshell lies in contact with the substrate and this may minimize the effect of impacts. Resistance to impacts may be further enhanced because their eggshells are especially thick where they are in contact with the substrate. Secondly, Common Guillemot eggs are often heavily contaminated with faecal material and other debris during incubation. Most contamination is on the pointed end of the egg where it is in contact with the substrate; the pyriform shape thus keeps the blunt end of the egg, which has the highest porosity, relatively free of contamination, which in turn may facilitate both gas exchange during incubation and the hatching process, because the chick emerges from the blunt end of the egg.     

陕北榆林王阳畔遗址的植硅体分析

榆林地处农牧交错带,是研究环境演变和人地关系的理想地区。本文基于植硅体分析,探讨了该地区王阳畔遗址仰韶晚期至龙山早期过渡阶段的农业生产情况及农业对环境的适应等。遗址剖面及灰坑样品的植硅体分析表明:仰韶晚期,粟和黍是先民的主要粮食作物,而黍较粟始终保持着种植优势;龙山早期,粟作农业逐渐衰落。植硅体组合图谱显示,先民在此遗址活动期间,气候是略偏凉偏干的,整体上较为稳定,呈现出干凉化的趋势。综合来看,农业活动的强弱在一定程度上响应了环境的变化。需要指出的是,该遗址榆科植硅体的大量发现,不仅补充了史前植物利用史,同时也对丰富植硅体数据库具有重要意义。     

Ultrastructure of Pollen Grains from Forced and Unforced Shrubs of Common Lilac

Forcing makes possible to induce plant flowering independently of the season. In lilac, high temperature is the factor that breaks deep dormancy. The deepest dormancy occurs between the end of October and the end of December. Depending on the depth of dormancy, the starting temperatures required for forcing are 37°C in November, 31°C in December, and 25°C in January–March. Under natural conditions, the temperature inducing the inflorescence bud breaking is 6°C, whereas 9°C and 13°C or more allow inflorescence elongation and flowering, respectively (Kronenberg, 1994). In the present work, the effect of high temperature at the beginning of the forcing cycle on the structure of developing pollen grains of common lilac was investigated. Pollen grains from the outdoor-grown (control) shrubs showed no signs of degeneration. They were spherical, three-colpate to colporoidate, and bicellular, and contained large numbers of lipid bodies. High temperatures at the early forcing cycle (November) resulted in the degeneration of most microspores. The first signs of degeneration (cytoplasm plasmolysis) were observed at the tetrad stage and in mature anthers; the microspores consisted only of the outer and inner sporopolenin layers.     

农田周围生态保留带中普通田鼠的种群生态学：种群数量动态及结构

于2003年5月~2004年11月,采用标志重捕法对栖息在生态保留带的普通田鼠种群结构和数量动态进行了跟踪研究。结果表明,两年中种群密度夏季最大分别达到410个体/hm2和641个体/hm2,春季最少分别达到166个体/hm2和153个体/hm2,种群数量从7月份开始增长,8月份种群密度减少并于11月份开始重新增长。种群中雌性个体数量比较多,雌性在种群中的居留时间较长,同时存活率比雄性高,这导致种群数量的季节变化。种群周转率比较高,在两个捕鼠期间种群中的80%个体被更新,这表明普通田鼠在生态保留带中的活动非常频繁,不断与周围的其他种群进行交流,提高了种群对环境的适应能力。种群中雌雄个体的巢区之间没有年间变化,活动巢区比较小,巢区长度2003年平均为11 m,最长为37.5 m,2004年平均为13 m,最长为52 m。Pearson相关指数表明种群数量和生态保留带年龄、覆盖率和高度之间没有相关性。     

中国林蛙蝌蚪和大蟾蜍蝌蚪的最适温度、逃避温度及致死温度

报道了中国林蛙蝌蚪 (Ranachensinensis)和大蟾蜍蝌蚪 (Bufogargarizans)在不同驯化温度下的最适温度、逃避温度和致死温度的研究结果。将中国林蛙蝌蚪和大蟾蜍蝌蚪分别在 5、1 5和 2 5℃ 3个不同温度下驯养 3周 ,利用温度梯度装置观察记录 2种蝌蚪的最适温度、逃避温度和最高致死温度。结果表明 ,经过在 5、1 5和 2 5℃ 3个温度下的驯化 ,中国林蛙蝌蚪的最适温度范围分别为 1 3 . 5～ 1 8℃、2 0. 5～2 5℃和 2 3～ 2 7. 5℃ ;大蟾蜍蝌蚪的最适温度范围分别为 1 2～ 1 6 .5℃、2 1～ 2 5. 5℃和 2 2～ 2 6. 5℃。中国林蛙蝌蚪和大蟾蜍蝌蚪的最高致死温均在 3 7～ 3 8℃之间 ,最低致死温均为 0℃。驯化温度对最适温度影响显著 (P <0 .0 1 ) ,对致死温度则没有显著影响。驯化温度对中国林蛙蝌蚪和大蟾蜍蝌蚪的逃避温度产生的影响比最适温度的大。     

斯洛维尼亚池塘中大蟾蜍的交配模式

为了解大蟾蜍( Bufo bufo)的配对成功是否与身体大小有关,在蟾蜍产卵之前,我们在斯洛文尼亚捕捉和测量了2 224只成体样本。在这些捕获的个体中, 1 772只为雄性, 452只为雌性,其中355对处于抱对状态。雌性的体长(从吻端到泄殖腔的距离)一般比雄性稍长。无论雄性还是雌性,抱对者的体长均大于未抱对者。抱对的雄性和雌性的体长具有显著的正相关。我们所发现的大小匹配的交配模式,与从其它普通蟾蜍种群得到的结果一致[动物学报51 (3) : 513 -515 , 2005]。     

Variation partitioning for range expansion of an introduced species: the common waxbill Estrilda astrild in Portugal

The common waxbill Estrilda astrild was first introduced to Portugal, from Africa, in 1964, from where it has spread to much of the country and to Spain. We modelled the expansion of this species on a 20×20-km UTM grid in 4-year periods from 1964 to 1999. Colonisation process on a grid was modelled as a function of several biophysical and spatio-temporal variables through the fitting of several multiple logistic equations. Variation partitioning confirmed the importance of the spatial-temporal component, explaining 33% of the total variation, followed by the combined effects of both environmental and spatial-temporal variables (around 25%). Only 11% of the total variation can be attributed strictly to the considered environmental factors.     

Phenolic compound localisation in <Emphasis Type="Italic">Polypodium vulgare</Emphasis> L. rhizomes after mannitol-induced dehydration and controlled desiccation

Polypodium vulgare L. is a desiccation-tolerant fern that can withstand successive dry periods in its life cycle. To better understand this mechanism, the current study was undertaken to assess the role of phenolic compounds in rhizome dehydration and determine their localisation in the rhizome cells after enforced dehydration in mannitol solution or controlled desiccation with or without abscisic acid (ABA) pretreatment. Phenolic distribution at the subcellular level was studied using gold particle-complexed laccase. Cells from different tissues: cortical parenchyma, endodermis and stelar elements--pericycle, sieve cells and vascular parenchyma were observed under a transmission electron microscope (TEM). The content of phenolic compounds was greater in ABA-untreated rhizomes after enforced dehydration in mannitol solution and subsequent rehydration. After controlled desiccation the phenolic content significantly increased in ABA-untreated rhizomes. A large number of phenolic compound deposits were present in all types of rhizomatous cells. Phenolics were widely distributed in the vacuoles of all cells, and in the secondary cell walls of sieve cells, although scattered labelling was hardly ever observed in the primary cell walls. In dehydrated and plasmolysed cells from the cortex and endodermis, phenolic compounds were present in the apoplastic compartments between the plasma membranes and the cell walls. There is evidence that abscisic acid plays a role as a crucial antioxidant resulting in no damage and a lower level of phenolic increase as compared to ABA-untreated rhizomes. Moreover, the location of phenolics suggests a protective chemical barrier against environmental stresses.