Ecological differentiation and diploid superiority across a moving ploidy contact zone

Plant polyploid complexes provide useful model systems for distinguishing between adaptive and nonadaptive causes of parapatric distributions in closely related lineages. Polyploidy often gives rise to morphological and physiological changes, which may be adaptive to different environments, but separate distributions may also be maintained by reproductive interference caused by postzygotic reproductive isolation. Here, we test the hypothesis that diploid and descendent polyploid races of the wind-pollinated herb Mercurialis annua , which are found in parapatry over an environmental gradient in northeast Spain, are differentiated in their ecophysiology and life history. We also ask whether any such differences represent adaptations to their different natural environments. On the basis of a series of reciprocal transplant experiments in the field, and experiments under controlled conditions, we found that diploid and polyploid populations of M. annua are ecologically differentiated, but that they do not show local adaptation; rather, the diploids have higher fitness than the polyploids across both diploid- and polyploid-occupied regions. In fact, diploids are currently displacing polyploids by advancing south on two separate fronts in Spain, and previous work has shown that this displacement is being driven to a large extent by asymmetrical pollen swamping. Our results here suggest that ecophysiological superiority of the diploids may also be contributing to their expansion.     

贻贝棘尾虫(原生动物,纤毛门)镜像骈体自身各部移接的实验

棘尾虫是细胞表面具有特殊纤毛结构排列方式的复杂下毛类纤毛虫。其镜像骈体的两列纤毛结构几乎完全是左右对称排列 ,一个是正常方式排列的 ,另一个是相反方式排列。本文包括两项移接实验 :1)将棘尾虫口对镜像骈体一侧细胞的后半部分倒转 180°与另一侧细胞的前半部分对接 ;2 )将此种骈体一侧后半部分调转90°与另一侧细胞的前半部分对接。接后定时分期固定接块 ,以蛋白银染色法 ,观察其发育过程及结果。实验 1的发育结果为有的仍形成口对镜像骈体 ;有的成为末端对末端的镜像骈体。实验 2的发育结果为全部成为口对镜像骈体。两项实验结果均可用位置值假说解释 ,实验 1属于位置值插入的结果 ;实验 2为位置值添加的结果。为何实验Ⅰ有的发育成口对镜像骈体有的发育成末端对末端的镜像骈体 ,而实验 2却全部发育成口对镜像骈体呢 ?这是接块发育中是否发生对折的结果。Shietal.(1991)认为与预存的缘棘毛和是否具有完整表膜的面积大小有关系。接块在发育中是否发生对折与接块的伤口一侧面积大小和具完整表膜有关系。接块具完整表膜和缘棘毛的一侧由于新缘棘毛和口围带的发育生长 ,造成该侧的伸张 ,产生前后两接块向伤口一侧对折的压力 ,从而接块发生对折形成口对镜像骈体。我们认为还应有其它因素 :(1)与细胞     

机械措施控制加拿大萨斯克彻温草场丛生卷柏生长的经济分析

对加拿大萨斯克彻温省干旱棕色土壤带、湿润棕色土壤带及黑棕色土壤带上的沙土和壤土草场区所应用的挖鱼鳞坑和犁翻两种机械措施控制丛生卷柏侵蚀天然草场的效果进行了经济效益分析。分析结果表明 :当市场折扣率为 8%和 10 %时 ,犁翻处理在任何草场区实施均在 2 0 a内不能收回投入 ,说明该处理在经济上是不可行的 ;而挖鱼鳞坑在黑棕色土壤带实施分别需要10 a和 11a才能收回投入 ,在湿润棕色土壤带分别需 12 a和 14 a,而在干燥棕色土壤带则分别需 15 a和 2 2 a。但在实际中 ,这两种处理是否能发挥 2 0 a以上的经济效益还需进一步研究。草场管理者应根据两种处理控制丛生卷柏效果及饲草产量的增量来确定净现值和内部报酬率 ,估测收回投入的年限 ,最终作出合理的经济决策。当然 ,如果考虑到铲除丛生卷柏所带来的一些生态方面的争议 ,草场管理者应慎重考虑其他一些改良措施 ,如改进放牧管理 ,施化肥及播种目标草种等 ,以达到取得经济效益的目的     

Genital lock-and-key system and premating isolation by mate preference in carabid beetles (Carabus subgenus Ohomopterus)

The shapes and lengths of copulatory pieces and vaginal appendices of the carabid beetle subgenus Ohomopterus (genus Carabus) vary among species. In Japan, the species in the group with a medium body size (C. yaconinus, C. iwawakianus, C. maiyasanus, C. uenoi, C. arrowianus, C. esakii, and C. insulicola) are usually allopatric or parapatric, except at Mt Kongosan, where C. uenoi, C. iwawakianus, and C. yaconinus are sympatrically distributed. The degree of premating isolation by mate preference was high between sympatric populations, irrespective of the genetic distance between them. However, premating isolation was absent between parapatric populations. The degree of premating isolation for allopatric populations spanned a wide range of isolation values. Thus, mate discrimination by males seems to have evolved mostly between sympatric pairs. These results suggest two hypotheses. First, premating isolation has evolved through reinforcement or through reproductive character displacement after sympatric contact. Second, premating isolation has evolved in allopatry, and as a result of premating isolation, the species can coexist in sympatry. We also examined the degree of mechanical isolation between C. uenoi and C. iwawakianus (a sympatric pair), which have a very large difference in the length of the copulatory piece. The insertion success was low and only one female produced viable offspring among 15 crosses; however, death in females due to copulation was rare. For sympatric matings between C. uenoi and C. iwawakianus, a large difference in the genital size might reduce the gene flow with small mating costs. Gene flow that was significantly reduced by genital difference might cause either the evolution of premating isolation through reinforcement/reproductive character displacement or through the maintenance of a high degree of premating isolation following sympatric contact. © 2006 The Linnean Society of London, Biological Journal of the Linnean Society, 2006, 87 , 145–154.     

A cohesion/tension model for the gating of aquaporins allows estimation of water channel pore volumes in Chara

The water permeability (hydraulic conductivity; Lp) of turgid, intact internodes of Chara corallina decreased exponentially as the concentration of osmolytes applied in the medium increased. Membranes were permeable to osmolytes and therefore they could be applied on both sides of the plasma membrane at concentrations of up to 2.0 m (5.0 MPa of osmotic pressure). Organic solutes of different molecular size (molecular weight, MW) and reflection coefficients (σ_s) were used [heavy water HDO, MW: 19, σ_s: 0.004; acetone, MW: 58, σ_s: 0.15; dimethyl formamide (DMF), MW: 73, σ_s: 0.76; ethylene glycol monomethyl ether (EGMME), MW: 76, σ_s: 0.59; diethylene glycol monomethyl ether (DEGMME), MW: 120, σ_s: 0.78 and triethylene glycol monoethyl ether (TEGMEE), MW: 178, σ_s: 0.80]. The larger the molecular size of the osmolyte, the more efficient it was in reducing cell Lp at a given concentration. The residual cell Lp decreased with increasing size of osmolytes. The findings are in agreement with a cohesion/tension model of the osmotic dehydration of water channels (aquaporins; AQPs), which predicts both reversible exponential dehydration curves and the dependence on the size of osmolytes which are more or less excluded from AQPs (Ye, Wiera & Steudle, Journal of Experimental Botany 55, 449–461, 2004). In the presence of big osmolytes, dehydration curves were best described by the sum of two exponentials (as predicted from the theory in the presence of two different types of AQPs with differing pore diameters and volumes). AQPs with big diameters could not be closed in the presence of osmolytes of small molecular size, even at very high concentrations. The cohesion/tension theory allowed pore volumes of AQPs to be evaluated, which was 2.3 ± 0.2 nm³ for the narrow pore and between 5.5 ± 0.8 and 6.1 ± 0.8 nm³ for the wider pores. The existence of different types of pores was also evident from differences in the residual Lp. Alternatively, pore volumes were estimated from ratios between osmotic (P_f) and diffusional (P_d) water flow, yielding the number of water molecules (N) in the pores. N-values ranged between 35 and 60, which referred to volumes of 0.51 and 0.88 nm³/pore. Values of pore volumes obtained by either method were bigger than those reported in the literature for other AQPs. Absolute values of pore volumes and differences obtained by the two methods are discussed in terms of an inclusion of mouth parts of AQPs during osmotic dehydration. It is concluded that the mouth part contributed to the absolute values of pore volumes depending on the size of osmolytes. However, this can not explain the finding of the existence of two different types or groups of AQPs in the plasma membrane of Chara.     

西花蓟马取食与机械损伤对菜豆叶片抗氧化系统的影响

本文研究了西花蓟马Frankliniella occidentalis(Pergande)取食和机械损伤诱导对菜豆抗氧化系统的影响,比较了不同损伤形式诱导的抗氧化酶活力和抗氧化物质含量的变化差异。结果表明,西花蓟马取食和机械损伤均可诱导菜豆叶片内过氧化物酶(POD)、超氧化物歧化酶(SOD)和过氧化氢酶(CAT)3种抗氧化酶活性有不同程度的升高,但两种处理诱导的抗氧化酶活性变化规律不完全相同,各种酶活性达到最高点时间不同,西花蓟马取食对抗氧化酶活力的诱导作用大于机械损伤的。两种处理诱导下的类胡萝卜素的含量变化不大,但不论西花蓟马取食还是机械损伤均导致菜豆叶片内类黄酮和总酚含量整体呈下降趋势,西花蓟马的取食诱导的下降幅度大于机械损伤的。因此,西花蓟马取食诱导明显高于机械损伤对菜豆抗氧化系统的影响。     

Mechanical properties of lipid bilayers and regulation of mechanosensitive function

Material properties of lipid bilayers, including thickness, intrinsic curvature and compressibility regulate the function of mechanosensitive (MS) channels. This regulation is dependent on phospholipid composition, lateral packing and organization within the membrane. Therefore, a more complete framework to understand the functioning of MS channels requires insights into bilayer structure, thermodynamics and phospholipid structure, as well as lipid-protein interactions. Phospholipids and MS channels interact with each other mainly through electrostatic forces and hydrophobic matching, which are also crucial for antimicrobial peptides. They are excellent models for studying the formation and stabilization of membrane pores. Importantly, they perform equivalent responses as MS channels: (1) tilting in response to tension and (2) dissipation of osmotic gradients. Lessons learned from pore forming peptides could enrich our knowledge of mechanisms of action and evolution of these channels. Here, the current state of the art is presented and general principles of membrane regulation of mechanosensitive function are discussed.     

冷冻液温和季节对鼠尾过冷点的影响

为研究动物对寒冷的适应性,将鼠尾置于冷液浸冻,发现在一定条件下鼠尾组织可发生过冷现象。实验表明,鼠尾组织的过冷点和冷冻液温有关,同一季节冷冻液温越低过冷点越高;而不同季节相同冷冻条件下,冬季鼠尾组织的过冷点明显低于春季。 动物肢体组织的过冷特性是动物的抗寒冷特性,它和组织自身的物理化学性质有关。理沦证明,过冷度(△T)和表面张力(O)、摩尔质量(M),冰点(Ti)、密度(p)、摩尔凝固热(△H)及冰胚临界半径(rk)有关,其关系式为△T=26MTi/p△Hrk.     

Water Striders:The Biomechanics of Water Locomotion and Functional Morphology of the Hydrophobic Surface(Insecta:Hemiptera-Heteroptera)

Water striders are insects living on the water surface, over which they can move very quickly and rarely get wetted. We measured the force of free walking in water striders, using a hair attached to their backs and a 3D strain gauge. The error was calculated by comparing force and data derived from geometry and was estimated as 13%. Females on average were stronger (1.32 mN) than males (0.87 mN), however, the ratio of force to weight was not significantly different. Compared with other lighter species, Aquarius paludum seems stronger, but the ratio of force to weight is actually lower. A. paludum applies about 0.3 mN·cm-1 to 0.4 mN·cm-1 with its mid-legs, thus avoiding penetrating the surface tension layer while propelling itself rapidly over the water surface.We also investigated the external morphology with SEM. The body is covered by effectively two layers of macro-and micro-hairs, which renders them hydrophobic. The setae are long (40 um-60 um) and stiff, being responsible for waterproofing, and the microtrichia are much smaller (<10 um), slender, and flexible, holding a bubble over the body when submerged.