The use and function of snake skins in the nests of Great Reed Warblers Acrocephalus arundinaceus

We documented and experimentally tested the use of snake skins in construction of nests in a Great Reed Warbler Acrocephalus arundinaceus population in southwestern Slovakia. There was no difference in predation rates of artificial nests that did or did not contain sloughs. We suggest that snake skins in Great Reed Warbler nests may serve as a post‐pairing signal revealing female parental quality.     

Enzymes of snake venoms

Snakes' venom is a mixture of biologically active substances, containing proteins and peptides. A number of these proteins interact with haemostasis system components. Activators and inhibitors affecting blood coagulation and fibrinolysis systems are of special interest. Venom components can be classified into three main groups, such as procoagulants, anticoagulants and fibrinolytic enzymes according to their action. This review is focused on enzymes from Agkistrodon halys halys venom. They are thrombine-like enzyme, named Ancystron-H, flbrinogenolytic enzyme, protein C activator and platelet aggregation inhibitor. Ancystron-H is used for determination of fibrinogen level in blood plasma of patients undergoing heparin treatment and blood coagulation inhibitors accumulation. The fibrinogenolytic enzyme can be used as the instrument for protein-protein interactions in fibrinogen-fibrin system. The protein C activator is used for protein C level determination in blood plasma with different pathologies. Functions of the platelet aggregation inhibitor, belonging to disintegrins group, can be used for development of antithrombotic preparations. Information about the use of snake venoms in science and medicine is presented.     

Pseudo-cholinesterase of snake sera

• 1.1. Pseudo-cholinesterase (EC 3.1.1.8), enzyme activity was detected in sera of Elapid (Bungarus fasciatus) and Colub (Pytas korros) snakes and found to be higher in P. korros.
• 2.2. There were no significant seasonal or sex variations in the cholinesterase activity in the sera of the two species.
• 3.3. The P. korros enzyme obeyed Michaelis-Menten kinetics, with K_m = 4.55 mM; that of B. fasciatus changed only slightly with increases in substrate concentration.

     

Cytoskeletal rearrangements in human red blood cells induced by snake venoms: light microscopy of shapes and NMR studies of membrane function

RBCs (red blood cells) circulating through narrow blood capillaries withstand major deformation. The mechanical and chemical stresses commonly exerted on RBCs continue to attract interest for the study of membrane structure and function. Snake venoms are lethal biochemical 'cocktails' that often contain haemotoxins, metalloproteinases, myotoxins, neurotoxins, phosphodiesterases, phospholipases and proteases. We have monitored the effects of 4 snake venoms (Pseudechis guttatus, Oxyuranus scutellatus, Notechis scutatus and Naja kaouthia) on human RBCs using NMR spectroscopy, DIC (differential interference contrast) and confocal light microscopy. RBCs underwent reproducible stomatocytosis, with unusual geographical-like indentations, spherocytosis, followed by rapid lysis. Confocal micrographs using a fluorescent dye linked to phalloidin showed that the change in morphology was associated with the aggregation of actin in the cytoskeleton. (31)P NMR saturation transfer experiments recorded transport of the univalent anion HPA (hypophosphite) on a subsecond time scale, thereby reporting on the function of capnophorin or Band 3 linked to the cytoskeleton; anion-exchange activity was substantially reduced by venom treatment. We propose a molecular-cytological hypothesis for the shape and functional changes that is different from, or supplementary to, the more 'traditional' bilayer-couple hypothesis more often used to account for similar morphological changes invoked by other reagents.     

蛇神经毒素的研究进展

蛇毒是由许多种蛋白质、多肽、酶类以及其他小分子物质组成的混合物.在蛇毒中已经分离了许多种毒素分子,其中有一大类分子对哺乳动物的神经系统具有毒性效应,习惯上把这类分子成为蛇神经毒素.蛇神经毒素根据其作用位点的不同可以分为四大类:突触前蛇神经毒素、突触后蛇神经毒素、抗胆碱酯酶的蛇神经毒素和离子通道蛇神经毒素.许多蛇神经毒素已经分离纯化并进行了结构与功能的研究,几十近百种蛇神经毒素一级结构和空间结构已经得到测定.近几年来一些蛇神经毒素的基因文库以及cDNA文库已经构建出来,从中分离出的基因已经用于重组蛇神经毒素的生产研究.蛇神经毒素的分子结构与其功能具有较好的对应关系,即作用机制相同的毒素具有类似的空间结构.天然的蛇神经毒素以及重组的蛇神经毒素都已广泛应用于理论研究和一些临床应用.分离新的蛇神经毒素及其基因以及根据需要设计新的蛇神经毒素分子已成为该领域的热点,采用生物工程的方法规模生产蛇神经毒素也是当前及今后的研究方向.     

Mechanical behaviour of snake skin

Forty-nine samples of skin from the mid-ventral, ventrolateral and mid-dorsal regions of six species of snakes were mechanically tested in uniaxial extension at 0.05 strain/sec. The species of snakes studied ranged from generalists to specialists for arboreal or aquatic habitats. Analysis of the loading curves revealed substantial variation in loads and maximum stiffnesses among samples from different dorsoventral regions within an individual and among homologous samples from different species. Skin thickness varied by a factor of more than five, but this only partially accounts for the differences in the force per width of sample at a given extension. Qualitative differences in the dermal collagen fibres are implied by the shapes of the loading curves and the terminal elastic modulus which varied from about 15 to 585 MN/m². The strain at beginning of failure ranged from 0.12 to 0.60. The size of the scales within a skin sample was not a reliable predictor of the loading behaviour of the sample. Correlations between the mechanical behaviour of skin and specializations in locomotion and associated musculature are discussed.     

Electrophoretic analysis of snake venoms

Electrophoretic analyses were conducted on snake venoms from 21 species representing Elapidae, Crotalidae and Viperidae. Denatured and native venoms were analyzed by polyacrylamide gel electrophoretic (PAGE) methods with sodium dodecyl sulfate (SDS) and without SDS. Both SDS-PAGE and PAGE profiles of venoms from different snake species indicate that some proteins and polypeptide components of these venoms have common electrophoretic characteristics suggesting a genetic relationship. Conversely, the electropherograms also showed the characteristic protein and polypeptide profiles that could differentiate one snake species from another. Therefore, both SDS-PAGE and PAGE profiles suggest that proteins and polypeptides with similar characteristics abound among subspecies or related species, although each venom has a unique profile that differentiates one species from the other.     

Avidity of sera-neutralizing snake venom

Avidity of antivenom sera used for the treatment of snake bites was studied. Sera against the venom of Vipera libetina obtained from producers immunized with crude venoms were more avid than analogous sera obtained to anavenoms. In studying the avidity of polyvalent serum neutralizing the Vipera libetina, echis and cobra venoms showed the serum obtained in immunization with the mixture of crude venoms to be highly avid to all the venoms composing the antigen; besides, it bound the venoms of Vipera libetina and echis more rapidly and more stably than the corresponding monovalent sera.     

具休眠体淡水水生生物分布假说的研究进展

淡水水生生物的分布模式一直是进化和生物地理学研究中的热点问题, 特别是对具休眠体水生生物的研究, 早在达尔文时代就开始探讨具休眠体淡水水生生物分布的原因。根据对文献的整理, 可以将具休眠体淡水水生生物分布模式归纳为三种假说: 随机分布(Everything is Everywhere, EIE)假说、独占(Monopolisation)假说和局域特有(Moderate Endemicity, ME)假说。通过对三种假说的定义, 研究进展和形成不同模式的原因等进行分析, 提出了在研究时需注意是否存在隐存种、季节变化引起基因型变化、研究区域是否覆盖了本物种的所有分布范围、地理环境及地质事件与分布模式之间的关系等问题, 以便更准确的研究具休眠体淡水水生生物分布模式。     

小型哺乳动物种群周期性波动的外因调节假说

对小型哺乳动物种群数量周期性波动的外因调节假说进行介绍 ,概述了食物假说、捕食假说和复合因子假说的主要内容和研究进展。在少数生存环境严酷的小型哺乳动物种群中 ,食物假说能解释它们的周期性数量波动现象 ,可能作为调节因子起作用 ,但难以说明低数量期的确切机制 ,对于大多数小型哺乳动物而言 ,它更可能作为限制因子。捕食假说解释了北欧芬诺斯坎底亚地区某些种群的周期性波动 ,尤其是捕食的间接效应已引起许多学者的关注 ,但也有不支持该假说的证据。对于复合因子假说 ,近年颇受学者重视 ,其中验证食物和捕食交互及累加作用的实验证据较多 ,有的研究还包括气候、种间竞争、空间或社会行为等因素。有关复合因子的实验研究 ,尽管工作是困难和艰巨的 ,花费也是巨大的 ,但所得结果却极有价值 ,为深入理解种群动态调节理论提供了一个合理而有效的手段     

Scale-dependent mechanisms in the population dynamics of an insect herbivore

A multiscale approach has lead to significant advances in the understanding of species population dynamics. The scale-dependent nature of population processes has been particularly clearly illustrated for insect herbivores. However, one of the most well-studied insect herbivores, the galling sawfly Euura lasiolepis, has to date been examined almost exclusively at fine spatial scales. The preference-performance, plant vigour and larval survival hypotheses are well supported by this species. Here, we test these hypotheses at a spatial scale larger than that previously considered, i.e. across a landscape in northern Arizona represented by an altitudinal gradient encompassing a series of drainages. We also develop a qualitative model for understanding the population dynamics of E. lasiolepis based on patterns of survival and mortality found in this study and previous ones. Gall density was highly variable across the altitudinal gradient, not explained by host plant variables, and thus a poor surrogate fot population abundance. These findings for the first time fail to support the plant vigour and preference hierarchy hypotheses for E. lasiolepis. Dispersal limitation most likely explains the lack of support for these hypotheses at this scale. By contrast, sawfly survival, gall abortion, parasitism and larval mortality were well explained by host plant quality variables and altitude. The larval survival hypothesis was well supported and is thus comparatively scale-invariant. A qualitative model developed here highlighted the importance of both willow water status and disturbance in determining host plant quality, as well as an apparent trade off between shoot length and plant moisture status in determining vital rates across the altitudinal gradient. This study thus demonstrated for the first time the scale-dependent nature of mechanisms underlying the population dynamics E. lasiolepis, and identified the interaction between parasitism and altitude as a novel mechanism underlying spatial patterns in the survival and mortality patterns of this species.     

Molecular evolution of snake venom toxins

Summary Phylogenetic trees were constructed for 62 venom toxins of snakes ofProteroglyphae suborder using matrix method. The resulting tree fromMinimum Spanning Tree-Cluster Analysis technique had the lowest percent deviation (8.55). The taxonomic relationship of these toxins agrees very well with zoological opinions. However, the appearance of the tree did not directly provide a plausible evolutionary model for the toxins. A model was derived from nodal ancestral sequence calculations, comparisons between intra-and inter-generical rates of amino acid change, and generally held ideas about protein evolution. According to the model, short neurotoxin is the ancient form of snake venom toxins. The courses of evolution leading to the present intraspecific homologous toxins are explained by gene duplication and allelomorphism.     

Adrenergic receptors of isolated snake atria

Cardiac adrenergic receptors in snakes were examined using an isolated atria preparation of Naja naja and Ptyas korros. Treatments included an examination of the atrial responses to selective alpha- and beta-adrenergic agonists and antagonists. In both species, both phenylephrine and isoproterenol produced dose-dependent increases in the atrial beating rate and tension. Phenylephrine-induced increases were characterized with a high affinity and low affinity components. These positive chronotropic and inotropic effects produced by phenylephrine and isoproterenol were abolished with propranolol and in the phenylephrine-induced response phentolamine also attenuated the low affinity response and blocked the high affinity response. With catecholamines depletion via 6-OH dopamine or reserpine, the high affinity component in the phenylephrine-induced response was no longer observed. It is concluded that beta-adrenoceptors are the predominant post-synaptic adrenoceptors in snake atria. Stimulatory presynaptic alpha-adrenoceptors for modulating noradrenaline release may also be present.     

Receptor variability-driven evolution of snake toxins

Three-finger toxins(TFTs) are well-recognized nonenzymatic venom proteins found in snakes. However,although TFTs exhibit accelerated evolution, the drivers of this evolution remain poorly understood.The structural complexes between long-chainα-neurotoxins, a subfamily of TFTs, and their nicotinic acetylcholine receptor targets have been determined in previous research, providing an opportunity to address such questions. In the current study, we observed several previously identified positively selected sites(PSSs) and the highly variable C-terminal loop of these toxins at the toxin/receptor interface. Of interest, analysis of the molecular adaptation of the toxin-recognition regions in the corresponding receptors provided no statistical evidence for positive selection. However, these regions accumulated abundant amino acid variations in the receptors from the prey of snakes, suggesting that accelerated substitution of TFTs could be a consequence of adaptation to these variations. To the best of our knowledge, this atypical evolution, initially discovered in scorpions, is reported in snake toxins for the first time and may be applicable for the evolution of toxins from other venomous animals.     

The influence of food abundance,food dispersion and habitat structure on territory selection and size of an Afrotropical terrestrial insectivore

Most tropical insectivorous birds, unlike their temperate counterparts, hold and defend a feeding and breeding territory year-around. However, our understanding of ecological factors influencing territory selection and size in tropical insectivores is limited. Here we examine three prominent hypotheses relating food abundance, food dispersion (spatial arrangement of food items), and habitat structure to territoriality in the Usambara Thrush Turdus roehli. We first compared leaf-litter macro-invertebrate abundance and dispersion, and habitat structure between territories and random sites. We then examined the relation between these same ecological factors and territory size. Invertebrate abundance and dispersion were sparsely and evenly distributed across our study system and did not vary between territories and random sites. In contrast, habitat structure did vary between territories and random sites indicating the Usambara Thrush selects territories with open understorey and closed overstorey habitat. Invertebrate abundance and dispersion within territories of the Usambara Thrush were not associated with habitat structure. We believe the most likely explanation for the Usambara Thrush’s preference for open understorey and closed overstorey habitat relates to foraging behavior. Using information-theoretic model selection we found that invertebrate abundance was the highest-ranked predictor of territory size and was inversely related, consistent with food value theory of territoriality.