Biomineralization of limpet teeth: a cryo-TEM study of the organic matrix and the onset of mineral deposition

The continuously growing limpet radula contains teeth at various stages of maturity and thus provides an excellent opportunity for studying the processes and mechanisms of their mineralization. We report here on our structural investigations of the pre-formed chitin matrix and the initial deposition and growth of goethite (α-FeOOH) crystals within the matrix. By using cryo-techniques, in which unstained sections of the teeth are examined in a frozen-hydrated state in a transmission electron microscope (TEM), we were able to characterize the process without introducing artifacts normally associated with the staining, dehydration, and embedding required for conventional TEM. The unmineralized matrix consists of relatively well ordered, densely packed arrays of chitin fibers, with only a few nanometers between adjacent fibers. There are clearly no pre-formed compartments that control goethite crystal size and shape; rather, crystals must push aside or engulf the fibers as they grow. By examining teeth nearly row-by-row around the onset of mineralization, we were able to image the first-formed mineral within the chitin matrix. These linear deposits of goethite appear to nucleate on the chitin fibers, which thus control the orientation of the crystals. Crystal growth, on the other hand, is apparently not influenced by the matrix, in contrast to many other biomineralization systems.     

Molecular,phytochemical and morphological characterization of the liverwort genus Radula in Portugal (mainland,Madeira, Azores)

Relationships of the eight species of the liverwort genus Radula occurring in Portugal (mainland, the Madeira and Azores archipelagos), including the Macaronesian endemics R. jonesii and R. wichurae, were evaluated based on molecular, phytochemical and morphological–anatomical data. Maximum parsimony and Bayesian analyses were performed with sequences from three plastid DNA markers (trnS _GGA-rps4 spacer, rps4 gene, trnL _UAA intron), volatile oil compounds, as well as qualitative morphological–anatomical characters. In addition, the molecular data were subjected to maximum likelihood analysis. The eight taxa, R. aquilegia, R. carringtonii, R. complanata, R. holtii, R. jonesii, R. lindenbergiana, R. nudicaulis and R. wichurae, can be clearly distinguished from each other, either by molecular data alone or by combination of characters from all three data sets. Radula aquilegia is monophyletic according to the molecular data, but shows considerable, yet undescribed intraspecific morphological and phytochemical variability. Recognition of R. complanata and R. lindenbergiana as separate species, previously based solely on the paroecious vs. dioecious sexual condition, is moderately supported by the molecular phylogenetic analyses and strongly supported by the phytochemical data. The Radula species, narrowly distributed in Macaronesia and Atlantic Europe, probably have two different origins. For Radula holtii and R. nudicaulis, connections with Radula species from the Neotropics are indicated. The other species, among them the two Macaronesian endemics, are closely related with the R. complanata/R. lindenbergiana complex, which is widely distributed in the northern hemisphere.     

Field experiments with “cageless” methods to manipulate grazing gastropods on intertidal rocky shores

Excluding particular species or guilds of grazing gastropods from experimental areas on intertidal rocky shores is a manipulation frequently used by marine ecologists. Manual removals, cages or fences are classical methods, but they usually require large areas or multiple procedural controls to avoid experimental artefacts. In order to minimise some of those constraints, alternative methods have been developed and are increasingly being used. The effects and limitations of these methods are, however, generally assumed and hardly ever tested. The experiment described here was designed to compare the effectiveness of manual removals, copper paint and sticky barriers in excluding intertidal grazing gastropods from experimental areas on a natural sandstone platform in South-eastern Australia. The response of the grazing assemblage was evaluated for individual species and collectively (integrating all species) by direct counts of individuals and from radular marks on wax discs. The observed patterns varied considerably among species. As predicted, barriers of copper paint effectively excluded the limpet Cellana tramoserica, for several weeks, while having no apparent effect on co-occurring species of grazing gastropods. Sticky barriers were also effective in excluding C. tramoserica, but for shorter periods of time. Contrary to expectations, however, sticky barriers were generally incapable of deterring the coiled snails Bembicium nanum and Nerita atramentosa. Barriers of copper paint are, therefore, a cost-effective way to manipulate diversity (densities of individuals, number and composition of species) and function (intensity of grazing) in this type of assemblage. Care must be taken to clarify the underlying mechanisms and to identify adequate procedural controls.     

伞形琥珀螺（腹足纲，琥珀螺科）的形态解剖结构

伞形琥珀螺(Succinea daucina),最早由Pfeiffer在1854年报道。本文采用形态解剖学的方法对采自新疆乌鲁木齐南山西白杨沟(43°24.674′N,87°08.620′E,海拔1 785 m)的伞形琥珀螺进行了观察。测量并解剖了贝壳颜色分别为黄棕色和浅黄色的性成熟个体各10只,绘制了内部解剖图,应用电子扫描显微镜对两种壳色各3只个体齿舌、颚片的显微结构进行了观察和拍摄记录。伞形琥珀螺贝壳为长卵圆形,中等大小,壳高10.06~12.90 mm,壳宽6.28~8.56 mm,壳质薄,有3~3.5个螺层。其齿式为16-21:10-13:1:10-13:16-21,中央齿三锥型,侧齿和边缘齿双锥型。软体乳白色,色素点少。储精囊一个,蛋白腺、前列腺大,阴茎管状,约3/4被阴茎鞘包裹。两种壳色标本的齿舌、颚片及内部解剖特征相同,为同一种,即伞形琥珀螺。     

四种翁戎螺的齿舌形态及功能

翁戎螺（Pleurotomariidae）起源于寒武纪时期,是介于软体动物祖先和现代腹足类之间的过渡类型。目前我国翁戎螺的分类、生态等方面研究不足,为探究翁戎螺的形态分类及食性,以寺町翁戎螺（Bayerotrochus teramachii）、红翁戎螺（Mikadotrochus hirasei）、高腰翁戎螺（M. salmianus）和龙宫翁戎螺（Entemnotrochus rumphii）为研究对象,应用扫描电镜观察其齿舌结构。结果表明,（1）翁戎螺齿舌结构与大多数腹足类具有3种类型的齿舌不同,其齿舌带上具有中央齿、内侧齿、外侧齿、镰状齿、丝状齿和桨状齿6种不同类型的小齿。（2）4种翁戎螺的中央齿均为1枚,内侧齿2或3枚,外侧齿20 ~ 25枚,镰状齿16 ~ 32枚,丝状齿35 ~ 62枚,桨状齿10 ~ 26枚。（3）翁戎螺属（Mikadotrochus）内种类之间齿舌形态的差异较小,进行种间区分需结合其小齿数量,但属间差异较大,中央齿、内侧齿、镰状齿的齿尖和齿基形态都可以进行属间区分。（4）龙宫翁戎螺齿舌带每个横排具有26枚桨状齿,与之前研究具有10枚不同。本研究对翁戎螺镰状齿和丝状齿之间、丝状齿和桨状齿之间的过渡形态进行深入地描述和划分。本研究结果可为我国翁戎螺的形态分类研究提供资料。     

Characterization of the Contents of Oil Bodies from the Liverwort Radula complanata1

Abstract: With a combination of enzymatic treatment and micromanipulation, the contents of oil bodies of Radula complanata were obtained. A GC‐MS analysis revealed that 3‐methoxybibenzyl is the main constituent of these compartments. Its structure was elucidated by NMR spectroscopy.     

Experimental habitat fragmentation increases linkage disequilibrium but does not affect genetic diversity or population structure in the Amazonian liverwort Radula flaccida

Habitat fragmentation increases the migration distances among remnant populations, and is predicted to play a significant role in altering both demographic and genetic processes. Nevertheless, few studies have evaluated the genetic consequences of habitat fragmentation in light of information about population dynamics in the same set of organisms. In a 10,000-km(2) experimentally fragmented landscape of rainforest reserves in central Amazonia, we examine patterns of genetic variation (amplified fragment length polymorphisms, AFLPs) in the epiphyllous (e.g. leaf-inhabiting) liverwort Radula flaccida Gott. Previous demographic work indicates that colonization rates in this species are significantly reduced in small forest reserves. We scored 113 polymorphic loci in 86 individuals representing five fragmented and five experimentally unmanipulated populations. Most of the variation (82%) in all populations was harboured at the smallest (400 m(2)) sampling unit. The mean ((+/-) SD) within-population genetic diversity (Nei's), of forest remnants (0.412 +/- 0.2) was indistinguishable from continuous (0.413 +/- 0.2) forests. Similarly, F(ST) was identical among small (1- and 10-ha) and large (> or = 100-ha) reserves (0.19 and 0.18, respectively), but linkage disequilibrium between pairs of loci was significantly elevated in fragmented populations relative to those in continuous forests. These results illustrate that inferences regarding the long-term viability of fragmented populations based on neutral marker data alone must be viewed with caution, and underscore the importance of jointly evaluating information on both genetic structure and demography. Second, multilocus analyses may be more sensitive to the effects of fragmentation in the short term, although the effects of increasing linkage disequilibrium on population viability remain uncertain.     

Composition of the essential oil of the liverwort Radula perrottetii of Japanese origin

Analysis of the essential oil of the liverwort Radula perrottetii afforded two novel viscidane diterpenes, viscida-3,9,14-triene (1), viscida-3,11(18),14-triene (2), four bisabolane sesquiterpenes, bisabola-2,6,11-triene (3), bisabola-1,3,5,7(14),11-pentaene (4), bisabola-1,3,5,7,11-pentaene (5), 6,7-epoxybisabola-2,11-diene (6), and 1-methoxy-4-(2-methylpropenyl)benzene (7) as new natural products. In addition, the known compounds bisabola-1,3,5,7(14),10-pentaene (8), ar-tenuifolene (9), alpha-helmiscapene (10), and beta-helmiscapene (11) were also isolated. Isolation was carried out by preparative gas chromatography, and the structures were established by extensive NMR analysis. This is the first finding of viscidane diterpenes in liverworts. Compounds 8, 9 and the rarely encountered eudesmane sesquiterpene hydrocarbons 10 and 11 are reported for the first time from R. perrottetii.     

海洋软体动物齿舌中磁铁物的研究

在扫描电镜下对红条毛肤石鳖（ Ａｃａｎｔｈｏｃｈｉｔｏｎ ｒｕｂｒｏｌｉｎｅａｔｕｓ Ｌｉｓｃｈｋｅ） 齿舌进行了观察,用原子力和磁力显微镜及超导量子干涉器（ＳＱＵＩＤ） 式磁强计对齿舌中的磁铁物Ｆｅ３ Ｏ４ 进行了分析和测量,实验证明齿舌中含有磁铁物Ｆｅ３ Ｏ４ ,每个齿舌约含Ｆｅ３ Ｏ４ ０．２ ｍｇ ,占齿舌重量的１５ ％ ,矿物重量的４０％ ,磁化强度约为０．０２×１０ － ３ Ａｍ２／ 个,相当于１４Ａｍ２／ｋｇ ,并且磁铁物主要存在于第一侧齿的齿尖上,同时Ｆｅ３ Ｏ４ 晶体在齿片表面上的排列及磁畴结构具有方向性。     

A ‘conovenomic’ analysis of the milked venom from the mollusk-hunting cone snail Conus textile—The pharmacological importance of post-translational modifications

Cone snail venoms provide a largely untapped source of novel peptide drug leads. To enhance the discovery phase, a detailed comparative proteomic analysis was undertaken on milked venom from the mollusk-hunting cone snail, Conus textile, from three different geographic locations (Hawai’i, American Samoa and Australia's Great Barrier Reef). A novel milked venom conopeptide rich in post-translational modifications was discovered, characterized and named α-conotoxin TxIC. We assign this conopeptide to the 4/7 α-conotoxin family based on the peptide's sequence homology and cDNA pre-propeptide alignment. Pharmacologically, α-conotoxin TxIC demonstrates minimal activity on human acetylcholine receptor models (100 μM, <5% inhibition), compared to its high paralytic potency in invertebrates, PD₅₀ = 34.2 nMol kg⁻¹. The non-post-translationally modified form, [Pro]^2,8[Glu]¹⁶α-conotoxin TxIC, demonstrates differential selectivity for the α3β2 isoform of the nicotinic acetylcholine receptor with maximal inhibition of 96% and an observed IC₅₀ of 5.4 ± 0.5 μM. Interestingly its comparative PD₅₀ (3.6 μMol kg⁻¹) in invertebrates was ∼100 fold more than that of the native peptide. Differentiating α-conotoxin TxIC from other α-conotoxins is the high degree of post-translational modification (44% of residues). This includes the incorporation of γ-carboxyglutamic acid, two moieties of 4-trans hydroxyproline, two disulfide bond linkages, and C-terminal amidation. These findings expand upon the known chemical diversity of α-conotoxins and illustrate a potential driver of toxin phyla-selectivity within Conus.