The first Pleistocene fossil records of Urtica kioviensis Rogow. (Urticaceae) and Potamogeton sukaczevii Wieliczk. (Potamogetonaceae) in the British Isles

Vegetation History and Archaeobotany - Seeds of the extant Urtica kioviensis Rogow. (Urticaceae) and endocarps of the extinct Potamogeton sukaczevii Wieliczk. (Potamogetonaceae) were recorded in...     

鹅掌楸属种间杂种与亲本花粉壁的超微结构的比较观察

以杂种鹅掌楸及其亲本中国鹅掌楸(Liriodendron chinense)和北美鹅掌楸(L.tulipifera)为材料,研究花粉形状及花粉壁的超微结构.结果表明,杂种与亲本间花粉壁超微结构具有明显的差异,它们可作为种间及杂种与亲本的识别与区分的依据.从杂种鹅掌楸与双亲的花粉壁的纹饰的遗传关系来看,前者花粉壁表面皱疣状隆起的纹饰表明,北美鹅掌楸花粉壁纹饰特征在杂种鹅掌楸中得到充分表现.     

The influence of hybridization on epidermal properties of birch species and the consequences for palaeoclimatic interpretations

The Fennoscandian birch population primarily consists of Betula nana, B. pendula and B. pubescens ssp. czerepanovii, the Mountain birch. Frequent hybridization between the Mountain birch and B. nana generates a wide range of genotypic and phenotypic plasticity in the subarctic birch zone of Fennoscandia. Phases of subarctic conditions prevailed during the Late Glacial in large parts of NW Europe, and palynological as well as macrofossil analysis provide some evidence for the occurrence of birch hybrids during these intervals. Leaves from genetically controlled specimens of Betula pendula, B. pubescens ssp. czerepanovii, B. nana and the hybrids B. pubescens ssp. czerepanovii × nana and B. nana × pubescens ssp. czerepanovii are investigated for their specific characteristics of the epidermis morphology. Frequency and size of epidermal cells and stomata reveal a close affinity of both hybrids to B. nana and allow a differentiation of the intermediate forms between B. nana and the Mountain birch. With respect to palaeoatmospheric CO₂ reconstructions based on stomatal index, epidermal analysis shows that a possible occurrence of hybrids in fossil leaf assemblages has no profound consequences for combined species records. However, the significant differences observed in B. nana demand the separation of this species. A comparison of the cuticle properties of B. pendula and B. pubescens from Finnish Lapland and leaf material from The Netherlands reveals a divergence of the stomatal index that may be due to differences in day light length.     

Continental molluscs of the fossil site Sandelzhausen (Miocene; Upper Freshwater Molasse from Bavaria) and their value for palaeoecological assessment

The continental mollusc fauna of Sandelzhausen (Southern Germany, Early/Middle Miocene, MN5) is presented and shown to consist of 66 snail and 3 bivalve taxa. Previous ecological interpretations were partly based on poorly preserved material and are shown to be erroneous. Within a series of quantitative samples, ecologically four mollusc communities can be distinguished (two each for terrestrial and freshwater molluscs), highly indicative of ecological conditions and changes in the landscape surrounding the fossil site as well as the locality itself. Open scrub-lands with temporary waters, as indicated by forms such as Granaria and the dominance of lymnaeids, are steadily replaced with damp forests with abundant litter and rotting wood surrounding a perennial lake with small tributaries. These more favorable conditions are indicated by an overall increase of mollusc diversity, rising abundance of planorbids, and presence of restricted forms such as Drepanotrema (intolerant to droughts) as well as certain forest dwellers such as Gastrocopta and hygromiids. Molluscs are highly sensitive to environmental changes, which is reflected in the fossil record of Sandelzhausen.      

Identification of cultivated Pandanus and Colocasia in pollen records and the implications for the study of early agriculture in New Guinea

Pollen records from the island of New Guinea, spanning the last 60 000 years, show a vegetation system sensitive to global climate change and strongly influenced by anthropogenic activity. The evidence for anthropogenic activity in pollen diagrams has focused on indirect indicators such as forest clearance, burning and increases in arable weeds. Tracing individual cultivars has proven to be very difficult as the major cultivated plants, in this case dominated by root crops, have low pollen production, are insect-pollinated or are harvested before flowering occurs. The identification of some cultivars is further restricted by limited information on pollen morphology. The pollen morphology of selected species from two genera (Pandanus and Colocasia), known to include important cultivated species, have been studied. Five pollen taxa are recognised after examination by light microscopy and scanning electron microscopy. It is shown that these can be easily distinguished on the broad criteria of pollen class, grain size and size of echini. The taxonomic and dispersal characteristics of the pollen morphology of these taxa are discussed and the implications of improved identification of cultivated species in late Quaternary pollen records are considered.     

Insight into the phylogeny of African Clariidae (Teleostei, Siluriformes): implications for their body shape evolution, biogeography, and taxonomy

The phylogenetic relationships among Clariidae species (Teleostei, Siluriformes) were assessed using 563 nucleotides of the cytochrome b mitochondrial gene. We included 32 Clariidae species representative of seven genera in our analysis. Hetropneustes fossilis (Heteropneustidae) and Clarotes laticeps (Claroteidae) were used as outgroups. The molecular data identified two evolutionary lineages that correspond on one hand to African species and on the other hand to Asian species. Morphological and osteological evolution in Clariidae did not follow an orthogenetic series. Species with robust body, strong ossified head, and large adipose fin were not ancestral ones and eel-like species were not phylogenetically related and represent independent adaptation to life in mud. Adaptation to life in deep water occurred two times independently in lake Tanganyika (with Dinotopterus cunningtoni) and in Lake Malawi (with Bathyclarias species). Molecular dating using a molecular clock of 1% divergence per million years and a comparison with fossils records allowed an estimate of the timing of cladogenesis within the species studied. The Clariidae family originated in Asia 50 MY ago but contemporary African and Asian studied species originated from a common ancestor that was present on the Arabian plate about 15 MY ago. Systematic implications of these results are also discussed.     

The chironomid fauna of four shallow,humic lakes and their representation by subfossil assemblages in the surficial sediments

A comparison of the present chironomid fauna of four shallow, humic lakes with the subfossils of surficial sediments is made. The chemistry and benthos of the lakes investigated varied greatly. Results indicate a reasonable correlation between biocenoses and thanatocenoses, but a marked under-representation ofProcladius is apparent. It is suggested that, at least in shallow, humic lakes,Procladius be excluded in attempts to reconstruct chironomid communities from subfossils.     

Approximations and their consequences for dynamic modelling of signal transduction pathways

Signal transduction is the process by which the cell converts one kind of signal or stimulus into another. This involves a sequence of biochemical reactions, carried out by proteins. The dynamic response of complex cell signalling networks can be modelled and simulated in the framework of chemical kinetics. The mathematical formulation of chemical kinetics results in a system of coupled differential equations. Simplifications can arise through assumptions and approximations. The paper provides a critical discussion of frequently employed approximations in dynamic modelling of signal transduction pathways. We discuss the requirements for conservation laws, steady state approximations, and the neglect of components. We show how these approximations simplify the mathematical treatment of biochemical networks but we also demonstrate differences between the complete system and its approximations with respect to the transient and steady state behavior.     

The first record for Melittobia australica Girault in New Zealand and new host records for Melittobia (Eulophidae)

Abstract

Melittobia australica Girault is a new record for New Zealand and from Vespula spp. In the Wellington district, M. australica was found in an embryo colony of the German wasp Vespula germanica (Fabricius) and in pupae of the mason wasp Pison spinolae Shuckard in 1980 and 1981 respectively. Melittobia was recorded in nests of P. morosum Smith in Canterbury, New Zealand in 1976 and 1977. The original sources of M. australica were considered.

The validity of the earliest record of Melittobia in a social wasp host is reconsidered. It is concluded Melittobia has been underated as a parasite of social wasps.     

The presence of heterospecific pollen on stigmas of nectariferous and nectarless orchids and its consequences for their reproductive success

Summary The widespread occurrence of nonorchid, heterospecific pollen grains on the stigmatic surfaces of a range of nectariferous and nectarless European orchids (Dactylorhiza. Orchis, Goodyera, andGymnadenia species) is reported for the first time, and the impact of heterospecific pollination on orchid reproductive success is experimentally investigated. There are three main components of stigmatic contamination by heterospecific pollen: the frequency of contamination, the diversity of foreign species present on the stigma, and the amount of pollen deposited. Six out of seven of the species examined have greater than 85% of stigmas contaminated with wind and insect-dispersed pollen. From one to nine insect-dispersed foreign pollen species are present per stigma, including pollen of members of the families Apiaceae, Asteraceae, Caryohpyllaceae, Ericaceae, and Primulaceae. Average loads per stigma vary from 13 to 176 grains, with individual stigma loads ranging from one to 909. Whether or not the orchid provides nectar has a major impact on these three components. Nectarless orchids have the greatest frequencies of contamination, diversity of species, and average load per stigma. Insect-dispersed pollen is deposited both by pollinators and visitors but, in spite of low levels of pollination, nectarless orchids still exhibit higher frequencies of heterospecific pollen contamination. The effect of the presence of heterospecific pollen on the reproductive success of orchids is tested in this study for the first time. Average-to-high, naturally occurring loads of heterospecific pollen derived from a mixture ofArmeria maritima,Caltha palustris,Cochlearia officinalis,Cytisus scoparius, andPrimula vulgaris and consisting of 50–250 grains per load are placed onto stigmas ofDactylorhiza purpurella which are subsequently self-pollinated with half of a pollinium. All pollinations produce capsules indicating that heterospecific pollen does not affect fruit set. Although experimental and control fruits are similar in size, they differ in total seed weight and composition. Total seed weight is reduced and the proportion of seeds with normal embryos decreased while the proportion of unfertilised ovules increased following pollination with heterospecific pollen, indicating a detrimental effect on fertilisation. Lower reproductive success caused by fertilisation failure is likely to be most severe in nectarless species because of their generally higher levels of contaminated stigmas. As nectarless orchids are known to have lower fruit set compared with nectariferous ones, this finding suggests that the reproductive success of nectarless orchids may be even lower than previously realised.Abbreviations RS reproductive success     

Botanical macro-remains and insects from the Eemian and Weichselian site of Oerel (northwest Germany) and their evidence for the history of climate

The late Pleistocene site of Oerel which represents the Eemian and the Weichselian interstadials Brörup, Odderade, Oerel and Glinde as well as parts of the stadials Herning and Rederstall was investigated for botanical remains such as fruits, seeds, wood, leaves and mosses, as well as insect remains. A large number of taxa were identified. They show the different environmental conditions, in particular several changes of water level leading to the formation of lakes and diverse forms of mires up to raised bogs. The trophic conditions, too, changed several times. The macrofossil record supports the pollen evidence of dense forests during the two early Weichselian interstadials and tundra vegetation during the later ones. Several indicator species show comparably warm summers but very cold winters during the Brörup and Odderade while the climate during Oerel and Glinde was generally cool. Climatic reconstructions using the MCR method were performed on the basis of the beetle finds.     

Physicians' beliefs and behaviour during a randomized controlled trial of episiotomy: consequences for women in their care.

OBJECTIVE: To evaluate whether physicians'' beliefs concerning episiotomy are related to their use of procedures and to differential outcomes in childbirth. DESIGN: Post-hoc cohort analysis of physicians and patients involved in a randomized controlled trial of episiotomy. SETTING: Two tertiary care hospitals and one community hospital in Montreal. PARTICIPANTS: Of the 703 women at low risk of medical or obstetric problems enrolled in the trial we studied 447 women (226 primiparous and 221 multiparous) attended by 43 physicians. Subjects attended by residents or nurses were excluded. MAIN OUTCOME MEASURES: Patients: intact perineum v. perineal trauma, length of labour, procedures used (instrumental delivery, oxytocin augmentation of labour, cesarean section and episiotomy), position for birth, rate of and reasons for not assigning women to a study arm, postpartum perineal pain and satisfaction with the birth experience, physicians: beliefs concerning episiotomy. RESULTS: Women attended by physicians who viewed episiotomy very unfavorably were more likely than women attended by the other physicians to have an intact perineum (23% v. 11% to 13%, p < 0.05) and to experience less perineal trauma. The first stage of labour was 2.3 to 3.5 hours shorter for women attended by physicians who viewed episiotomy favourably than for women attended by physicians who viewed episiotomy very unfavorably (p < 0.05 to < 0.01), and the former physicians were more likely to use oxytocin augmentation of labour. Physicians who viewed episiotomy more favourably failed more often than those who viewed the procedure very unfavourably to assign patients to a study arm late in labour (odds ratio [OR] 1.88, p < 0.05), both overall and because they felt that "fetal distress" or cesarean section necessitated exclusion of the subject. They used the lithotomy position for birth more often (OR 3.94 to 4.55, p < 0.001), had difficulty limiting episiotomy in the restricted-use arm of the trial and diagnosed fetal distress and perineal inadequacy more often than the comparison groups. The patients of physicians who viewed episiotomy very favourably experienced more perineal pain (p < 0.01), and of those who viewed episiotomy favourably and very favourably experienced less satisfaction with the birth experience (p < 0.01) than the patients of physicians who viewed the procedure very unfavourably. CONCLUSIONS: Physicians with favourably views of episiotomy were more likely to use techniques to expedite labour, and their patients were more likely to have perineal trauma and to be less satisfied with the birth experience. This evidence that physician beliefs can influence patient outcomes has both clinical and research implications.     

Prions and protein inhibitors of proteinases: structural analogies and their consequences. IV. The nature of the interspecies barrier of prion disease

Declining of unproved supposition about the transformation of the cellular isoform of prion protein into pathogenic one allows the pathogenesis of prion diseases to be reduced to the series of interdependent processes caused by prion-mediated selective damage of the components of the cell chaperoning system with following membrane folding of the de novo synthesized prion protein. Dependence of the level of the cell chaperoning system damage on the similarity of the sequences of cellular and infectious prion proteins explains exhaustively the existence of interspecies barrier in prion pathogenesis as well as makes it natural and inevitable property of the latter. The structural ensurance of separate prion diseases strains, their transformation at repeated infectious passages commonly with known and supposed ways for prion-less initiation of spongiform encephalopathies are discussed.     

Growth and energetics of Leuconostoc mesenteroides NRRL B-1299 during metabolism of various sugars and their consequences for dextransucrase production.

The metabolic and energetic properties of Leuconostoc mesenteroides have been examined with the goal of better understanding the parameters which affect dextransucrase activity and hence allowing the development of strategies for improved dextransucrase production. Glucose and fructose support equivalent specific growth rates (0.6 h-1) under aerobic conditions, but glucose leads to a better biomass yield in anaerobiosis. Both sugars are phosphorylated by specific hexokinases and catabolized through the heterofermentative phosphoketolase pathway. During sucrose-grown cultures, a large fraction of sucrose is converted outside the cell by dextransucrase into dextran and fructose and does not support growth. The other fraction enters the cell, where it is phosphorylated by an inducible sucrose phosphorylase and converted to glucose-6-phosphate (G-6-P) by a constitutive phosphoglucomutase and to heterofermentative products (lactate, acetate, and ethanol). Sucrose supports a higher growth rate (0.98 h-1) than the monosaccharides. When fructose is not consumed simultaneously with G-1-P, the biomass yield relative to ATP is high (16.8 mol of ATP.mol of sucrose-1), and dextransucrase production is directly proportional to growth. However, when the fructose moiety is used, a sink of energy is observed, and dextransucrase production is no longer correlated with growth. As a consequence, fructose catabolism must be avoided to improve the amount of dextransucrase synthesized.     

Pollen morphology of Chinese Curcuma L. and Boesenbergia Kuntz (Zingiberaceae): Taxonomic implications

In order to find new non-molecular evidence to support the phylogenetic and taxonomic position, pollen grains of 20 populations of 16 species of Chinese Curcuma L. and Boesenbergia Kuntz (Zingiberaceae) were investigated under SEM and TEM. The pollen grains are spherical and ovoid, nonaperturate. The pollen wall is composed of a very thin exine and a thick intine. The exine is psilate or echinate. The intine consists of two layers, i.e., a thick, channeled layer (exintine) and an inner homogenous layer (endintine). The results reveal morphological congruence between the pollen grains of species of Curcuma, which according to DNA sequence data appears to be a polyphyletic genus. However the uniform pollen morphology in Curcuma provides no evidence to divide this genus into separate taxonomic entities. Our results on pollen morphology also do not provide any additional evidence to either unite or segregate Boesenbergia albomaculata and Curcumorpha longiflora in the same genus and demonstrate that more taxonomic data on the genus Boesenbergia and its relatives are needed before a final decision can be made.     

The association between pollen size and Renner complex in Oenothera villaricae and O. picensis ssp. picensis and their hybrids: evidence for preanthesis pollen competition

In both Oenothera villaricae Dietrich and O. picensis ssp. picensis, chromosomes are transmitted as two Renner complexes. Reciprocal combinations of the Renner complexes produce eight different F₁ hybrids, but only seven are viable. Each species, and each F₁ hybrid, produces three sizes of pollen, approximately 50% small sterile grains, 15% medium-sized viable grains and 35% large viable grains. Medium- and large-sized grains were separated manually and subjected to random amplified polymorphic DNAs (RAPDs) analysis. A pattern of RAPD amplifications was obtained which indicates that, for each species and F₁ hybrid, one specific Renner complex characterizes the medium- and another the large-sized viable pollen. The results indicate that pollen size is determined in part by the pollen genotype and in part by the genotype of the other pollen grains developing within the same anther.