首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 31 毫秒
1.
Research on the influence of sea level variations on the benthic faunas have been carried out in the Upper Ordovician of Sardinia. Study of the depositional facies and sequence analysis of the upper part (Lower Ashgill) of the Portixeddu Formation led to the identification of the sedimentary environments. Cystoids and crinoids are associated to bryozoans and brachiopods in most levels. The numerical analysis of associations and megaguilds shows that crinoids and cystoids have a higher frequency in the proximal and median facies of the upper offshore. The columnal association characterized by Conspectocrinus celticus and the coronoid Mespilocystites tregarvanicus has been discovered in the upper part of the formation. This material and complementary samples from Upper Ordovician of Sardinia and Kabylia (Algeria) bring additional data on the systematic and show the wide distribution of this fauna outside of the Ibero-armorican domain. The distribution of this echinoderm association supports a palaeogeographical position of the Ibero-armorican domain and Sardinia within the north gondwanan margin during the Lower Palaeozoic.  相似文献   

2.
The pollen analysis of sediments of two boreholes located in the northeastern Morocco (Nador 1) and in the southeastern Spain (Andalucia G1) has allowed shedding a new light on the vegetation and climate of the North African littoral plains, the Rif Massif and the Betic Range during the Pliocene. The vegetation around the Alboran Sea was open and xeric during the Zanclean, dominated by herbs including subdesertic elements as Calligonum, Lygeum, Nitraria and Neurada. This type of vegetation indicates a dry and hot climate. The southwestern Mediterranean steppes have therefore a climatic character; they existed before the presence and the heavy pressure of Man on the environment. From the Piacenzian, the development, at Andalucia as well as at Nador, of Artemisia and the appearance of some altitude trees such as Cedrus and Cathaya indicate a vegetation change linked to a climatic change. Modifications in the vegetation observed during the same period in northwestern Mediterranean seem to indicate that the vegetation changes observed at Andalucia and Nador are controlled by the appearance of the first arctic glacial-interglacial cycles. The cedar tree appears at Nador only at the end of the Piacenzian, at time of the first cooling, while it has been found punctually in Messinian and early Pliocene sediments of Habibas in Algeria and in Messinian sediments of the Bou Regreg section at Salé in Morocco. The regular presence of Cedar at Bou Regreg during the Messinian, allows supposing that it was present in the Middle Atlas Mountains and that its development was favoured by colder conditions.  相似文献   

3.
This paper explores the cultural sequence for the period 12,500–9000 BP in the Mediterranean coast of the Iberian Peninsula. According to the traditional division by Fortea, this period starts with the end of the Upper Magdalenian, followed by two facies: the Microlaminar Epipalaeolithic and the Geometric Epipalaeolithic (Filador type), (related to Sauveterrian facies). The data collected in recent years suggest a change or amendment to this previous proposal, which now would be divided into four phases: Final Upper Magdalenian, Early Epimagdalenian, Recent Epimagdalenian and Microlaminar Sauveterroid. This paper discusses each of these periods examining the evolution of the stone tools and concluding that in the Mediterranean coast of the Iberian Peninsula the Magdalenian tradition continues with little changes until the advent of the Mesolithic.  相似文献   

4.
The origin of the Upper Palaeolithic around the Mediterranean was the result of the local evolution, particularly in the Near East and in the Lower Nile basin, and of the migration from this zone to South-Eastern and Central Europe. The Initial Upper Palaeolithic in the Near East belt was the effect of local evolution from the industries based on Levallois concept to the industries which developed leptolithic blade technologies. This evolution is well registered in multi-layer sites in the Syro-Palestinian belt (Emirian/Ahmarian), which was the starting point of the diffusion of these “transitional” industries in South-Eastern and Central Europe. This diffusion could be identified with the migration of first anatomically Modern Humans. The Early Upper Palaeolithic in Europe — dated to the second half of the Interpleniglacial — was, at least partially, based on these “transitional” industries and manifested by the appearance of the Aurignacian, contrasted with local cultures such as the Uluzzian in Mediterranean Europe. During whole the Interpleniglacial Europe was separated from Northern Africa dominated by local evolution of Middle Palaeolithic (Middle Stone Age) cultures (mostly expressed by the Aterian), and by specific “transitional” industries on the southern Mediterranean coast (Early Dabbian) and in the Lower Nile basin. The Last Glacial Maximum and the corresponding sea level recession opened new possibilities of contacts between the Maghreb and the Iberian Peninsula in both directions (Aterian-Solutrean and Gravettian-Early Iberomaurusian), which are still difficult to be proved before new chronostratigraphic correlations are made. At the same time we register links between south-eastern Europe and western Anatolia; the real border between Near Eastern and European Mediterranean cultural zones was marked, in the Late Glacial, by the Taurus chain. During the Late Glacial the cultural separation between Europe and Africa was particularly marked. Only in the Aegean basin the first sea navigation facilitated contacts which become widespread as late as in the Early Holocene with neolithization trough maritime contacts.  相似文献   

5.
A phylogenetic analysis of 123 morphological characters of basal waterfowl (Aves: Anseriformes) and other selected avian orders confirmed that the screamers (Anhimae: Anhitn-idae) are the sister-group of other waterfowl (Anseres), and that the magpie goose (Anseranatidae: Anseranas semipalmata) is the sister group of other modern waterfowl exclusive of screamers (Anatidae sensu stricto). The analysis also supports the traditional hypothesis of the gallinaceous birds (Galliformes) as the sister group of the Anseriformes. Presbyornis, a fossil from the early Eocene of Wyoming and averred by Olson & Feduccia as showing that the Anseriformes were derived from shorebirds (Charadriiformes), was found to represent the sister group of the Anatidae. Associated hypotheses by Olson & Feduccia concerning the implications of Presbyornis for the phylogenetic relationships of flamingos (Phoenicopteriformes), the position of the Anhimidae within the waterfowl, relationships among modern Anatidae, and a plausible evolutionary scenario for waterfowl also are rejected. Analyses revealed that cranial characters were critical to the establishment of the Galliformes as the sister group of the Anseriformes; exclusion of the Anhimidae, especially in combination with Anseranas, also undermined the support for this inference. Placement of Presbyornis as the sister group of the Anatidae casts doubt on the role suggested by Feduccia of ‘transitional shorebirds' in the origin of modern avian orders, and calls into question the concept of ‘fossil mosaics’. The phylogenetic hypothesis is used to reconstruct an evolutionary scenario for selected ecomorphological characters in the galliform-anseriform transition, to predict the most parsimonious states of these characters for Presbyornis, and to propose a phylogenetic classification of the higher-order taxa of waterfowl. This re-examination of Presbyornis also is used to exemplify the fundamental methodological shortcomings of the intuitive approach to the reconstruction of phylogenetic relationships.  相似文献   

6.
Foliar sclereids in the Magnoliaceae   总被引:4,自引:0,他引:4  
The foliar sclereids in 136 species representing 11 of the 12 genera of Magnoliaceae were studied and compared. Sclereids occur in four different cell assemblages within the leaf: diffuse idioblasts, mesophyll, dermal system, and the vein sheath including terminal elements. Tropical members tend to have the most highly sclerified leaves. In species of Manglietia the leaves have sclerified spongy mesophyll and either sclerified epidermis or hypodermis. In Talauma , sclerification affects the vein sheath and terminal cells of veinlets, with a specialized thick marginal vein in the Asian taxa but not in the American ones. Liriodendron and the magnolias native to the north temperate zone have only minimal sclerification, which usually is confined to the vein sheath of the midrib and the main lateral veins, and as idioblastic sclereids in the petiole and the midrib near the base of the blade. The two largest genera Magnolia and Michelia are heterogeneous and include species which vary as to their combinations of sclerified elements among the four possible types.  相似文献   

7.
Zhang  Qingmeng  Ahmed  Niaz  Gao  George F.  Zhang  Fengmin 《中国病毒学》2020,35(6):868-874
In this article, we systematically review Dr. Wu Lien-Teh's academic achievements and outstanding contributions in the prevention and control of the plague epidemic in northeast China and introduce the development of the earliest public health epidemic prevention system in China in order to commemorate the 140th anniversary of Dr. Wu Lien-Teh's birth. We hope that this article will provide insights into the effective prevention and control of emerging infectious diseases as well as the current worldwide pandemic of COVID-19, facilitating the improvement and development of public health systems in China and around the globe.  相似文献   

8.
Evolutionary expansion of the Monogenea   总被引:5,自引:0,他引:5  
The evolutionary expansion of the monogeneans has taken place in parallel with the diversification of the fish-like vertebrates. In this article the main trends in monogenean evolution are traced from a hypothetical skin-parasitic ancestor on early vertebrates. Special consideration is given to the following topics: early divergence between skin feeders and blood feeders; diversification and specialization of the haptor for attachment to skin; transfer from host to host, viviparity and the success of the gyrodactylids; predation on skin parasites and camouflage; colonization of the buccal and branchial cavities; diversification and specialization of the haptor for attachment to the gills; phoresy in gill parasites; the development of endoparasitism and the origin of the cestodes; the success of dactylogyroidean gill parasites; the uniqueness of the polyopisthocotyleans; ovoviviparity and the colonization of the tetrapods. Host specificity has been the guiding force of coevolution between monogeneans and their vertebrate hosts, but the establishment of monogeneans on unrelated hosts sharing the same environment (host-switching) may have been underestimated. Host-switching has provided significant opportunities for evolutionary change of direction and is probably responsible for the establishment of monogeneans on cephalopod molluscs, on the hippopotamus and possibly on chelonians. There are indications that host-switching may be more common in monogeneans that spread by direct transfer of adults/juveniles from host to host. A limitation on the further expansion of monogeneans is the need for water for the dispersal of the infective larva (oncomiracidium).  相似文献   

9.
In the newly laid egg of the mayfly Ephemera japonica, an egg nucleus (oocyte nucleus) at metaphase of the first maturation division is in the polar plasm at the mid-ventral side of the egg, and a male pronucleus lies in the periplasm beneath a micropyle situated just opposite the polar plasm or at the mid-dorsal side of egg. The maturation divisions are typical. An extensive and circuitous migration of the male pronucleus is involved in the fertilization process: it first moves anteriad in the periplasm from beneath the micropyle to the anterior pole of the egg and then turns posteriad in the yolk along the egg's long axis to the site of syngamy, near the center of the egg. Cleavage is superficial. The successive eight cleavages, of which the first five are synchronized, result in the formation of the blastoderm, and about ten primary yolk cells remain behind in the yolk. Even in the newly formed blastoderm, the thick embryonic posterior half and the thin extraembryonic anterior half areas are distinguished: the former cells are concentrated at the posterior pole of the egg to form the germ disc, and the latter cells become more flattened, forming serosa. Time-lapse VTR observations reveal a yolk stream that is in accord with the migration of the male pronucleus in time and direction. The yolk stream is also generated in activated unfertilized eggs, and it is probable that the migration of the male pronucleus in association with the fertilization may be directed by the yolk stream. J. Morphol. 238:327–335, 1998. © 1998 Wiley-Liss, Inc.  相似文献   

10.
Pollen analysis of Madonna dell’Arma cave inside part (Liguria, Italy) allowed us to reconstitute, at local scale, the Ligurian coastal vegetation between the end of the last interglacial period and the beginning of the pleniglacial. This transition period shows an important representation of arboreal cover and a persistence of thermophilous elements that allowed us to considerate the western Liguria as a periglacial refuge. During the end of the last interglacial, xerophytic, halophytic herbs and shrubs taken over from a Mediterranean pre-forest unit in the first slopes constituted the coastal zone. The nearness of Argentina torrent and the Armea influenced, in the coast, the existence of marshy zones colonized by hygrophilous trees. In the Ligurian lowlands spread out sclerophyllous and mesophilous forests according to altitude. The beginning of the pleniglacial is indicated in the sequence by increases of Pinus, Cupressaceae and Artemisia in the context of a decline in the thermophilous components. This picture of vegetation has become integrated into the multidisciplinary studies of the site and contributed to the elaboration of palaeoclimatic hypothesis similar as those revealed by the fauna.  相似文献   

11.
Retinal detachment (RD) describes a separation of the neurosensory retina from the retinal pigmented epithelium (RPE). The RPE is essential for normal function of the light sensitive neurons, the photoreceptors. Detachment of the retina from the RPE creates a physical gap that is filled with extracellular fluid. RD initiates cellular and molecular adverse events that affect both the neurosensory retina and the RPE since the physiological exchange of ions and metabolites is severely perturbed. The consequence for vision is related to the duration of the detachment since a rapid reapposition of the two tissues results in the restoration of vision 1. The treatment of RD is exclusively surgical. Removal of vitreous gel (vitrectomy) is followed by the removal non essential part of the retina around the detached area to favor retinal detachment. The removed retinal specimens are res nullius (nothing) and consequently normally discarded. To recover RNA from these surgical specimens, we developed the procedure jouRNAl that allows RNA conservation during the transfer from the surgical block to the laboratory. We also standardized a protocol to purify RNA by cesium chloride ultracentrifugation to assure that the purified RNAs are suitable for global gene expression analysis. The quality of the RNA was validated both by RT-PCR and microarray analysis. Analysis of the data shows a simultaneous involvement of inflammation and photoreceptor degeneration during RD.  相似文献   

12.
M. Yamauchi 《Plant and Soil》1989,117(2):275-286
Rice plants with bronzing, collected from fields in central and southern Nigeria, where the soils consisted of Tropaquent, Tropaquult and Tropaquept, showed higher iron and lower potassium, phosphorus, and magnesium concentrations than plants with little or no bronzing. Pot experiments with the soils indicated that the severity of the bronzing was affected not only by the iron concentration in the shoots but also by the potassium concentration. The application of chloride compounds to the soil increased severity of the bronzing and lead to deterioration of growth, whereas the application of sulfate compounds was beneficial.The application of potassium sulfate reduced the severity of bronzing and increased the dry matter production of rice plants grown in the field. The concentration and accumulation of potassium in the shoots increased when the bronzing severity decreased and the iron concentration was decreased by the dilution effect caused by the increased dry matter production.  相似文献   

13.
The Lias and Dogger series in the southern Paris Basin outcrops are precisely dated following the ammonite biozonation scale. In these series, the depositional environment context is accurately identified and thus various isopic zones can bee recognized. From the outcrop study, the depositional sequence and the tectonics events are also distinguished. The poorly dated subsurface data should be not anymore interpreted as diagraphic signatures, with the traditional peak to peak correlation. They now need to be analysed according to the geodynamic evolution of each isopic zone. The Liassic transgressive series (in the Armorican continent) and the Dogger platforms numerous carbonate bodies are correlated at biostratigraphic scale, throughout the whole southern Paris Basin. Subsequently, paleogeographic maps are established and based on depositional sequences. The basin evolution image changes radically. This shows clearly that the complexes carbonate bodies layout prohibits any depositional environment interpretation and any isopach mapping at geological stage level. If not, the carbonate platforms of different age would be amalgamated, without any connection with the reality. Over the time, paleogeographic maps show syn-sedimentary short wavelength deformations, more or less well expressed according to the local sedimentary context. During the Lias and the Dogger, three steps can be distinguished in the southern Paris Basin. Hettangian to Lower Aalenian, the progressive increase in accommodation drives to total immersion of the continental areas; the maximum of accommodation during the Middle Toarcian entails uniform sedimentary conditions. However, short wavelength deformations persist. The major accidents defining the isopic zones are mainly North-South oriented. Middle Aalenian to Middle Bathonian, isopic zones are contrasted, controlled by the North-South accidents but also the North West-South East ones ; the variable accommodation allowed the development of regional sedimentary gaps and shallow limestone progradations on a marly area (so called “Sillon marneux”) ; tectonics events correspond to the Tethyan and the North Sea riftings influences. Upper Bathonian to Upper Oxfordian, the North West-South East tectonics accidents are particularly active; this tectonic phase could be associated to the thermal event, described in the Paris Basin and announcing the Malm depositional environment.  相似文献   

14.
突变文库的构建是定向进化研究过程中一个关键步骤,主要利用天然存在的系统或者人工合成的分子技术来产生多样性核酸分子文库,为制备和筛选具有一定特性的蛋白酶、多肽、人工抗体等提供庞大的遗传基因库,也可用于合成生物学中相关基因元件的研究与筛选,为目标生物制品的高效工业化生产提供动力。随着对突变文库构建技术研究的日益深入,各种文库构建策略相继被开发出来,并在生物能源、生物化工、生物医药、生物试剂和食品工业等方面得到了广泛的应用。然而,定向进化中的文库构建策略多有不同,各种突变文库构建技术的核心方法也在不断创新。主要介绍近年来实验室中人工合成多样性文库的前沿技术,并对文库构建技术在自动化和智能化方向的发展进行了展望。  相似文献   

15.
Tick saliva: recent advances and implications for vector competence   总被引:13,自引:0,他引:13  
Abstract . Secretions of the tick salivary glands are essential to the successful completion of the prolonged feeding of these ectoparasites as well as the conduit by which most tick-borne pathogens are transmitted to the host. In ixodid ticks the salivary glands are the organs of osmoregulation, and excess water from the bloodmeal is returned via saliva into the host. Host blood must continue to flow into the feeding lesion as well as remain fluid in the tick mouthparts and gut. The host's haemostatic mechanisms are thwarted by various anti-platelet aggregatory, anticoagulatory and anti-vasoconstrictory factors in tick saliva. Saliva components suppress the immune and inflammatory response of the host permitting the ticks to remain on the host for an extended period of time and, adventitiously, enhancing the transmission and establishment of tick-borne pathogens. Over the years much work has been done on the numerous enzyme and pharmacological activities found in the tick saliva. The present article reviews the most recent work on salivary gland secretionith special emphasis on how they favour pathogen transmission.  相似文献   

16.
Two engraved rocks are situated 140 m from each other at an altitude of about 2250 m. One of them is called “female dancer”, and the other, “the Pleiads”, and both show a group of seven small pitted areas, of which one is smaller than the others and ‘ identified as the “Pleiads stellar cluster”, often depicted or mentioned during Antiquity and also throughout various historical periods.On each of these rocks, a large halberd, whose handle is oriented east-west, was traced along a natural fissure in the rock and engraved in the center of the composition. The “Pleiads stellar cluster” is represented on each of the two rocks beside the halberd : although situated to the west above the halberd blade on the “female dancer” rock, it is placed to the south and to the left of the halberd handle on “the Pleiads” rock. This difference may mark two distinct calendar data.The position of the different figures in the compositions illustrated on these two rocks, in particular inversions in the representation of some of them may indicate two distinct periods of the agricultural yearly cycle: on the rock called “female dancer”, the “heliacal raise” at summer's end, marking the beginning of the harvest and, on the rock called “the Pleiads”, the “heliacal setting”, just before winter, after the end of the harvest, when the rains soaks the ground and it is time to plow.  相似文献   

17.
We describe a new genus and species of the diatom family Stephanodiscaceae with light and scanning electron microscopy from Libo Small Hole, Libo County, Guizhou Province, China. Edtheriotia guizhoiana gen. & sp. nov. has striae across the valve face of varying lengths, and are composed of fine striae towards the margin and onto the mantle. Many round to stellate siliceous nodules cover the exterior of the valve. External fultoportulae opening are short tubes; the opening of the rimportula lacks a tube. Internally a hyaline rim is positioned near the margin. Marginal fultoportulae possess two arcuate opercles. Areolae have domed cribra on the valve face. Those near the margin do not open to the interior. One to three sessile to slightly‐raised rimportulae are placed on the valve face towards the margin; they do not terminate shortened striae towards the center of the valve. This suite of features distinguishes this group from other known genera in the Stephanodicaeae. Cyclotella shanxiensis is transferred to Edtheriotia, making the new combination E. shanxiensis (Xie & Qi) Kociolek et al. comb. nov. It differs from E. guizhoiana by the presence of open pores near the margin of the valve. Features of the new genus are compared and contrasted with others in the Family Stephanodiscaceae. The two species of the genus, unlike most in the family, are known only from rivers and ponds from China and Japan.  相似文献   

18.
In two experiments, the rhabditid nematode Phasmarhabditis hermaphrodita, a parasite of slugs, was cultured in vitro and applied as a drench to soil at four dose rates (3 108, 1 109, 3 109 and 1 1010 ha-1) 1 or 4 days before planting lettuce seedlings in a polythene tunnel. The effects of the four nematode doses on slug damage during the first 3 weeks after planting and on the numbers of slugs found within and below lettuce plants at harvest were measured. Results were then compared with untreated plots and with plots where methiocarb pellets were applied at the recommended field rate. In the first experiment, methiocarb pellets significantly reduced the percentage of plants damaged by slugs, but the nematode did not. In the second experiment, methiocarb pellets and the second highest dose of nematodes significantly reduced the percentage of plants damaged by slugs. The different effect of the nematode in the two experiments may have resulted from differences in the timing of nematode application and/or differences in the pattern of slug damage between experiments. At the end of the first experiment, the highest two doses of nematodes and methiocarb pellets had significantly reduced the number of slugs found within lettuce plants at harvest and on the soil surface below the plants. At the end of the second experiment, analysis of variance showed no significant effects of any treatment on slug numbers or biomass, but regression analysis showed significant negative relationships between nematode dose and total slug numbers, numbers of Arion ater agg. and biomass of Deroceras reticulatum. In both experiments, increasing nematode dose significantly reduced the numbers of slugs found contaminating the harvested lettuce. At the end of the second experiment, the mean weight of individuals of A. ater agg. increased with rising nematode dose.  相似文献   

19.
In the genus Gunnera , the species of subgenus Panke are unique in having large, triangular scales between the leaves on the rhizomes. The morphological significance of these scales has been extensively debated in the past. They have been interpreted as stipules, ligules, or cataphylls, with attempts made to identify homologous structures in representatives of the other subgenera. In the stoloniferous subgenus Misandra, the shoot apex is covered by a hoodlike structure, usually termed ochrea, generally considered homologous to the scales in Panke . Efforts to find similar structures in the remaining subgenera were unsuccessful. Due to the lack of a phylogenetic hypothesis, the homology of the scales has remained unresolved. In this study, the shoot apices of species from all subgenera were examined by light and scanning electron microscopy and the results interpreted in a phylogenetic context. The tip of the stolons in subgenera Pseudogunnera and Milligania carries two opposite cataphylls at the base of the new shoot. These are homologous to the ochrea in Misandra which is in turn homologous to the scales in Panke ; the latter are thus neither stipules nor ligules but cataphylls. The stems of subgenera Ostenigunnera and Gunnera have no similar structures. © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society, 2003, 142 , 301−308.  相似文献   

20.
The new analysis of the Middle Paleolithic industry from the cave Vindija (Croatia), showed a necessity of revision of the previous obtained data especially considering the use and origin of the raw materials (Kurtanjek and Marci, 1990). The results presented in this study pointed out some new aspects of interpretation. First, the significance of quartz in the Middle Paleolithic was underestimated. At the same time it is obvious that the major change in the use of the raw material was at the beginning of the Upper Paleolithic and of the Epigravettian, especially in the use of chert. The second change is registered in the use of chert between Middle and Upper Paleolithic: the chalky nodules of chert are more frequent in the Upper Paleolithic then the river pebbles used in the production of Middle Paleolithic artefacts. Still, the origin of this new raw material is at the moment unknown.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号