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1.
?Eumysops is a peculiar representative of the currently tropical family Echimyidae, which evolved in increasingly dry and cold Plio–Pleistocene environments of southern South America. The results of a systematic and stratigraphic review of the genus, and of phylogenetic analyses based on both morphology and a combined morphological–molecular dataset in the context of extant representatives, are presented here. Recognised diversity includes four previously described species plus a new one from the late Pliocene. These species form a well-supported monophyletic clade, sister to the late Miocene ?Pampamys and the extant Thrichomys. The position of ?Eumysops–?Pampamys–Thrichomys in a major clade including non-‘eumysopine’ echimyids constrains the traditional taxon Eumysopinae only to these three genera. Phylogeny and stratigraphic distribution of ?Eumysops species suggest an essentially cladogenetic evolutionary pattern. Beyond this, a gradual directional change, involving increase in size and in molar hypsodonty, is shown by ?Eumysops chapalmalensis as part of a late Pliocene faunal turnover interpreted as a local representation of the 2.5-Ma cooling global event. Distinctive skeletal and dental anatomy of ?Eumysops, including large orbits, shortened braincase, marked hypsodonty and postcranial specialisations, would be a result of its southern history related to a particular palaeoclimatic context. 相似文献
2.
Frances M. Slaney 《Dialectical Anthropology》1989,14(3):213-234
Frances M. Slaney is Professor of Anthropology at the University of Laval, Quebec. 相似文献
3.
Silvana Condemi 《Human Evolution》2006,21(3-4):251-259
Today, a number of European fossils are known which can be dated between 500,000 and 900,000 years ago. These remains provide
evidence of an early human settlement of Europe, which apparently predates the emergence of Neanderthals. However, the taxonomic
attribution of these fossils and their phylogenetic relationship to each other and to Neanderthals remains unclear. Evidence
for a direct phylogenetic relationship with Neanderthals or a discontinuity is not yet conclusive. The task is complicated
by the fact that the emergence of the Neanderthal population was not abrupt, but progressive. It is probable that the peopling
of Europe during the entire Pleistocene was unique and presented from its very origins an “endemic” (a cul-de-sac) character,
which may explain that the first traces of fossils in Europe illustrate particularities in comparison those from Africa and
from Asia. Further paleontological discoveries will be needed to redefine the status of these features and to improve our
understanding of human evolution in Europe. 相似文献
4.
Martin A. Erlandson 《中国病毒学》2009,24(5):458-469
Baculoviridae is a family of insect-specific DNA viruses that have been used as biological control agents for insect pest control. In most
cases these baculovirus control agents are natural field isolates that have been selected based on their infectivity and virulence.
The advent of molecular tools such as restriction endonucleases, targeted polymerase chain reaction and new DNA sequencing
strategies have allowed for efficient detection and characterization of genotypic variants within and among geographic and
temporal isolates of baculovirus species. It has become evident that multiple genotypic variants occur even within individual
infected larvae. Clonal strains of baculovirus species derived either by in vitro or in vivo approaches have been shown to vary with respect to infectivity and virulence. Many of the cell culture derived plague-purified
strains have deletions that interrupt egt expression leading to virus strains that kill infected hosts more quickly. As well, in vitro clones often involve larger genomic deletions with the loss of pif gene function, resulting in strains deficient for oral infectivity. There are an increasing number of baculovirus species
for which complete genome sequences are available for more than one strain or field isolate. Results of comparative analysis
of these strains indicated that hr regions and bro genes often mark “hot spots” of genetic variability between strains and of potential recombination events. In addition, the
degree of nucleotide polymorphisms between and within strains and their role in amino acid substitutions within ORFs and changes
in promoter motifs is also beginning to be appreciated. In this short review the potential mechanisms that generate and maintain
this genetic diversity within baculovirus populations is discussed, as is the potential role of genetic variation in host-pathogen
interactions. 相似文献
5.
Nonlinkage of major histocompatibility complex class I and class II loci in bony fishes 总被引:11,自引:10,他引:1
Sato A Figueroa F Murray BW Málaga-Trillo E Zaleska-Rutczynska Z Sültmann H Toyosawa S Wedekind C Steck N Klein J 《Immunogenetics》2000,51(2):108-116
In tetrapods, the functional (classical) class I and class II B loci of the major histocompatibility complex (Mhc) are tightly linked in a single chromosomal region. In an earlier study, we demonstrated that in the zebrafish, Danio rerio, order Cypriniformes, the two classes are present on different chromosomes. Here, we show that the situation is similar in
the stickleback, Gasterosteus aculeatus, order Gasterosteiformes, the common guppy, Poecilia reticulata, order Cyprinodontiformes, and the cichlid fish Oreochromis niloticus, order Perciformes. These data, together with unpublished results from other laboratories suggest that in all Euteleostei,
the classical class I and class II B loci are in separate linkage groups, and that in at least some of these taxa, the class II loci are in two different groups.
Since Euteleostei are at least as numerous as tetrapods, in approximately one-half of jawed vertebrates, the class I and class II
regions are not linked.
Received: 30 August 1999 / Revised: 20 October 1999 相似文献
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Maria Rita Palombo Maria Teresa Alberdi Beatriz Azanza Caterina Giovinazzo José Luis Prado Raffaele Sardella 《Evolutionary ecology》2009,23(4):569-589
The Plio–Pleistocene carnivores from the North-Western Mediterranean (Iberian and Italian peninsulas, and France) are analysed
in order to investigate whether their diversity over the last 5.3 Ma was influenced by disturbances of the physical environment.
Trends in species diversity over time were analysed in successive unequal time intervals, which were reassessed on the basis
of local biochronological schemes. By using a taxon-free characterisation, species were assigned to various ecological categories
in accordance with feeding and hunting behaviour, preferred habitat, and average body mass. Principal Component Analysis identified
the most important ecological variables in recognising changes among the carnivoran Faunal Complexes that characterised each
time interval. The results obtained support the hypothesis that some complex, though not always direct relationships exist
between environmental changes and shifts in the diversity of Carnivora (especially for forest dwelling carnivorans). However,
progressive changes in carnivoran guilds cannot be interpreted as merely a response to climate changes, because intrinsic
biotic control (changes in inter-specific and intra-specific competition) also plays an important role in modifying carnivoran
diversity. Therefore, climate change seems to trigger the various factors that contribute to the reconstruction of carnivoran
palaeocommunities.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
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10.
M. Missori M. Papi G. Maulucci G. Arcovito G. Boumis A. Bellelli G. Amiconi M. De Spirito 《European biophysics journal : EBJ》2010,39(6):1001-1006
Ischemic heart disease is the leading cause of serious morbidity and mortality in Western society. One of the therapeutic
approaches is based on the use of thrombolitic drugs that promote clot lysis. Even if the mechanisms leading to clot lysis
are not completely understood, it is widely accepted that they depend on the complex biochemical reactions that occur among
fibrin fibers and fibrinolitic agents, and by their ready diffusion into the fibers. Here we investigate the effects of specific
anions on the architecture of protofibrils within fibrin fibers in fibrin gels prepared in a para-physiological solution.
The results obtained through small-angle X-ray scattering (SAXS) demonstrate that the characteristic axial and longitudinal
repeat distances among protofibrils are strongly affected by the action of Cl− and F− anions. 相似文献
11.
Summary Active HCO
3
t-
secretion in the anterior rectal salt gland of the mosquito larva,Aedes dorsalis, is mediated by a 11 Cl–/HCO
3
–
exchanger. The cellular mechanisms of HCO
3
–
and Cl– transport are examined using ion- and voltage-sensitive microelectrodes in conjunction with a microperfused preparation which allowed rapid saline changes. Addition of DIDS or acetazolamide to, or removal of CO2 and HCO
3
–
from, the serosal bath caused large (20 to 50 mV) hyperpolarizations of apical membrane potential (V
a) and had little effect on basolateral potential (V
bl). Changes in luminal Cl– concentration alteredV
a in a repid, linear manner with a slope of 42.2 mV/decaloga
Cl
l
–. Intracellular Cl– activity was 23.5mm and was approximately 10mm lower than that predicted for a passive distribution across the apical membrane. Changes in serosal Cl– concentration had no effect onV
bl, indicating an electrically silent basolateral Cl– exit step. Intracellular pH in anterior rectal cells was 7.67 and the calculated
was 14.4mm. These results show that under control conditions HCO3 enters the anterior rectal cell by an active mechanism against an electrochemical gradient of 77.1 mV and exits the cell at the apical membrane down a favorable electrochemical gradient of 27.6 mV. A tentative cellular model is proposed in which Cl enters the apical membrane of the anterior rectal cells by passive, electrodiffusive movement through a Cl–-selective channel, and HCO
3
–
exits the cell by an active or passive electrogenic transport mechanism. The electrically silent nature of basolateral Cl– exit and HCO3 entry, and the effects of serosal addition of the Cl–/HCO3 exchange inhibitor, DIDS, on
and transepithelial potential (V
ic) suggest strongly that the basolateral membrane is the site of a direct coupling between Cl– and HCO
3
–
movements. 相似文献
12.
Haneen Sadick Inigo Fleischer Ulrich Goessler Karl Hörmann Maliha Sadick 《Chronobiology international》2013,30(2):357-364
Osler disease is an autosomal dominant disorder of the fibrovascular tissue characterized by arteriovenous malformations with multi‐systemic haemorrhages. Recurrent epistaxis is the predominant symptom in more than 90% of patients. Recent studies showed circadian and seasonal patterns in the onset of nosebleeds, similar to acute cardiovascular events, such as myocardial infarction and stroke. The aim of this study was to determine whether such patterns would also apply to the onset of epistaxis in patients with Osler disease. In all, 110 patients with Osler disease who were under treatment for recurrent epistaxis at the University Hospital of Mannheim were requested to complete a questionnaire addressing the intensity and frequency of epistaxis according to the classification of Bergler et al., as well as circadian and circannual rhythmicity in the occurrence of epistaxis according to visual analogue scales (VAS). More than half of the patients claimed to experience daily to weekly episodes of recurrent epistaxis. The occurrence of epistaxis showed a biphasic 24 h pattern, with a primary peak in the morning (05∶00–8∶00 h) and smaller secondary peaks in the evening (17∶00–20∶00 h and 21∶00–00∶00 h). No significant seasonal variation was found in the onset of epistaxis. However, a slight tendency, with a peak in winter months, was observed. Similar to other chronobiological studies on nosebleeds, this study showed that the 24 h pattern and seasonal tendency in the onset of epistaxis even applied to patients with Osler disease. Further investigations are necessary to determine the pathological mechanism underlying this phenomenon. 相似文献
13.
Adenine uptake in cultured Chinese hamster fibroblasts showed biphasic saturation kinetics. The transport system was highly specific for adenine and was competitively inhibited by adenosine. Utilizing mutant clones of Chinese hamster fibroblasts that have either reduced or negligible adenine phosphoribosyltransferase (APRT) activity, we found that (1) adenine was not accumulated against a concentration gradient in the absence of APRT activity and (2) after rapid initial uptake equal to that of the parent the rates of adenine accumulation found for the mutants correlated strongly with their residual APRT activities. Furthermore, using either artificially depressed phosphoribosylpyrophosphate pool size and APRT activities or the mutants with decreased APRT activity, we found that adenine transport was independent of phosphorylation by APRT. These studies suggest that adenine is transported as the free base by facilitated diffusion and is subsequently phosphorylated by APRT. 相似文献
14.
The human distal thumb phalanx from the earlier Upper Paleolithic of Ob?azowa Cave, southern Poland, exhibits features of its palmar surface that align it morphologically principally with early modern humans. These aspects include the configurations of the proximal palmar fossa, the flexor pollicis longus tendon insertion, the proximal margin of the palmar apical tuft, and especially its low ulnar deviation angle. If it is assumed that it possessed the pollical phalangeal length proportions of an early modern human, it would exhibit modest base and tuft breadths. However, given Late Pleistocene archaic-modern contrasts in relative pollical phalanx lengths, the isolated nature of the phalanx prevents secure assessment of its radioulnar interphalangeal articular and apical tuft hypertrophy. Similar constraints apply to the assessment of other Pleistocene Homo pollical phalanges. 相似文献
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The effect of the nitrogen source on nitrate reductase and nitrite reductase synthesis has been studied in several filamentous dinitrogen-fixing cyanobacteria belonging to the genera Anabaena, Nostoc and Calothrix. Nitrate and nitrite uptake were also studied. High levels of both nitrate reductase and nitrite reductase were found only in the presence of nitrate or nitrite, as long as ammonium was absent from the culture medium. On the other hand, whereas nitrate uptake is an active process, two components, diffusion of nitrous acid and active transport of nitrite, appear to contribute to nitrite uptake.Abbreviations DCCD
N,N-dicyclohexylcarbodiimide
- MOPS
3-(N-morpholino)propanesulfonic acid
- TES
N-tris(hydroxymethyl)methyl-2-aminoethane-sulfonic acid
- Tricine
N-tris(hydroxymethyl)methylglycine 相似文献
17.
《Journal of bryology》2013,35(3):160-172
AbstractPhylogenetic analyses have largely resolved generic and higher level relationships within the Polytrichopsida, enabling polarisation of characters and the identification of macro-evolutionary trends. Topologies show strong geographic patterning, with major groups having predominantly Northern or Southern Hemisphere distributions and some general morphologies having arisen independently on either side of the equator. While most cases of apparent convergence have been taxonomically visible due to sufficient higher-level characters being present to distinguish unrelated genera, convergent reduction may have resulted in conflation of similar gametophytic morphologies in classification. We present further evidence for the polyphyly of Oligotrichum DC. as currently circumscribed, showing how this morphology has probably arisen through reduction on multiple occasions to produce distinct lineages that have lacked taxonomic identity. We present a preliminary arrangement of the species currently recognised in Oligotrichum, accommodating selected Southern Hemisphere taxa in Itatiella G.L.Sm., and combining Atrichopsis compressa (Hook.f. & Wilson) G.L.Sm. and Oligotrichum tenuirostre (Hook.) A.Jaeger under Notoligotrichum G.L.Sm. For several species that clearly do not belong in Oligotrichum but remain of ambiguous affinity to other genera we avoid making new combinations, as ongoing combined molecular and morphological studies have considerable potential to elucidate their relationships in the near future. 相似文献
18.
Árni Einarsson Gerdur Stefánsdóttir Helgi Jóhannesson Jón S. Ólafsson Gísli Már Gíslason Isamu Wakana Gudni Gudbergsson Arnthor Gardarsson 《Aquatic Ecology》2004,38(2):317-348
Ecological features of Lake Myvatn and the outflowing River Laxá show a wide range of spatial and temporal variations. The physical division of the lake into three main basins and the variation in chemical composition and temperature of the artesian springs feeding this shallow productive lake have large spatial effects. Variation in groundwater characteristics depends on percolation time and proximity to geothermal sources. Variation in precipitation is evened out by the porous volcanic soil and bedrock and the spring-water discharge is therefore very stable. A pulse of volcanic activity in 1975–1984 (the Krafla Fires) heated the groundwater entering the North Basin of the lake and changed its chemistry. Although much reduced, these effects have not disappeared yet, but overall the impact of the volcanic activity on the biota seemed minimal. Recycling of nutrients through internal loading is important and occurs on various time scales. In winter, when the lake is ice-covered, the topmost 5-cm layer of sediment pore water has a hundredfold concentration of nutrients relative to the overlying lake water. The nutrients are released during the ice-free period by sediment resuspension, diffusion, bioturbation and recycling. In spring, resuspension events sometimes lead to spikes in dissolved phosphorus and nitrogen, but there is little evidence of any major desorption of nutrients from suspended particles during such events later in the summer. In contrast to the stable groundwater, the biota show more or less regular fluctuations with no straightforward correlation with external signals. The most prominent fluctuations, those of the chironomid Tanytarsus gracilentus seem to be driven by interactions between the species and its sediment resources. Fluctuations in other invertebrates could be a consequence of the Tanytarsus cycles due to the large impact this species has on the benthic environment of this detritus-driven ecosystem. Temporal variation in epibenthic chironomids and Cladocera translates into variable production of vertebrate predators (Arctic charr, Salvelinus alpinus, and ducks), body condition and mortality of fish and sometimes into return rates of migrating adult ducks. The waterfowl show large temporal variation on a centennial scale, e.g., the invasion of the tufted duck (Aythya fuligula) which arrived by the end of the 19th century and has by now outnumbered other species. Fluctuations of Cyanobacteria (Anabaena) and the fish Gasterosteus aculeatus (three-spined stickleback) harmonize with the cycles in the benthic community. Palaeolimnological studies indicate that primary production in the South Basin became increasingly benthic as the lake depth was reduced by sedimentation (around 2 mm year–1). Other trends include a decrease in Tanytarsus and Daphnia and an exponential increase in green algae (Cladophorales, Pediastrum) and associated organisms. 相似文献
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O. L. Kurbatova E. Yu. Pobedonostseva F. R. Gurgenova K. B. Bulaeva 《Russian Journal of Genetics》2012,48(10):1048-1054
Using the 2002 All-Russian population census data, the parameters of differential fertility as a component of natural selection (Crow??s indices) have been calculated for women of seven age cohorts of the seven most numerous ethnic groups of the Republic of Dagestan. It has been shown that in the population of Dagestan in the second half of the 20th century the intensities of two types of selection tended to decrease, viz., intragroup selection relaxed in each ethnic group due to considerable reduction of interfamily variance in fertility and intergroup selection relaxed due to reduction of interethnic differences in fertility. A reduction of the average number of offspring (k) was observed in all ethnic groups, suggesting the spread of birth regulation practices (abortion and contraception). Nevertheless, all Muslim groups (aboriginal Dagestan ethnic groups and Azerbaijanis) are still characterized by an extended pattern of reproduction (2.7 < k < 3.3); in Russians k = 2.1. Interethnic differentials in natural reproduction rates, along with migration processes, account for the dynamics of the ethnic composition and gene-pool structure of the population of the Republic of Dagestan. 相似文献