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1.
GEORGE THEOKRITOFF 《Lethaia: An International Journal of Palaeontology and Stratigraphy》1985,18(4):283-293
A model of Early Cambrian trilobite biogeography in the North Atlantic region (Theokritoff 1979. Lethaia 12 , 281–295) is reviewed and modified in the light of new data. The presence of Wanneria in conglomerates bearing the Elliptocephala asaphoides fauna strengthens correlation of the E. asaphoides fauna as well as, by implication, the upper part of the Calluvia Zone with the middle part of the Bonnia-Olenellus Zone. The faunas of the Bastion Formation of East Greenland and of the Devil's Cove Limestone of northern Newfoundland are reinterpreted as shelf faunas. Additional occurrences of Archaeocyatha are noted in Spain and northwest Scotland but reports of Archaeocyatha in northern Norway and East Germany are not authenticated. Neither Salterella nor 'Volborthella' are now recognized as characteristic of any trilobite province. Although Ordovician acritarch provinces show congruence with trilobite provinces, available data on Early Cambrian plankton are not sufficient to support algal provincialism. Interpretation of the geological record suggests that the Early Cambrian lapetus Ocean was stratified with a well-mixed oxygenated zone overlying a phosphate-rich oxygen minimum zone and that the Elliptocephala asaphoides fauna should be reinterpreted as a warm-water fauna. 相似文献
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GEORGE THEOKRITOFF 《Lethaia: An International Journal of Palaeontology and Stratigraphy》1979,12(4):281-295
Early Cambrian lithofacies and their stratigraphic context, characteristic of a number of tectonic elements within the North Atlantic region, are interpreted with respect to depositional environment and related trilobite provincialism. Faunas of the North American province are typically indigenous to shallow, warm water on a sand-carbonate shelf on the North American craton; those of the Scandian province to shallow cold water with predominantly clastic deposition on the European platform; those of the Avalonian province to shallow cold water with predominantly clastic deposition fringing islands and rises on the Iapetus Ocean floor; Intermediate zone faunas, consisting of North American, Avalonian and endemic elements, to the slope or margin of the North American shelf; faunas of the Tethyan province to a shelf bordering Gondwanaland ranging from warm to cold at different times and different places, and under some Avalonian influence in the later Early Cambrian; and a pelagic realm characterized by agnostids. Biogeographic boundaries are related to the position of the thermocline and to light regimen, which determines the biogeography of autotrophs and hence of provincial niche structure. Provincialism is determined by gross environmental differences reinforced by biotic factors. 相似文献
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Agnes Mols-Mortensen Christopher D. Neefus Poul Møller Pedersen Juliet Brodie 《欧洲藻类学杂志》2014,49(1):1-10
Greenland is a continental island in the northern part of the North Atlantic where the foliose Bangiales flora is poorly known. It is an important area for the study of algal biogeography because of the region’s glacial history, in which Greenland has been alternately exposed to or isolated from the North Pacific via the Bering Strait. A molecular study using 3′ rbcL + 5′ rbcL–S sequences was undertaken to assess the diversity of foliose Bangiales on the west coast of Greenland and rbcL sequences were used to study the Greenland flora in a larger phylogenetic and floristic context. New and historic collections document seven species in four genera from the west coast of Greenland. All species had a close link to North Pacific species, being either conspecific with them or North Atlantic–North Pacific vicariant counterparts. 相似文献
5.
Changing economies and patterns of trade, rather than climatic deterioration, could have critically marginalized the Norse Greenland settlements and effectively sealed their fate. Counter-intuitively, the end of Norse Greenland might not be symptomatic of a failure to adapt to environmental change, but a consequence of successful wider economic developments of Norse communities across North Atlantic. Data from Greenland, the Faroe Islands, and medieval Iceland is used to explore the interplay of Norse society with climate, environment, settlement, and other circumstances. Long term increases in vulnerability caused by economic change and cumulative climate changes sparked a cascading collapse of integrated interdependent settlement systems, bringing the end of Norse Greenland. 相似文献
6.
The maize landraces in the North East Himalayan (NEH) region in India, especially in the Sikkim state, are morphologically
highly diverse. The present study provides details of phenotypic and molecular characterization of a set of 48 selected maize
landrace accessions, including the ‘Sikkim Primitives’ which have a unique habit of prolificacy (5–9 ears on a single stalk).
Multi-location phenotypic evaluation of these 48 accessions revealed significant genetic variability for grain yield and its
components, leading to identification of several promising accessions. Cluster analysis and PCA using nine morpho-agronomic
characters clearly separated ‘Sikkim Primitives’ from the rest of the accessions. PCA revealed two principal components describing
90% of the total variation, with hundred kernel weight, ear length, ear diameter, number of kernels per ear and flowering
behaviour forming the most discriminatory traits. The accessions were genotyped using 42 microsatellite or simple sequence
repeat (SSR) markers using a ‘population bulk DNA fingerprinting strategy’, with allele resolution using an automated DNA
Sequencer. The study revealed a high mean number of alleles per SSR locus (13.0) and high Polymorphism Information Content
(PIC) value of 0.60. The analysis also led to identification of 163 private/unique alleles, differentiating 44 out of 48 accessions.
Six highly frequent SSR alleles were detected at different loci (phi014, phi062, phi090, umc1266, umc1367 and umc2250) with individual frequencies ≥0.75. Some of these SSR loci were reported to tag specific genes/QTL for some important traits,
indicating that chromosomal regions harboring these SSR alleles were not selectively neutral. Cluster analysis using Rogers’
genetic distance also revealed distinct genetic identity of the ‘Sikkim Primitives’ from the rest of the accessions in India,
including Sikkim. Mantel’s test revealed significant and positive correlation between the phenotypic and molecular genetic
dissimilarity matrices. The study was the first to portray the patterns of phenotypic and molecular diversity in the maize
landraces from the NEH region in India. 相似文献
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North winds and production in the eastern North Atlantic 总被引:9,自引:0,他引:9
Dickson R.R.; Kelly P.M.; Colebrook J.M.; Wooster W.S.; Cushing D.H. 《Journal of plankton research》1988,10(1):151-169
A long-term increase in northerly wind componentl over the easternNorth Atlantic and European Seaboard between 1950 and 1980 isassociated both with a decline of phytoplankton and zooplanktonbiomass in sea-areas around the British Isles, and with an increasein upwelling intensity along the Iberian west coast. The implicationsfor certain pelagic fish stocks in the area are assessed. 相似文献
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Oogenesis and the spawning pattern in Greenland halibut from the North-west Atlantic 总被引:1,自引:0,他引:1
Gametogenesis in Greenland halibut Reinhardtius hippoglossoides from the North-west Atlantic is not synchronous between individuals of the same population suggesting that the spawning season is not well defined. Differences in oocyte size–frequency distributions in prespawning, spawning and spent conditions suggest that Greenland halibut are capable of de novo vitellogenesis prior to and during spawning, indicating that the spawning pattern is not determinate. Greenland halibut may be capable of fast-tracking oocytes to maturity, whereby during the spawning season oocyte batches may be brought quickly through vitellogenesis so as to increase the fish's yearly reproductive output. 1999 The Fisheries Society of the British Isles 相似文献
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Gregory O’Corry-Crowe Christian Lydersen Mads Peter Heide-Jørgensen Lauren Hansen Lev M. Mukhametov Outi Dove Kit M. Kovacs 《Polar Biology》2010,33(9):1179-1194
Population structure in many Arctic marine mammal species reflects a dynamic interplay between physical isolating mechanisms
and the extent to which dispersal opportunities are met. We examined variation within mtDNA and eight microsatellite markers
to investigate population structure and demographic history in beluga whales in the North Atlantic. Genetic heterogeneity
was observed between Svalbard and West Greenland that reveals limited gene flow over ecological time scales. Differentiation
was also recorded between Atlantic belugas and two previously studied populations in the North Pacific, the Beaufort Sea and
Gulf of Alaska. However, Bayesian cluster analysis of the nDNA data identified two population clusters that did not correspond
to the respective ocean basins, as predicted, but to: (1) Arctic (Svalbard–White Sea–Greenland–Beaufort Sea) and (2) Subarctic
(Gulf of Alaska) regions. Similarly, the deepest phylogeographic signal was between the Arctic populations and the Gulf of
Alaska. Fitting an isolation-with-migration model yielded genetic abundance estimates that match census estimates and revealed
that Svalbard and the Beaufort Sea likely diverged 7,600–35,400 years ago but have experienced recurrent periods with gene
flow since then, most likely via the Russian Arctic during subsequent warm periods. Considering current projections of continued
sea ice losses in the Arctic, this study identified likely routes of future contact among extant beluga populations, and other
mobile marine species, which have implications for genetic introgression, health, ecology and behavior. 相似文献
14.
In laboratory experiments, bacterioplankton were incubated under different nutrient conditions, and the percentage of bacteria
exhibiting a polysaccharidic capsule (capsulated bacteria) and that of CTC (cyanotetrazolium chloride)-positive and therefore
metabolically highly active bacteria were determined. In these seawater cultures amended with nutrients more than 95% of the
CTC-positive cells exhibited a capsule. During two cruises, one to the North Atlantic and one to the North Sea, we investigated
the distribution of capsulated bacteria throughout the water column. Capsulated bacteria were generally more abundant in eutrophic
surface waters than in deeper layers or more oligotrophic regions. In the upper 100 m of the North Atlantic, about 6–14% of
the total bacterioplankton community was capsulated, while in the layers below 100 m depth, 97% of the bacteria lacked a visible
capsule. The percentage of capsulated bacteria correlated with bacterial abundance and production, and chlorophyll a concentration.
Also, the bioavailability of DOC (dissolved organic carbon), estimated by the ratio between bacterial production and DOC concentration,
significantly correlated with the percentage of capsulated bacteria. In the North Sea, the contribution of capsulated bacteria
to the total number of bacteria decreased from the surface (3 m depth) to the near-bottom (25–35 m) layers from 20% to 14%
capsulated bacteria. In the nearshore area of the North Sea, about 27% of the bacteria exhibited a capsule. Overall, a pronounced
decrease in the contribution of capsulated bacteria to the total bacterial abundance was detectable from the eutrophic coastal
environment to the open North Atlantic. Using this epifluorescence-based technique to enumerate capsulated bacterioplankton
thus allowed us to routinely assess the number of capsulated bacteria even in the oceanic water column. Based on the data
obtained in this study we conclude that almost all metabolically highly active bacteria exhibit a capsule, but also some of
the metabolically less active cells express a polysaccharide capsule detectable with this method. 相似文献
15.
Erkki Haukioja 《Ecography》1979,2(4):272-274
Birch forest on the slope of the Jesnalvaara fell forms a gradient ranging from 7–8 m high trees (at 75 m a.s.l.) to birch shrubs less than 1 m high at the top of the fell (330 m a.s.l.). Upper parts of the forest (above 220 m) were defoliated by Oporinia autumnata (Lep., Geometridae) about ten years ago and, with the exception of the top, only a fraction of birches have recovered. Climatic conditions explain the limitation of the damaged area – Oporinia eggs were killed during cold winters. Predators may also limit the damage. Defensive mechanisms in the birch leaves – especially a low nitrogen content and high concentrations of phenols inhibiting trypsin – can slow down an increase in herbivore density by reducing their reproductive capacity. Birch leaves from the lower limit of the damaged area are least suitable for the growth of herbivores. They have the highest concentration of phenols, too. Birches at the foot of Jesnalvaara are able to increase leaf phenols after mechanical damage of nearby leaves. This is enough to retard the growth of several herbivore species. Ability to recover after defoliation is an important part of the anti-herbivore strategy of the birch. This ability is higher in shrub birches than in tall trees and better after a warm than a cold summer. Birch leaves in the year following defoliation are less usable for herbivores and cause increased mortality and lowered reproduction. These properties are the weakest in birches at the foot of Jesnalvaara where the probability of being defoliated is also lowest. 相似文献
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Fellow travellers: a concordance of colonization patterns between mice and men in the North Atlantic region 总被引:1,自引:0,他引:1
EP Jones K Skirnisson TH McGovern MTP Gilbert E Willerslev JB Searle 《BMC evolutionary biology》2012,12(1):1-8
Background
In the Calvin cycle of eubacteria, the dephosphorylations of both fructose-1, 6-bisphosphate (FBP) and sedoheptulose-1, 7-bisphosphate (SBP) are catalyzed by the same bifunctional enzyme: fructose-1, 6-bisphosphatase/sedoheptulose-1, 7-bisphosphatase (F/SBPase), while in that of eukaryotic chloroplasts by two distinct enzymes: chloroplastic fructose-1, 6-bisphosphatase (FBPase) and sedoheptulose-1, 7-bisphosphatase (SBPase), respectively. It was proposed that these two eukaryotic enzymes arose from the divergence of a common ancestral eubacterial bifunctional F/SBPase of mitochondrial origin. However, no specific affinity between SBPase and eubacterial FBPase or F/SBPase can be observed in the previous phylogenetic analyses, and it is hard to explain why SBPase and/or F/SBPase are/is absent from most extant nonphotosynthetic eukaryotes according to this scenario.Results
Domain analysis indicated that eubacterial F/SBPase of two different resources contain distinct domains: proteobacterial F/SBPases contain typical FBPase domain, while cyanobacterial F/SBPases possess FBPase_glpX domain. Therefore, like prokaryotic FBPase, eubacterial F/SBPase can also be divided into two evolutionarily distant classes (Class I and II). Phylogenetic analysis based on a much larger taxonomic sampling than previous work revealed that all eukaryotic SBPase cluster together and form a close sister group to the clade of epsilon-proteobacterial Class I FBPase which are gluconeogenesis-specific enzymes, while all eukaryotic chloroplast FBPase group together with eukaryotic cytosolic FBPase and form another distinct clade which then groups with the Class I FBPase of diverse eubacteria. Motif analysis of these enzymes also supports these phylogenetic correlations.Conclusions
There are two evolutionarily distant classes of eubacterial bifunctional F/SBPase. Eukaryotic FBPase and SBPase do not diverge from either of them but have two independent origins: SBPase share a common ancestor with the gluconeogenesis-specific Class I FBPase of epsilon-proteobacteria (or probably originated from that of the ancestor of epsilon-proteobacteria), while FBPase arise from Class I FBPase of an unknown kind of eubacteria. During the evolution of SBPase from eubacterial Class I FBPase, the SBP-dephosphorylation activity was acquired through the transition ??from specialist to generalist??. The evolutionary substitution of the endosymbiotic-origin cyanobacterial bifunctional F/SBPase by the two light-regulated substrate-specific enzymes made the regulation of the Calvin cycle more delicate, which contributed to the evolution of eukaryotic photosynthesis and even the entire photosynthetic eukaryotes. 相似文献18.
Fernandez Emilio; Mara{macron}on Emilio; Harbour Derek S.; Pingree Robin D. 《Journal of plankton research》1994,16(12):1627-1644
Photosynthetic carbon metabolism and the biochemical compositionof late-winter phytoplankton assemblages in the eastern NorthAtlantic Ocean were studied during an oceanographic cruise carriedout in March 1992. Enhanced levels of phytoplankton biomassand primary production were linked to the subtropical front-AzoresCurrent (STF/AC) region. High values of the relative incorporationof carbon into proteins indicated that the phytoplankton wasgrowing at a rate close to the maximum growth rate. A very highpercentage of carbon was incorporated into the lipid fractionat southern latitudes, whereas incorporation into polysaccharidespeaked at the AC. In general, the biochemical composition ofparticulate matter reflected the observed patterns of photosynthatepartitioning. Latitudinal changes in phytoplankton species compositionaccounted for the geographical variability in 14C labellingpatterns. Turnover times of particulate matter estimated forthe STF/AC region were relatively low (35 days) and suggestedbalancedgrowth of the microplankton community over daily timescales. 相似文献
19.
High dispersal potential has maintained long-term population stability in the North Atlantic copepod Calanus finmarchicus 总被引:1,自引:0,他引:1
Provan J Beatty GE Keating SL Maggs CA Savidge G 《Proceedings. Biological sciences / The Royal Society》2009,276(1655):301-307
The cool-water copepod Calanus finmarchicus is a key species in North Atlantic marine ecosystems since it represents an important food resource for the developmental stages of several fish of major economic value. Over the last 40 years, however, data from the Continuous Plankton Recorder survey have highlighted a 70 per cent reduction in C. finmarchicus biomass, coupled with a gradual northward shift in the species's distribution, which have both been linked with climate change. To determine the potential for C. finmarchicus to track changes in habitat availability and maintain stable effective population sizes, we have assessed levels of gene flow and dispersal in current populations, as well as using a coalescent approach together with palaeodistribution modelling to elucidate the historical population demography of the species over previous changes in Earth's climate. Our findings indicate high levels of dispersal and a constant effective population size over the period 359,000-566,000 BP and suggest that C. finmarchicus possesses the capacity to track changes in available habitat, a feature that may be of crucial importance to the species's ability to cope with the current period of global climate change. 相似文献
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Apart from the possible, but unproven presence of some Irish hermits, the Norse colonizers of the Faroe Islands arrived in
an unsettled landscape around A.D. 800. The archipelago was essentially unwooded and rich in bird and marine life. The area of land suitable for settlement
and farming was relatively meagre and concentrated in coastal areas; inland areas were suitable for shielings (summer pasture)
and subsequently more extensive grazing (outfield) activities. Reconstruction of the settlement distribution has not been
a well-developed aspect of Faroese historical study. Using archaeological and documentary evidence, we are able to present
the first comprehensive distribution map of Norse settlement, which emphasizes an overwhelmingly coastal focus of considerable
density. Using historical (including place-names), archaeological, and environmental evidence, we examine the nature and organization
of the Viking (early Norse) and medieval (later Norse) settlement. Colonization and economic activity in the islands were
strongly influenced by topographic and ecological factors. This, along with social organization, was subject to influences
which may have derived, at least in part, from experiences in a Norwegian homeland. 相似文献