943 resultados para Quaternary Rainforest, Palaeoclimate, U-Th Dating, Megafauna, Australia


Relevância:

30.00% 30.00%

Publicador:

Resumo:

Mode of access: Internet.

Relevância:

30.00% 30.00%

Publicador:

Resumo:

Australia and the United States have been extremely close allies since World War II. The engagements in Afghanistan and Iraq have continued this tradition. Yet even before the bombings in Bali and the confrontation with Iraq, an important debate about the costs and benefits of the relationship with the United States was underway in Australia. At a number of levels—economic, political, and even strategic—increasing numbers of Australians were critically reassessing the relationship and questioning the supposed benefits. Recent events have accelerated this process and thrown the relationship into even starker relief. This paper argues that the increasingly unilateral nature of American economic and strategic policy is imposing major costs on even its most loyal allies, a situation that threatens to undermine the legitimacy of, and support for, U.S. hegemony.

Relevância:

30.00% 30.00%

Publicador:

Resumo:

Phylogeographic analyses of the fauna of the Australian wet tropics rainforest have provided strong evidence for long-term isolation of populations among allopatric refugia, yet typically there is no corresponding divergence in morphology. This system provides an opportunity to examine the consequences of geographic isolation, independent of morphological divergence, and thus to assess the broader significance of historical subdivisions revealed through mitochondrial DNA phylogeography. We have located and characterized a zone of secondary contact between two long isolated (mtDNA divergence > 15%) lineages of the skink Carlia rubrigularis using one mitochondrial and eight nuclear (two intron, six microsatellite) markers. This revealed a remarkably narrow (width < 3 km) hybrid zone with substantial linkage disequilibrium and strong deficits of heterozygotes at two of three nuclear loci with diagnostic alleles. Cline centers were coincident across loci. Using a novel form of likelihood analysis, we were unable to distinguish between sigmoidal and stepped cline shapes except at one nuclear locus for which the latter was inferred. Given estimated dispersal rates of 90-133 m x gen(-1/2) and assuming equilibrium, the observed cline widths suggest effective selection against heterozygotes of at least 22-49% and possibly as high as 70%. These observations reveal substantial postmating isolation, although the absence of consistent deviations from Hardy-Weinberg equilibrium at diagnostic loci suggests that there is little accompanying premating isolation. The tight geographic correspondence between transitions in mtDNA and those for nuclear genes and corresponding evidence for selection against hybrids indicates that these morphologically cryptic phylogroups could be considered as incipient species. Nonetheless, we caution against the use of mtDNA phylogeography as a sole criterion for defining species boundaries.

Relevância:

30.00% 30.00%

Publicador:

Resumo:

In order to investigate population history and demography in skinks endemic to the wet tropics of Australia, multiple nuclear DNA markers were sought. The utility of 72 primers (including 63 published intron-spanning 'CATS' primers) was tested.. Seven loci were characterized and shown to be single copy by single-strand conformation polymorphism analysis. Primers to five nuclear loci were developed, four with utility in skinks and three with utility in frogs. These observations extend the available information on intron-spanning primers for amphibians and reptiles.

Relevância:

30.00% 30.00%

Publicador:

Resumo:

The phylogenetic relationships and historical biogeography of 10 currently described rainforest skinks in the genus Saproscincus were investigated using mitochondrial protein-coding ND4 and ribosomal RNA 16S genes. A robust phylogeny is inferred using both maximum likelihood and Bayesian analysis, with all inter-specific nodes strongly supported when datasets are combined. The phylogeny supports the recognition of two major lineages (northern and southern), each of which comprises two divergent clades. Both northern and southern lineages have comparably divergent representatives in mid-east Queensland (MEQ), providing further molecular evidence for the importance of two major biogeographic breaks, the St. Lawrence gap and Burdekin gap separating MEQ from southern and northern counterparts respectively. Vicariance associated with the fragmentation and contraction of temperate rainforest during the mid-late Miocene epoch underpins the deep divergence between morphologically conservative lineages in at least three instances. In contrast, one species, Saproseincus oriarus, shows very low sequence divergence but distinct morphological and ecological differentiation from its allopatric sister clade within Saproseincus mustelinus. These results suggest that while vicariance has played a prominent role in diversification and historical biogeography of Saproscincus, divergent selection may also be important. (C) 2004 Elsevier Inc. All rights reserved.

Relevância:

30.00% 30.00%

Publicador:

Resumo:

Sequence diversity in the coat protein coding region of Australian strains of Johnsongrass mosaic virus (JGMV) was investigated. Field isolates were sampled during a seven year period from Johnsongrass, sorghum and corn across the northern grain growing region. The 23 isolates were found to have greater than 94% nucleotide and amino acid sequence identity. The Australian isolates and two strains from the U.S.A. had about 90% nucleotide sequence identity and were between 19 and 30% different in the N-terminus of the coat protein. Two amino acid residues were found in the core region of the coat protein in isolates obtained from sorghum having the Krish gene for JGMV resistance that differed from those found in isolates from other hosts which did not have this single dominant resistance gene. These amino acid changes may have been responsible for overcoming the resistance conferred by the Krish gene for JGMV resistance in sorghum. The identification of these variable regions was essential for the development of durable pathogen-derived resistance to JGMV in sorghum.

Relevância:

30.00% 30.00%

Publicador:

Resumo:

Monoculture plantations of Pinus, Eucalyptus and Acacia have been established oil rainforest lands throughout the world. However, this type of reforestation generally supplies low quality timber and contributes to landscape simplification. Alternatives to exotic monoculture plantations are now beginning to gain momentum with farmers and landholders attempting to establish a variety of rainforest trees in small plantations. When compared to the well studied commercial species, knowledge concerning the growth and management of many of these rainforest species is in its infancy. To help expand this limited knowledge base an experimental plantation of 16 rainforest tree species in a randomised design was established near Mt. Mee, in south-eastern Queensland, Australia. Changes in growth, form (based on stem straightness, branch size and branchiness), crown diameters and leaf area of each species were examined over 5 years. Patterns of height growth were also measured monthly for 31 months. Species in this trial could be separated into three groups based on their overall growth after 5 years and their growth patterns. Early successional status, low timber density, high maximum photosynthetic rates and large total leaf areas were generally correlated to rapid height growth. Several species (including Araucaria cunninghamii, Elaeocarpus grandis, Flindersia brayleyana, Grevillea robusta and Khaya nyasica) had above average form and growth, while all species in the trial had considerable potential to have increased productivity through tree selection. As canopy closure occurred at the site between years four and five, growth increments declined. To reduce stand competition a number of different thinning techniques could be employed. However, simple geometric or productivity based thinnings appear to be inappropriate management techniques for this mixed species stand as they would either remove many of the best performing trees or nearly half the species in the trial. Alternatively, a form based thinning would maintain the site's diversity, increase the average form of the plantation and provide some productivity benefits.

Relevância:

30.00% 30.00%

Publicador:

Resumo:

Mechanisms of pollen transport in the humid tropics region of northeastern Australia were investigated to support the interpretation of a long Quaternary pollen record from ODP Site 820 located on the adjacent continental slope. Pollen analysis of surface sediment samples from the channels of two major river catchments demonstrated internal consistency in pollen spectra and little fluvial pollen sorting in relation to sediment variation. Differences in modem pollen spectra between catchments reflect existing variation in vegetation cover that, in turn, reflects climatic differences between catchments. Recent pollen spectra from top samples of the ODP core have sufficient in common with the riverine samples to suggest that the rivers are contributing a major pollen component to the offshore sediments, but these have been size sorted by marine action. Recent pollen samples from core tops taken from the Grafton Passage on the continental shelf that was thought to be the major passage for pollen transport to ODP Site 820 show significant differences to both riverine and ODP samples and suggest that pollen are dispersed across the continental shelf and through the outer Great Barrier Reef system in a more complex way than anticipated. (c) 2004 Elsevier B.V. All rights reserved.

Relevância:

30.00% 30.00%

Publicador:

Resumo:

We present new major element, trace element and Nd-isotope data for 30 alluvial sediments collected from 25 rivers in Queensland, E Australia. Samples were chosen to represent drainage from the region's most important lithologies, including Tertiary intraplate volcanic rocks, a Cretaceous igneous province (and sedimentary rocks derived thereof) as well as Proterozoic blocks. In most chemical and isotopic aspects, the alluvial sediments represent binary or ternary mixing relationships, with absolute abundances implied to reflect the proportion of lithologies in the catchments. When averaged, the studied sediments differ from other proxies of upper continental crust (UCC) mainly in their relative middle rare earth element enrichment (including an elevated Sm/Nd ratio), higher relative Eu abundance and higher Nb/Ta ratio. These features are inherited from eroded Tertiary intraplate basalts, which commonly form topographic highs in the studied region. Despite the high degree of weathering strong to excellent coherence between similarly incompatible elements is found for all samples. From this coherence, we suggest revisions of the following upper crustal element ratios: Y/Ho = 26.2, Yb/Tm = 6.37, Th/W = 7.14, Th/Tl = 24 and Zr/Hf = 36.9. Lithium, Rb, Cs and Be contents do not seem depleted relative to UCC, which may reflect paucity of K-feldspar in the eroded catchments. Nickel, Cr, Pb, Cu and Zn concentrations are elevated in polluted rivers surrounding the state capital. River sediments in the Proterozoic Georgetown Inlier are elevated in Pb, Cu and Zn but this could be a natural phenomenon reflecting abundant sulphide mineralisation in the area. Except for relative Sr concentrations, which broadly anticorrelate with mean annual rainfall in catchments, there is no obvious relationship between the extent of weathering and climate types, which range from and to tropical. The most likely explanation for this observation is that the weathering profiles in many catchments are several Myr old, established during the much wetter Miocene period. The studied sediment compositions (excluding those from the Proterozoic catchments) are used to propose a new trace element normalisation termed MUQ (MUd from Queensland), which serves as an alternative to UCC proxies derived from sedimentary rocks. Copyright (C) 2005 Elsevier Ltd

Relevância:

30.00% 30.00%

Publicador:

Resumo:

Staphylococcus aureus bacteremia (SAB) is common and increasing worldwide. A retrospective review was undertaken to quantify the number of cases, their place of acquisition, and the proportions caused by methicillin-resistant.S. aureus (MRSA) in 17 hospitals in Australia. Of 3,192 episodes, 1,571 (49%) were community onset. MRSA caused 40% of hospital-onset episodes and 12% of community-onset episodes. The median rate of SAB was 1.48/1,000 admissions (range 0.61-3.24; median rate for hospital-onset SAB was 0.7/1,000 and for community onset 0.8/1,000 admissions). Using these rates, we estimate that approximate to 6,900 episodes of SAB occur annually in Australia (35/100,000 population). SAB is common, and a substantial proportion of cases may be preventable. The epidemiology is evolving, with > 10% of community-onset SAB now caused by MRSA. This is an emerging infectious disease concern and is likely to impact on empiric antimicrobial drug prescribing in suspected cases of SAB.

Relevância:

30.00% 30.00%

Publicador:

Resumo:

A cyanogenic glycoside -6'-O-galloylsambunigrin - has been isolated from the foliage of the Australian tropical rainforest tree species Elaeocarpus sericopetalus F. Muell. (Elaeocarpaceae). This is the first formal characterisation of a cyanogenic constituent in the Elaeocarpaceae family, and only the second in the order Malvales. 6'-O-galloylsambunigrin was identified as the principal glycoside, accounting for 91% of total cyanogen in a leaf methanol extract. Preliminary analyses indicated that the remaining cyanogen content may comprise small quantities of sambunigrin, as well as di- and tri-gallates of sambunigrin. E. sericopetalus was found to have foliar concentrations of cyanogenic glycosides among the highest reported for tree leaves, up to 5.2 mg CN g(-1) dry wt. (c) 2006 Elsevier Ltd. All rights reserved.

Relevância:

30.00% 30.00%

Publicador:

Resumo:

A recent preliminary survey revealed that 12 species of unstalked crinoids occur on a gentle sandy slope (12-18 m depth) at Lizard Island, Great Barrier Reef, Australia; five of which are also found on coral reefs. The other seven appear to constitute a unique assemblage restricted to unconsolidated substrates, where most cling to algae or hide beneath rubble or sponges. Members of this assemblage exhibit all of the basic feeding postures found among reef-dwelling species. However, Comatula rotalaria, which lacks anchoring cirri and bears uniquely differentiated short and long arms, exhibits a posture different from other living crinoids. Quantitative transects reveal apparent depth-related differences in species composition: C. rotalaria dominated the 12 transects in 12-13 m (84% of 82 specimens), while Comatella nigra, Comatula cf. purpurea, Amphimetra cf. tessellata and Zygometra microdiscus accounted for 96% of 54 specimens observed along 12 transects in 16-17 m.

Relevância:

30.00% 30.00%

Publicador:

Resumo:

To explore the evolutionary consequences of climate-induced fluctuations in distribution of rainforest habitat we contrasted demographic histories of divergence among three lineages of Australian rainforest endemic skinks. The red-throated rainbow skink, Carlia rubrigularis, consists of morphologically indistinguishable northern and southern mitochondrial DNA (mtDNA) lineages that are partially reproductively isolated at their parapatric boundary. The third lineage (C. rhomboidalis) inhabits rainforests just to the south of C. rubrigularis, has blue, rather than red-throated males, and for mtDNA is more closely related to southern C. rubrigularis than is northern C. rubrigularis. Multigene coalescent analyses supported more recent divergence between morphologically distinct lineages than between morphologically conservative lineages. There was effectively no migration and therefore stronger isolation between southern C. rubrigularis and C. rhomboidalis, and low unidirectional migration between morphologically conservative lineages of C. rubrigularis. We found little or no evidence for strong differences in effective population size, and hence different contributions of genetic drift in the demographic history of the three lineages. Overall the results suggest contrasting responses to long-term fluctuations in rainforest habitats, leading to varying opportunities for speciation.