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1.
T. Spencer T. G. Benton T. SPENCER 《Biological journal of the Linnean Society. Linnean Society of London》1995,56(1-2):13-42
The remote Pitcairn Group in the South Pacific Ocean comprises a volcanic island (Pitcairn Island), two low coral atolls (Oeno, Ducie) and a raised coralline island (Henderson Island). The geological history of these islands, on anomalously thin oceanic lithosphere, is related to the development of two subparallel island chains (Oeno-Henderson-Ducie; Pitcairn) associated with intra-Pacific plate 'hotspot' activity; the surface manifestation of this activity has been partly determined by structural lineations in the plate inherited from past plate history. The climate of the Pitcairn Islands is determined by the position of the subtropical high pressure system and the South Pacific Convergence Zone. Variations in the strength of this atmospheric circulation system, measured by changes in the Southern Oscillation index of pressure difference, provide a partial explanation of the long-term variability of mean annual rainfall at Pitcairn Island. Knowledge of past climates in the Pitcairn Group remains speculative. Maps of the Pitcairn Islands and a report of climate at Henderson Island (2/91-1/92) are included in the paper. 相似文献
2.
LINDA M. McINNES IAN R. DADOUR MEREDITH E. STEWART WILLIAM G. F. DITCHAM PETER MAWSON PETER B. S. SPENCER 《Molecular ecology resources》2005,5(3):504-506
Microsatellite loci were isolated from Carnaby's black cockatoo (Calyptorhynchus latirostris: Aves), a highly valued, endangered, and endemic species of bird from Western Australia. This study describes three dinucleotide and one tetranucleotide microsatellite loci for which the primers produced clear and polymorphic amplification patterns with between two and nine alleles and moderate levels of variability. Two additional dinucleotide markers which were monomorphic in the Carnaby's cockatoo were able to amplify and were polymorphic in two other species of black cockatoo, greatly increasing the utility of these markers. 相似文献
3.
Abstract Chenopodium album L. plants, grown under controlled environmental conditions on different levels of soil nitrate, produced seeds with proportionately different NO?3 contents. Regardless of the endogenous NO?3 content, few seeds germinated in water or upon treatment with KNO3. Ethylene promoted germination, and the extent of germination was positively correlated with the endogenous seed NO?3 content. Combined application of ethylene and KNO3 in the dark had a synergistic effect on NO?3 -deficient seed. The synergism between ethylene and KNO3 was attributable to the NO?3 moiety of the nitrate salt. Ethylene and light showed moderate synergism in seeds with low or high endogenous nitrate. Addition of nitrate, however, masked the interaction between ethylene and light. Gibberellic acid4+7 (GA4+7) or red light, each alone or combined with KNO3, had little effect on germination. When applied together in the dark, ethylene and GA4+7 synergistically enhanced the germination of NO?3-deficient seed. The combined effects of the two hormones on this seed were further enhanced by the addition of KNO3. There was no synergism between ethylene and GA4+7 in NO?3-rich seed. These interactions among GA4+7, ethylene and KNO3 were not affected by light. The results confirm and further elaborate our earlier finding that the sensitivity of C. album seeds to ethylene may depend on nitrate availability. 相似文献
4.
The fungitoxicity of 2-deoxy-D-glucose was examined in spore germination tests using Botrytis cinerea, B. fabae, Alternaria brassicicola, Aspergillus niger, Cladosporium cucumerinum, C. fulvum, Sclerotinia fructigena, Verticillium albo-atrum and Glomerella cingulata. It proved to be toxic, at concentrations below 10 μg./ml., to all of these fungi except G. cingulata which was resistant to concentrations up to 2000 μg./ml. The effect of a-deoxy-D-glucose on the mycelial growth of these fungi was assessed and again G. cingulata proved to be resistant to high concentrations of the compound, as also did A. niger.
The results are discussed in relation to the known inhibitory nature of 2-deoxy-D-glucose in other systems. 相似文献
The results are discussed in relation to the known inhibitory nature of 2-deoxy-D-glucose in other systems. 相似文献
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We compared the length of time parasitic and nonparasitic female birds spent on nests while laying eggs (laying bouts) to evaluate the hypothesis that rapid laving by parasitic Brown-headed Cowbirds Molothrus ater and other parasitic birds is a specialization for brood parasitism. Brown-headed Cowbirds typically spent less than 1 min on host nests while laying (41.0 ± 4.58 [mean ± s.e.] s, n = 21). In contrast, mean laving bouts of six nonparasitic icterine species ranged from 21.5 min to 53.4 min, and laying bouts of 13 other passerine species ranged from 20.7 min to 103.7 min. By spending only a few seconds on the nest while laying, brood parasites probably increase their chances of parasitizing nests unnoticed by hosts or, if noticed, are harassed by hosts for less time. Rapid laying may be adaptive if aggression by hosts can thwart attempted parasitism by chasing away the parasite, preventing the parasite from entering the nest or injuring the parasite. Rapid laying may increase the likelihood that the parasitic egg will be accepted. We tested some of these hypotheses by recording the responses of three frequently parasitized species to a stuffed female cowbird placed on their nests for 1 min. All species attacked the model vigorously; however, the mean time for discovery of the model ranged from 3 min to 17 min, ample time for female cowbirds to parasitize the nests. We concluded that rapid laying by parasitic birds is an adaptation for parasitism and, in Brown-headed Cowbirds, reduces the chances that the parasite will be attacked by hosts. 相似文献
9.
SPENCER H. HAMADA 《Development, growth & differentiation》1979,21(1):39-46
Disaggregated single cells from the gastrula of Strongylocentrotus purpuratus were studied as they reaggregated and reformed quasi-normal embryos. In this investigation emphasis was placed on the structural events involved during the reformation of cell contacts vis-a-vis cell migration. The early cell contacts are non-junctional cell appositions, which are characterized by non-parallel apposing membranes. Between post-migratory epithelial cells, there is a shift from non-parallel to parallel apposing membranes. These cell appositions are found between the overlapping lamellapodia along the apical margins of the epithelial cells during blastocoel enlargement. Incipient continuous junctions are formed by the deposition of an electron dense material in the intermembrane space. As the junction develops, electron dense plaques form in the cytoplasm immediately subjacent to the junction and septa form between the apposing membranes. 相似文献
10.
Iris M Costa Tallybia HT Nasser Marilene Demasi Rafaella MP Nascimento Luis ES Netto Sayuri Miyamoto Fernanda M Prado Gisele Monteiro 《BMC microbiology》2011,11(1):268