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31.
LL. Lloyd 《The Annals of applied biology》1943,30(4):358-364
The incidence of the sewage fly, Psychoda alternata Say, breeding almost free from other insect competitors in a bacteria bed at Huddersfield is examined. Its general seasonal trend is marked by periods of peak output explained on the theory that there are two successions of generations running persistently and alternating with one another. Such behaviour has previously been demonstrated for another sewage fly, Spaniotoma minima , and has been shown to be instituted by irregular temperatures in autumn and spring. In Psychoda alternata a special type of intraspecific competition is set-up in the warmer months when the cycles are rapid, for the larvae of one succession must start life in a bed just depleted of food by the other. Therefore large and small outbursts of the fly tend to alternate. The discharges of solids from the bed have a detailed periodicity corresponding to the alternations in the successions of the fly. 相似文献
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KARIN NORÉN ERS ANGERBJÖRN PÁLL HERSTEINSSON 《Biological journal of the Linnean Society. Linnean Society of London》2009,97(1):18-26
The genetic composition of a population reflects several aspects of the organism and its environment. The Icelandic Arctic fox population exceeds 8000 individuals and is comprised of both coastal and inland foxes. Several factors may affect within-population movement and subsequent genetic population structure. A narrow isthmus and sheep-proof fences may prevent movement between the north-western and central part and glacial rivers may reduce movement between the eastern and central part of Iceland. Moreover, population density and habitat characteristics can influence movement behaviour further. Here, we investigate the genetic structure in the Icelandic Arctic fox population ( n = 108) using 10 microsatellite loci. Despite large glacial rivers, we found low divergence between the central and eastern part, suggesting extensive movement between these areas. However, both model- and frequency-based analyses suggest that the north-western part is genetically differentiated from the rest of Iceland (FST = 0.04, DS = 0.094), corresponding to 100–200 generations of complete isolation. This suggests that the fences cannot be the sole cause of divergence. Rather, the isthmus causes limited movement between the regions, implying that protection in the Hornstrandir Nature Reserve has a minimal impact on Arctic fox population size in the rest of Iceland. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 97 , 18–26. 相似文献
34.
Toni Gabaldón Christophe Dessimoz Julie Huxley-Jones Albert J Vilella Erik LL Sonnhammer Suzanna Lewis 《Genome biology》2009,10(9):1-3
A report of the 24th International Conference on Yeast Genetics and Molecular Biology, Manchester, UK, 19-24 July 2009. 相似文献
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JM Rodríguez-Domínguez LL Ríos-Lara E Tapia-Campos R Barba-Gonzalez 《Biotechnic & histochemistry》2017,92(3):159-166
Preparations that contain well-spread metaphase chromosomes are critical for plant cytogenetic analyses including chromosome counts, banding procedures, in situ hybridization, karyotyping and construction of ideograms. Chromosome spreading is difficult for plants with large and numerous chromosomes. We report here a technique for obtaining cytoplasm-free, well-spread metaphases from two Amaryllidaceae species: Sprekelia formosissima (2n = 120) and Hymenocallis howardii (2n = 96). The technique has three main steps: 1) pretreatment to cause chromosome condensation, 2) dripping onto tilted slides coated with a thin layer of pure acetic acid and 3) application of steam and acetic acid to produce cytoplasmic hydrolysis, which spreads the chromosomes. 相似文献
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Uptake of CO2 by aquatic vegetation 总被引:15,自引:10,他引:5
Abstract Photosynthesis by aquatic plants based on the supply of CO2 from air-equilibrated solutions may be limited by the low diffusion coefficient of CO2 in water. For plants in which the transport of CO2 from the bulk medium is by diffusion, and the initial carboxylation uses RUBISCO, CO2 supply can be increased by growth in habitats with fast water flow over the surface (reducing unstirred layer thickness), or with heterotrophically-augmented CO2 levels, including the direct use of sediment CO2. Many aquatic plants using RUBISCO as their initial carboxylase counter the limitations on CO2 supply via the operation of biophysical CO2 concentrating mechanisms which are based on active transport of HCO?3, CO2 or H+ at the plasmalemma, and use bulk-phase HCO?3 or CO2 as the C source. A final group of aquatic plants use biochemical CO2 concentrating mechanisms based on auxiliary carboxylation by PEPc: C4-like and Crassulacean Acid Metabolism–like processes are involved. These various mechanisms for increasing CO2 supply to RUBISCO also help to offset the low specific reaction rate of aquatic plant RUBISCOs at low [CO2] and low [CO2]: [CO2]. In addition to overcoming restrictions on CO2 supply, the various methods of increasing inorganic C availability may also be important in alleviating shortages of nitrogen or photons. 相似文献
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Identification of sex in Cetaceans by multiplexing with three ZFX and ZFY specific primers 总被引:12,自引:0,他引:12
We sequenced 540 nucleotides of the last exon in the ZFY/ZFX gene in two males and two females for eight cetacean species; four odontocetes (toothed whales) and four mysticetes (baleen whales). Based upon the obtained nucleotide sequences, we designed two sets of oligonucleotide primers for specific amplification of the ZFX and the ZFY sequence in odontocetes and mysticetes, respectively. Each primer set consisted of three oligonucleotides; one forward-orientated primer, which anneals to the ZFY as well as the ZFX sequence, and two reverse-orientated primers that anneal to either the ZFX or the ZFY sequence. The resulting two amplification products (specific for the ZFY and ZFX sequences) can be distinguished by gel-electrophoresis through 2% NuSieve™. The accuracy of the technique was tested by determination of gender in 214 individuals of known sex. Finally we applied the technique to determine the sex of 3570 cetacean specimens; 2284 humpback whales, 315 fin whales, 37 blue whales, 7 minke whales, as well as 592 belugas, 335 narwhals and 25 harbour porpoises. 相似文献