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The dynamics and mechanical forces generated during burrowing in Polyphysia crassa (Annelida: Polychaeta) and Priapulus caudatus (Priapulida) were investigated. Both animals live in soft marine muds and burrow by utilizing a direct peristaltic wave alternating with a high internal pressure event which thrusts the anterior part of the body into the substratum. Forces generated during the various phases of a typical burrowing cycle were measured in animals moving beneath the natural substratum at 5±3 °C using electronic transducers and recorder. During 'head' advance Polyphysia generated 0.027 N, and during 'tail' advance 0.020 N, with peak internal pressures averaging 0.95 kPa (= 0.095 N/cm2 ). Force by Priapulus during head advance and tail advance was 0.081 N and 0.121 N, respectively, with peak internal pressures averaging 2.47 kPa (= 0.247 N/cm2 ). Polyphysia moves more slowly (0.24 cm/min) than does Priapulus (0.76 cm/min) and expends more energy on mass moved per unit distance. These force measurements during a burrowing cycle were used in place of respirometry as a basis for computation of net cost of transport (NCT) for each animal. NCT for Polyphysia was 635 J kg-1 m-1 and for Priapulus was 314Jkg-1 m-l . Cost of transport for all burrowing animals thus far investigated is high compared to swimming, running and flying. For soft-bodied invertebrates that live an entirely buried existence this high cost must be interpreted in the broader context of the adaptive value of infaunal life, especially protection against predation, and not as simply a means of moving about. 相似文献
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An ecological investigation of the Portneuf River, Idaho: a semiarid-land stream subjected to pollution 总被引:2,自引:0,他引:2
The Portneuf River (mean monthly discharge near mouth 1.4-15.4 m3/s) in southeastern Idaho, U.S.A., flows through an area of reduced precipitation (approx. 33 cm/year) and is dependent on underground aquifers and snowmelt runoff from the surrounding mountains for its water. The stream was examined at ten locations, distributed over its 156-km course, during the period 1967-1971. The Portneuf River is shown to have undergone a number of changes from its natural state as evidenced by alterations in water quality and the distribution of benthic invertebrates along the stream course. Of particular interest are changes brought about by the use of the stream for irrigation and by runoff from agricultural lands, factors whose effects are magnified by the semiarid conditions of the region and by poor soil-conservation practices. However, the stream also is affected by wastes from a sewage-treatment plant, phosphate-processing operations, and an assortment of scattered urban sources. Benthic invertebrates were collected during all four seasons by means of artificial substratum samplers and during summer and autumn by a qualitative dip-net technique. In general, the samplers were more effective in obtaining a representative picture ofthe fauna. However, neither procedure alone gave as much information as the combined results. The artificial substratum collections are not believed to be representative of the usual effects of stream devvatering by irrigation withdrawal in as much as the samplers provide refugia for the benthos during the periods of reduced habitat. 相似文献
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NaCl effects on 4-desmethylsterol composition of plasma-membrane-enriched preparations from citrus roots 总被引:1,自引:0,他引:1
T. J. DOUGLAS 《Plant, cell & environment》1985,8(9):687-692
Abstract The free 4-desmethylsterol composition of plasma-membrane-enriched preparations from white fibrous roots of Rangpur lime (Citrus reticulata var. austera hybrid?), Kharna khatta (C. kharna Raf.) and Etrog citron (C. medica L.) seedlings grown in the presence of 0, 50, or 100 mol m?3 NaCl for 28 d was quantitated by gas chromatography (GC) on analytical capillary (SE-54 fused silica) columns and the sterols were identified by combined gas chromatography-mass spectrometry (GC-MS). Only three 4-desmethylsterols were positively identified by GC-MS, viz. campesterol, stigmasterol and sitosterol. Cholesterol could not be positively identified in any of the membrane preparations. Campesterol levels were generally similar for all treatments and for all three genotypes, approximating 30% of the total free 4-desmethylsterol content of the plasma membranes. At all levels of salinity (0, 50 or 100 mol m?3 NaCl) sitosterol levels decreased in the order Rangpur lime > Kharna khatta > Etrog citron and stigmasterol levels decreased in the reverse order. The ratio of sitosterol to stigmasterol was highest in Rangpur lime and lowest in Etrog citron at each level of salinity and was reduced by salt treatment in all three genotypes. Salt-induced reductions in the ratio of ‘more planar’ to ‘less planar’ sterols correlated inversely with the accumulation of Cl? in the leaves of the three genotypes suggesting a role for plasma membrane sterols in the Cl? exclusion mechanism. A model relating sterol structure, membrane sterol composition and membrane permeability to Cl? exclusion ability in citrus is presented. 相似文献
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The activity of 5′-nucleotidase and ouabain-sensitive Na/K ATPase was determined in seven different mouse melanoma cell lines. Ouabain-sensitive Na/K ATPase activity was found in NP40-treated cell homogenates of all cell lines. However, 5′-nucleotidase activity was found in only one mouse melanoma cell line—JB/RH. The absence of expression of 5′-nucleotidase activity in the other six cell lines is not associated with pigmentation in melanoma cells, nor is the gene switched off in all transformed melanocytes of C57BL/6 origin. 相似文献
8.
Amyloplast Sedimentation in Shoot Statocytes having a Large, Central Vacuole: Further Interpretation from Electron Microscopy 总被引:2,自引:1,他引:1
The claim (Lawton, Juniper, and Hawes, 1986) that amyloplastssediment through the central vacuole of geostimulated shootstatocytes has been critically examined. As the result of ourTEM study of Taraxacum statocytes and from theoretical considerationsof amyloplast sedimentation, we conclude that it is possiblefor individual amyloplasts surrounded by a layer of tonoplast-boundedcytoplasm to travel occasionally through the vacuole, but unlikelythat the majority of the amyloplasts in a statocyte sedimentin this manner. We put forward a scheme for amyloplast movementin shoot statocytes which emphasizes the fluidity of the tonoplastmembrane. In this scheme, it is expected that most amyloplastssediment in peripheral cytoplasm down the statocyte cell wall,but amyloplasts may also, as they sediment, create or breaktransvacuolar strands, or move through already existing transvacuolarstrands, or fall through the vacuole while enclosed by somecytoplasm and tonoplast membrane. Finally, it is suggested thatthe tonoplast membrane may have been neglected as a membranesite for detection of the gravity stimulus through interactionwith sedimenting amyloplasts. Key words: Amyloplast sedimentation, statocytes, geotropism, Taraxacum officinale 相似文献
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RONALD M. YOSHIYAMA CLAY SASSAMAN 《Biological journal of the Linnean Society. Linnean Society of London》1993,50(4):275-294
We examined levels of allozymic variation in intertidal sculpins of the genera Oligocottus, Clinocottus and Artedius. Variability in these species, as assessed by the proportion of loci polymorphic and average heterozygosity per locus, was generally low but within the range of values observed for other fish groups. In reviewing the ecological and life-history attributes of these sculpins, we found only one outstanding correlate of allozyme variability–larger-bodied species tended to have lower levels of variation. Also, the level of heterozygosity was not related in any obvious way to historical/ evolutionary aspects such as position in phylogenetic trees or the inferred relative ages of species. Our study of a relatively well-defined lineage of fishes that co-occur in the same geographical region and in the same, or broadly similar, habitats, underscores the difficulty of detecting correlations between genetic variability and seemingly relevant ecological features of species. 相似文献
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