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131.
Experimental effects of elevated salinity on three benthic invertebrates in Pyramid Lake,Nevada 总被引:7,自引:7,他引:0
Salinity of Pyramid Lake increased from 3.7 to 5.5 between 1933 and 1980. Concern over future reductions in overall species richness prompted experiments to assess responses of dominant lake organisms to elevated salinity. Salinity tolerances of three important benthic invertebrates, Hyalella aztecta, Chironomus utahensis, and Heterocypris sp., were tested in controlled laboratory bioassays and also in a semi-natural environment consisting of large (47 m3) mesocosms.Densities of H. azteca in mesocosms were significantly lower at salinities of 8.0 and 11.0 compared with 5.6 controls in year one, but not in 8.5 salinity mesocosms in year two. The 96-h LC50 for H. azteca was high at 19.5. Short-term mortalities of C. utahensis were 100% at salinities of 13.3 and greater. Fifty-seven percent fewer larvae matured from third to fourth instar at 8.9 than at 5.5 salinity in 17 day subacute bioassays. Furthermore, larval chironomid densities and emergence of adults from mesocosms were significantly reduced at salinities of 8.0 and higher compared with controls. Mortality of Heterocypris sp. was 50% at a salinity of 18.6 in laboratory bioassays and populations in mesocosms ranged between 40 and 100% lower at salinities of 8.0 and 11.0 than in controls.Multiple generation mesocosm experiments indicated all three invertebrates were more sensitive to elevated salinity than results of short-term bioassays. Our studies suggest populations of these invertebrates may be reduced from present levels if Pyramid Lake's salinity were to double, although none are expected to be extirpated. Food habit shifts and reduced production of lake fishes are likely consequences of salinity-induced disruption in the benthic invertebrate forage base. 相似文献
132.
Consumption of leaf detritus by a stream shredder: Influence of tree species and nutrient status 总被引:8,自引:3,他引:5
Four species of riparian vegetation (alder, birch, willow and poplar) were fertilized with nitrogen, phosphorus, nitrogen
+ phosphorus, or no fertilizer (control). The resulting leaf detritus (leached but not microbially colonized) was offered
to a stream shredder, Hydatophylax variabilis (Trichoptera: Limnephilidae). In one experiment, shredder consumption of leaf detritus from different nutrient treatments
(within tree species) was compared, and in a second experiment, consumption of different tree species (within nutrient treatments)
was compared. Larvae preferred leaf detritus from nitrogen + phosphorus treatments (except in poplar where nitrogen treatment
was preferred). Alder was preferred over other tree species for all treatments. Chemical and physical analyses of leaf litter
showed differences between tree species and nutrient treatments in nutrient content, tannins and leaf toughness. Leaf consumption
by larvae was positively associated with nitrogen content and negatively associated with condensed tannin content. Species
composition and nutrient status of riparian vegetation may strongly influence detrital food webs in streams. 相似文献
133.
Laminin alters cell shape and stimulates motility and proliferation of murine skeletal myoblasts 总被引:13,自引:0,他引:13
Proliferating skeletal myoblasts show multiple specific responses to laminin, one of the major glycoprotein components of basement membranes. Using MM14Dy myoblasts, a myogenic cell strain derived from a normal adult mouse skeletal muscle, we show in this study that substrate-bound laminin but not other matrix proteins such as collagens or fibronectin specifically and rapidly induces the outgrowth of cell processes, resulting in bipolar, spindle-shaped cells. This effect is independent from the presence of collagens or serum, and was also observed in primary cultures of fetal mouse skeletal myoblasts. The outgrowth of cell processes on laminin is associated with a dramatic stimulation of cell motility: MM14 myoblasts migrate about five times faster on laminin than on fibronectin. In another series of experiments the effect of laminin and fibronectin on thymidine uptake and proliferation of myoblasts was tested. On top of a type I collagen substrate which was provided to ensure complete adhesion even at low doses of laminin or fibronectin, laminin stimulated myoblast proliferation and incorporation of [3H]thymidine in a dose-dependent manner. The stimulation is two- to threefold higher than on dishes coated with equivalent amounts of fibronectin and is observed both in the presence and in the absence of serum. These results suggest that laminin, a major component of the muscle basal lamina, may be actively involved in the development and regeneration of skeletal muscle. 相似文献
134.
The coexistence and coevolution of sexual and asexual species under resource competition are explored with three models: a nongenetic ecological model, a model including single locus genetics, and a quantitative-genetic model. The basic assumption underlying all three models is that genetic differences are translated into ecological differences. Hence if sexual species are genetically more variable, they will be ecologically more variable. Under classical competition theory, this increased ecological variability can, in many cases, be an advantage to individual sexual genotypes and to the sexual species as a whole. The purpose of this paper is to determine the conditions when this advantage will outway three disadvantages of sexuality: the costs of males, of segregation, and of the additive component of recombination. All three models reach similar conclusions. Although asexuality confers an advantage, it is much less than a two-fold advantage because minor increases in the overall species niche width of the sexual species will offset the reproductive advantage of the asexual species. This occurs for two reasons. First, an increase in species niche width increases the resource base of the sexual species. Second, to the extent that the increase in niche width is due to increased differences between individuals, a reduction in intraspecific competition will result. This is not to imply that the sexual species will always win. The prime conditions that enable sexual species to stably coexist with or even supplant an asexual sister species are:
- 相似文献
135.
Mark Tony Lieberman Robert M. Zablotowicz Naida P. Davis-Omholt 《Applied microbiology》1986,51(4):715-719
An improved method for antibiotic resistance recovery of Bradyrhizobium japonicum from soybean (Glycine max (L.) Merr.) nodules that is simple, time saving, and economical was developed. This technique involves the use of two 96-well microtiter plates as a multinodule sterilization chamber and a template and a third plate as a 16-point replicator constructed with steel nails affixed to the plate with epoxy cement. With this system a team of four technicians could type 3,000 nodules per day. This method was useful in assessing strain establishment and interstrain competition when one or more uniquely labeled strains of B. japonicum were inoculated onto either growth-room- or field-grown soybeans. Contamination was low and reproducibility across replicates approached the theoretical upper limit. Simplicity in design and use made this recovery method especially adaptable for field studies in which large numbers of nodules were required to provide a representative statistical sample offering good precision. 相似文献
136.
Mark Poth 《Applied microbiology》1986,52(4):957-959
A chemolithotrophic ammonium-oxidizing bacterium that was able to reduce 15NO2− to 15N2 (m/z 30) while oxidizing ammonium under conditions of oxygen stress was isolated from stream sediments. Energy was derived from ammonium oxidation, as evidence by growth, with CO2 serving as the sole C source. The organism was a gram-negative, motile, short rod that failed to grow either aerobically or anaerobically in heterotroph media. The organism was identified as a Nitrosomonas sp. 相似文献
137.
Caitilyn Allen Verlyn K. Stromberg Franzine D. Smith George H. Lacy Mark S. Mount 《Molecular & general genetics : MGG》1986,202(2):276-279
Summary We report the complementation of a genetic lesion in the genome of Erwinia carotovora subsp. carotovora (Ecc), a pathogenic bacterium that incites soft rot of plants. A Sau3AI genomic library of Ecc was constructed using the conjugal cosmid pLAFR-3 as a vector. Sixteen cosmid clones encoding various plant tissue-degrading enzymes were identified, including a proteolytic clone, five cellulolytic clones, and ten pectolytic clones. We detected a mutant of Ecc with no proteolytic activity following transposon mutagenesis with an unstable Tn5-carrying plasmid. Conjugal transfer of the protease-encoding cosmid to this mutant restored near-wildtype extracellular protease production. Further manipulation and study of genes encoding pathogenic determinants in Ecc will be possible using this system. 相似文献
138.
Adaptation to High-Intensity, Low-Wavelength Light among Surface Blooms of the Cyanobacterium Microcystis aeruginosa 总被引:2,自引:0,他引:2 下载免费PDF全文
Hans W. Paerl Patricia T. Bland N. Dean Bowles Mark E. Haibach 《Applied microbiology》1985,49(5):1046-1052
Natural populations of the nuisance bloom cyanobacterium Microcystis aeruginosa obtained from the eutrophic Neuse River, N.C., revealed optimal chlorophyll a-normalized photosynthetic rates and resistance to photoinhibition at surface photosynthetically active radiation (PAR) intensities. At saturating PAR levels these populations exhibited higher photosynthetic rates in quartz than in Pyrex vessels. Eucaryotic algal populations obtained from the same river failed to counteract photoinhibition. At saturating PAR levels, such populations generally yielded lower photosynthetic rates in quartz containers than they did in Pyrex containers. Cultivation of natural Microcystis populations under laboratory conditions led to physiologically distinct populations which had photoinhibitory characteristics similar to those of other cultured cyanobacterial and eucaryotic algae. Our findings indicate that (i) photosynthetic production among natural surface populations is best characterized and quantified in quartz rather than Pyrex incubation vessels; (ii) extrapolation of natural photoinhibitory trends from laboratory populations is highly subjective to culture and PAR histories and may yield contradictory results; and (iii) buoyant surface-dwelling populations, rather than exhibiting senescence, are poised at optimizing PAR utilization, thereby maintaining numerical dominance in eutrophic waters when physico-chemical conditions favor bloom formation. 相似文献
139.
Summary The partitioning of energy in three species of nematode, Paroigolaimella bernensis, Diplogasteritus nudicapitatus and Rhabditis curvicaudata, from a polysaprobic environment is considered. Temperature was shown to have a profound impact on the rate at which these organisms obtained food resources and on the partitioning of energy into growth, reproduction and maintenance. Declining temperature resulted in a reduction in energy consumption and in production and maintenance costs. Absorption efficiencies were relatively low, rarely exceeding 20% and lying on average between 5–15%. Net production efficiencies varied throughout the life-cycle, but attained maximum levels of 70–80%. Females achieved higher net production efficiency than males. The physiology and ecological implications are discussed. 相似文献
140.
Summary Several predictions of central place foraging theory were tested. As predicted, beavers foraged more selectively at increasing distance from the central place. With increasing distance from the river's edge, beavers cut fewer branches and deleted small branches from their diet. Large branches were favored at all distances, which differs from patterns observed in previous studies of beaver foraging. This difference, however, is expected and supports Schoener's (1979) predictions which are based on differences between provisioning costs and item size.The selective harvesting of branches predicted by foraging theory affects plant growth form and may influence plant reproductive patterns. High rates of branch removal caused cottonwoods to develop a shrubby architecture. The importance of selective branch choice by beavers on patterns of cottonwood reproduction (i.e., delayed sexual maturity and induced cloning) is discussed. 相似文献