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971.
Eric P. Palkovacs Michael C. Marshall Brad A. Lamphere Benjamin R. Lynch Dylan J. Weese Douglas F. Fraser David N. Reznick Catherine M. Pringle Michael T. Kinnison 《Philosophical transactions of the Royal Society of London. Series B, Biological sciences》2009,364(1523):1617-1628
Evolution has been shown to be a critical determinant of ecological processes in some systems, but its importance relative to traditional ecological effects is not well known. In addition, almost nothing is known about the role of coevolution in shaping ecosystem function. Here, we experimentally evaluated the relative effects of species invasion (a traditional ecological effect), evolution and coevolution on ecosystem processes in Trinidadian streams. We manipulated the presence and population-of-origin of two common fish species, the guppy (Poecilia reticulata) and the killifish (Rivulus hartii). We measured epilithic algal biomass and accrual, aquatic invertebrate biomass, and detrital decomposition. Our results show that, for some ecosystem responses, the effects of evolution and coevolution were larger than the effects of species invasion. Guppy evolution in response to alternative predation regimes significantly influenced algal biomass and accrual rates. Guppies from a high-predation site caused an increase in algae relative to guppies from a low-predation site; algae effects were probably shaped by observed divergence in rates of nutrient excretion and algae consumption. Rivulus–guppy coevolution significantly influenced the biomass of aquatic invertebrates. Locally coevolved populations reduced invertebrate biomass relative to non-coevolved populations. These results challenge the general assumption that intraspecific diversity is a less critical determinant of ecosystem function than is interspecific diversity. Given existing evidence for contemporary evolution in these fish species, our findings suggest considerable potential for eco-evolutionary feedbacks to operate as populations adapt to natural or anthropogenic perturbations. 相似文献
972.
Zhongping Deng Lisa A. Dailey Joleen Soukup Jacqueline Stonehuerner Judy D. Richards Kimberly D. Callaghan Funmei Yang Andrew J. Ghio 《Biometals》2009,22(5):803-815
Despite recurrent exposure to zinc through inhalation of ambient air pollution particles, relatively little information is
known about the homeostasis of this metal in respiratory epithelial cells. We describe zinc uptake and release by respiratory
epithelial cells and test the postulate that Zn2+ transport interacts with iron homeostasis in these same cells. Zn2+ uptake after 4 and 8 h of exposure to zinc sulfate was concentration- and time-dependent. A majority of Zn2+ release occurred in the 4 h immediately following cell exposure to ZnSO4. Regarding metal importers, mRNA for Zip1 and Zip2 showed no change after respiratory epithelial cell exposure to zinc while
mRNA for divalent metal transporter (DMT)1 increased. Western blot assay for DMT1 protein supported an elevated expression
of this transport protein following zinc exposure. RT-PCR confirmed mRNA for the metal exporters ZnT1 and ZnT4 with the former
increasing after ZnSO4. Cell concentrations of ferritin increased with zinc exposure while oxidative stress, measured as lipid peroxides, was decreased
supporting an anti-oxidant function for Zn2+. Increased DMT1 expression, following pre-incubations of respiratory epithelial cells with TNF-α, IFN-γ, and endotoxin, was
associated with significantly decreased intracellular zinc transport. Finally, incubations of respiratory epithelial cells
with both zinc sulfate and ferric ammonium citrate resulted in elevated intracellular concentrations of both metals. We conclude
that exposure to zinc increases iron uptake by respiratory epithelial cells. Elevations in cell iron can possibly affect an
increased expression of DMT1 and ferritin which function to diminish oxidative stress. Comparable to other metal exposures,
changes in iron homeostasis may contribute to the biological effects of zinc in specific cells and tissues. 相似文献
973.
974.
Hyphal growth of Candida albicans is characterized by asymmetric cell divisions in which the subapical mother cell inherits most of the vacuolar space and becomes cell cycle arrested in G1, while the apical daughter cell acquires most of the cell cytoplasm and progresses through G1 into the next mitotic cell cycle. Consequently, branch formation in hyphal compartments is delayed until sufficient cytoplasm is synthesized to execute the G1 'START' function. To test the hypothesis that this mode of vacuole inheritance determines cell cycle progression and therefore the branching of hyphae, eight tetracycline-regulated conditional mutants were constructed that were affected at different stages of the vacuole inheritance pathway. Under repressing conditions, vac7 , vac8 and fab1 mutants generated mycelial compartments with more symmetrically distributed vacuoles and increased branching frequencies. Repression of VAC1 , VAM2 and VAM3 resulted in sparsely branched hyphae, with large vacuoles and enlarged hyphal compartments. Therefore, during hyphal growth of C. albicans the cell cycle, growth and branch formation can be uncoupled, resulting in the investment of cytoplasm to support hyphal extension at the expense of hyphal branching. 相似文献
975.
Tal Isaacson Dylan K. Kosma Antonio J. Matas Gregory J. Buda Yonghua He Bingwu Yu Arika Pravitasari James D. Batteas Ruth E. Stark Matthew A. Jenks Jocelyn K. C. Rose 《The Plant journal : for cell and molecular biology》2009,60(2):363-377
Plant cuticles are broadly composed of two major components: polymeric cutin and a mixture of waxes, which infiltrate the cutin matrix and also accumulate on the surface, forming an epicuticular layer. Although cuticles are thought to play a number of important physiological roles, with the most important being to restrict water loss from aerial plant organs, the relative contributions of cutin and waxes to cuticle function are still not well understood. Tomato ( Solanum lycopersicum ) fruits provide an attractive experimental system to address this question as, unlike other model plants such as Arabidopsis, they have a relatively thick astomatous cuticle, providing a poreless uniform material that is easy to isolate and handle. We identified three tomato mutants, cutin deficient 1 ( cd1 ), cd2 and cd3 , the fruit cuticles of which have a dramatic (95–98%) reduction in cutin content and substantially altered, but distinctly different, architectures. This cutin deficiency resulted in an increase in cuticle surface stiffness, and in the proportions of both hydrophilic and multiply bonded polymeric constituents. Furthermore, our data suggested that there is no correlation between the amount of cutin and the permeability of the cuticle to water, but that cutin plays an important role in protecting tissues from microbial infection. The three cd mutations were mapped to different loci, and the cloning of CD2 revealed it to encode a homeodomain protein, which we propose acts as a key regulator of cutin biosynthesis in tomato fruit. 相似文献
976.
Wild tomatoes occur in habitats from the extremely dry Atacama Desert to moist areas in the Andean highlands, which may have resulted in adaptation of populations or species to differences in soil moisture availability. However, when two accessions representing extremes in habitat water availability from each of the five self-compatible species were grown in a common garden, we observed no differences in leaf physiological responses to soil drought within or between species. All five species had drought avoidance characteristics with the same threshold soil moisture availability for decline of assimilation, stomatal conductance, and leaf water potential (Ψ(l)) in response to slowly decreasing soil moisture. After rewatering, all species rapidly recovered to near predrought Ψ(l), but bulk leaf solute potential after recovery did not indicate any osmotic adjustment. The lack of variation in shoot physiological traits during soil drought is unexpected as water deficit is commonly thought to have imposed selective pressure in the evolution of plant physiology. However, species did differ in assimilation under nonstressed conditions, which may contribute to differential soil water conservation and growth or survival during drought. 相似文献
977.
978.
979.
Mehmet Uygur James G. Richards Slobodan Jaric Paulo B. de Freitas David A. Barlow 《Journal of biomechanics》2009,42(9):1241-1245
Most hip fractures are thought to occur after falling during everyday activities. We speculated that hip fractures might also occur because of excessive loading of the hip joint during an unexpected misstep consequently leading to a fall. The aims of this study were to explore the kinematics and kinetics of the lower extremity joints during missteps as compared with regular stepping, as well as to compare the magnitude of forces acting upon the hip joint with the threshold forces expected to fracture the hip. Fourteen healthy adults performed two forward steps on a 17.8 cm high platform under the following four conditions: forward with and without vision, as well as a misstep (the box for the final step unexpectedly removed without participant awareness), and regular stepping down with eyes open. The results revealed no differences between stepping forward with and without vision. When compared with both stepping forward and regular stepping down, the misstep revealed altered joint positions accompanied by increased forces and moments acting upon the hip joint. For example, the peak vertical proximal thigh segment force was 3.05±0.55 BW vs. 1.23±0.14 BW and 0.91±0.09 BW (p<.001; misstep vs. regular stepping down and stepping forward, respectively), while the proximal thigh segment moment in frontal plane was 1.39±0.70 Nm/kg vs. 0.18±0.32 Nm/kg of adduction and 0.16±0.19 Nm/kg of abduction (p<.001). When compared with the literature data, the forces during misstep were within the range of those forces that could result in hip fractures in the elderly. Therefore, it may be possible for the elderly to experience hip/proximal femur fractures during missteps prior to falling. 相似文献
980.
Antonio Salas José Lovo-Gómez Vanesa álvarez-Iglesias María Cerezo María Victoria Lareu Vincent Macaulay Martin B. Richards ángel Carracedo 《PloS one》2009,4(9)