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1.
Alain Danet;Susana Bautista;Alexandre Génin;Andrew P. Beckerman;Fabien Anthelme;Sonia Kéfi; 《Oikos》2024,2024(9):e10303
Climate change is expected to lead to a drier world, with more frequent and severe droughts, constituting a growing threat to biodiversity, especially in drylands. Positive plant−plant interactions, such as nurse plants facilitating beneficiary communities in their understorey, could mitigate such climate-induced stress. However, testing the real-world relevance of nurse facilitation under drought requires accounting for interactions within the diverse beneficiary communities, which may reduce, or amplify the buffering effect of a nurse. Here, we investigated when and how the interactions among nurse plants and beneficiary community members buffered drought effects in a Mediterranean semiarid abandoned cropland. We transplanted sapling beneficiary communities of either one or three species either under a nurse or in open microsites for different soil moisture levels through watering. Net facilitative effects on survival and biomass were only observed when beneficiary communities were species-diverse and under drought (without watering), meaning that under these conditions, facilitation provided by the nurse had larger positive effects than the negative effects stemming from competition with the nurse and among beneficiary species. Nurses appear to be generating these increases in survival and biomass in drought conditions via two mechanisms commonly associated with watering in open sites: they generate complementarity among the beneficiaries and shift traits to lower stress profiles. Contrasting with watering, which was found to enhance competitive hierarchy, our study shows that nurses appear to alter species dominance, favouring the less competitive species. Our results highlight three mechanisms (complementarity, competitive dominance, and trait plasticity) by which nurse species could mitigate the loss of biodiversity and biomass production due to water stress. Maintaining and supporting nurse species is thus a potentially pivotal approach in the face of projected increase in drought conditions for many drylands across the world. 相似文献
2.
K P Beckerman R D Schreiber P Needleman 《Prostaglandins, leukotrienes, and essential fatty acids》1992,47(3):231-238
Intraperitoneal infection with Listeria monocytogenes (LM) results in activation of the peritoneal macrophage population which displays increased surface expression of major histocompatibility (MHC) Class II (Ia) antigen and markedly suppressed prostaglandin (PG) synthesis. We demonstrate here that this decrease in PG production is also seen after treatment by mitogen (Con A) and endotoxin (LPS), and can be explained by reduced cyclooxygenase activity in these cell populations. We show that, whereas Ia expression was augmented at all doses of LM and Con A tested, it displayed a biphasic response to LPS in vivo: increase at the lowest dose and inhibition at higher doses. In order to identify possible endogenous mediators of these responses, we used highly purified preparations of recombinant murine (rMu) cytokines and neutralizing cytokine specific monoclonal antibodies (MAbs) to examine whether interferon-gamma (IFN-gamma) and/or tumor necrosis factor (TNF) down-regulate macrophage cyclooxygenase activity in vivo. We found that IFN-gamma induced Ia expression but had no effect on PG secretion. In contrast, TNF-alpha suppressed PG synthesis and inhibited Ia surface expression. Similarly, in our model of Con A-induced peritoneal macrophage activation, pretreatment of animals with a neutralizing MAb to rMuIFN-gamma completely blocked the induction of Ia positive macrophages by Con A but did not affect Con A-dependent suppression of PG synthesis. Pretreatment with MAb to TNF had no effect on Con A-induced Ia levels, but significantly inhibited suppressed PG synthesis.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
3.
Abundant representation of sharks in the fossil record makes this group asuperb system in which to investigate rates and patterns of molecularevolution and to explore the strengths and weaknesses of phylogeneticinferences from molecular data. In this report, the molecular evolution ofthe cytochrome b gene in sharks is described and the information related toresults from phylogenetic analysis of the data evaluated in the light of aphylogeny derived independently of the molecular data. Across divergentlineages of sharks there is evidence for significant substitution ratevariation, departure from compositional equilibrium, and substantialhomoplasy; nevertheless, the signal of evolutionary history is evident inpatterns of shared transversions and amino acid replacements. 相似文献
4.
Barbara Beckerman Glide G. Gray Eaton Deanne F. Johnson Julie Worlein 《International journal of primatology》1986,7(2):139-155
The behavioral interactions of 22 infant and mother Japanese macaques with other group members were studied. Focal-animal observations were made from the time of each infant’s birth until 1 year of age. Infants and mothers both displayed exceedingly strong preferences for associating with matrilineal kin and, specifically, for female kin. The degree of genetic relatedness was positively correlated with levels of spatial proximity, contact, grooming, aggression, and play. Overall frequencies of interactions with nonkin were very low, and partner sex was not an important factor in interactions with nonkin. There were no significant differences between male and female infants in interactions with kin versus nonkin. There was only one significant difference between male and female infants in interactions with males versus females: female infants showed stronger preferences for initiating proximity with females over males than did male infants. Because mothers provide the focal point for infant interactions during the first year of life, we compared the behavior of infants and mothers. Mothers were the recipients of more social interactions than were infants, mothers engaged in more grooming than did infants, and infants engaged in more social play than did mothers. These findings are only partially consistent with kin-selection theory, and the inadequacies of studying matrilineal kin discrimination to test kin selection are reviewed. The near-absence of infant sex differences in associations with social partners suggests that although maternal kin other than the mother are important to infant socialization, they probably do not contribute to the development of behavioral sex differences until after the first year of life. 相似文献
5.
The supply of energy, and the frequency of disturbance can both affect species diversity, often, although not always, producing unimodal diversity patterns along an energy or disturbance gradient. However, it has been suggested that diversity is a combined function of both factors, and the dynamic equilibrium model proposed by Huston (1979) is one formalization of this suggestion. This idea has received little direct testing. Here we carry out such a test using protist microcosms, in a factorial manipulation of six levels of energy (quantity of organic resource) and five levels of disturbance (frequency of temperature shock). Species richness responded to both energy supply and disturbance frequency, although not always unimodally. Patterns of response changed over time, and there was some evidence of an interaction between energy and disturbance at two of six time intervals. However, the specific form of this interaction differs from that predicted by the dynamic equilibrium model, and overall, the results provide little support for the model. 相似文献
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8.
There is marked heterogeneity of nucleotide composition in mitochondrialDNA across divergent animals. Differences in nucleotide compositionpresumably reflect differences in directional nucleotide substitution forA+T or G+C nucleotides. In mitochondrial DNA, there is A+T directionalnucleotide substitution in most (if not all) animals surveyed, and themagnitude of directional A+T nucleotide substitution differs greatly withinand among groups. Differences in directional nucleotide substitution amonglineages of mammals can be explained by changes in metabolic physiology.This relationship is thought to be mediated by the effect of oxygenradicals because these toxic compounds are by-products of aerobicmetabolism and are known mutagens. Association between metabolism andnucleotide composition provides additional evidence in favor of thehypothesis that rates and patterns of nucleotide substitution inmitochondrial DNA can be influenced by factors that impinge on rates ofendogenous DNA damage. 相似文献
9.
A method of rapid freezing in supercooled Freon 22 (monochlorodifluoromethane) followed by cryoultramicrotomy is described and shown to yield ultrathin sections in which both the cellular ultrastructure and the distribution of diffusible ions across the cell membrane are preserved and intracellular compartmentalization of diffusabler ions can be quantitated. Quantitative electron probe analysis (Shuman, H., A.V. Somlyo, and A.P. Somlyo. 1976. Ultramicros. 1:317-339.) of freeze-dried ultrathin cryto sections was found to provide a valid measure of the composition of cells and cellular organelles and was used to determine the ionic composition of the in situ terminal cisternae of the sarcoplasmic reticulum (SR), the distribution of CI in skeletal muscle, and the effects of hypertonic solutions on the subcellular composition if striated muscle. There was no evidence of sequestered CI in the terminal cisternae of resting muscles, although calcium (66mmol/kg dry wt +/- 4.6 SE) was detected. The values of [C1](i) determined with small (50-100 nm) diameter probes over cytoplasm excluding organelles over nuclei or terminal cisternae were not significantly different. Mitochondria partially excluded C1, with a cytoplasmic/ mitochondrial Ci ratio of 2.4 +/- 0.88 SD. The elemental concentrations (mmol/kg dry wt +/- SD) of muscle fibers measured with 0.5-9-μm diameter electron probes in normal frog striated muscle were: P, 302 +/- 4.3; S, 189 +/- 2.9;C1, 24 +/- 1.1;K, 404 +/- 4.3, and Mg, 39 +/- 2.1. It is concluded that: (a) in normal muscle the \"excess CI\" measured with previous bulk chemical analyses and flux studies is not compartmentalized in the SR or in other cellular organelles, and (b) the cytoplasmic C1 in low [K](0) solutions exceeds that predicted by a passive electrochemical distribution. Hypertonic 2.2 X NaCl, 2.5 X sucrose, or 2.2 X Na isethionate produced: (a) swollen vacuoles, frequently paired, adjacent to the Z lines and containing significantly higher than cytoplasmic concentrations of Na and Cl or S (isethionate), but no detectable Ca, and (b) granules of Ca, Mg, and P = approximately (6 Ca + 1 Mg)/6P in the longitudinal SR. It is concluded that hypertonicity produces compartmentalized domains of extracellular solutes within the muscle fibers and translocates Ca into the longitudinal tubules. 相似文献
10.
CD7 is a differentiation marker that identifies multiple CD8 T cell effector subsets 总被引：4，自引：0，他引：4
Aandahl EM Sandberg JK Beckerman KP Taskén K Moretto WJ Nixon DF 《Journal of immunology (Baltimore, Md. : 1950)》2003,170(5):2349-2355
The adaptive immune response of human CD8 T cells to invading pathogens involves the differentiation of naive cells into memory and effector cells. However, the lineage relationship between memory and effector cells and the differentiation of CD8 T cells into distinct subsets of effector cell subpopulations are subjects of considerable debate. CD7 identifies three populations of CD8 T cells: CD7 high (CD7(high)), low (CD7(low)), and negative (CD7(neg)) that translate into subsets with distinct functional properties. The CD7(high) subset contains naive and memory cells and the CD7(low) and CD7(neg) subsets contain effector cells. The effector cells can functionally be divided into cytokine-secreting effector CD8 T cells and lytic effector CD8 T cells. These data provide a model of human CD8 T cell differentiation in which specialized distinct subpopulations can be identified by expression of CD7. 相似文献