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21.
22.
Food availability is important to the dynamics of animal social organizations or populations. However, the role of winter
food availability in animal population dynamics is still controversial. We carried out an experimental study to test Lack’s
hypothesis that reduced food in winter limits survival and spring numbers of breeding individuals of social groups, using
the Mongolian gerbil (Meriones unguiculatus) as model species. We established 24 gerbil social groups in 24, 10 × 10 m, pens in September 2008. We provided wheat seeds
as supplemental food in 12 enclosures from September 2008 to March 2009; the other 12 enclosures, not provided with supplemental
food, served as controls. We live-trapped gerbils at a 2-week interval from September to April. Supplemental food during winter
increased biweekly survival by 10% relative to that in control groups. Only four control social groups survived to the end
of our study whereas all 12 food-supplemented social groups survived through our study period. Supplemental food also increased
cumulative numbers of recruits and group sizes of gerbils. We conclude that winter food availability limits winter survival
and spring social groups or population sizes of Mongolian gerbils. 相似文献
23.
Sergio Cardoso Laura Valverde Miguel A. Alfonso-Sánchez Leire Palencia-Madrid Xabier Elcoroaristizabal Jaime Algorta Susana Catarino David Arteta Rene J. Herrera María Teresa Zarrabeitia José A. Pe?a Marian M. de Pancorbo 《PloS one》2013,8(7)
The European genetic landscape has been shaped by several human migrations occurred since Paleolithic times. The accumulation of archaeological records and the concordance of different lines of genetic evidence during the last two decades have triggered an interesting debate concerning the role of ancient settlers from the Franco-Cantabrian region in the postglacial resettlement of Europe. Among the Franco-Cantabrian populations, Basques are regarded as one of the oldest and more intriguing human groups of Europe. Recent data on complete mitochondrial DNA genomes focused on macrohaplogroup R0 revealed that Basques harbor some autochthonous lineages, suggesting a genetic continuity since pre-Neolithic times. However, excluding haplogroup H, the most representative lineage of macrohaplogroup R0, the majority of maternal lineages of this area remains virtually unexplored, so that further refinement of the mtDNA phylogeny based on analyses at the highest level of resolution is crucial for a better understanding of the European prehistory. We thus explored the maternal ancestry of 548 autochthonous individuals from various Franco-Cantabrian populations and sequenced 76 mitogenomes of the most representative lineages. Interestingly, we identified three mtDNA haplogroups, U5b1f, J1c5c1 and V22, that proved to be representative of Franco-Cantabria, notably of the Basque population. The seclusion and diversity of these female genetic lineages support a local origin in the Franco-Cantabrian area during the Mesolithic of southwestern Europe, ∼10,000 years before present (YBP), with signals of expansions at ∼3,500 YBP. These findings provide robust evidence of a partial genetic continuity between contemporary autochthonous populations from the Franco-Cantabrian region, specifically the Basques, and Paleolithic/Mesolithic hunter-gatherer groups. Furthermore, our results raise the current proportion (≈15%) of the Franco-Cantabrian maternal gene pool with a putative pre-Neolithic origin to ≈35%, further supporting the notion of a predominant Paleolithic genetic substrate in extant European populations. 相似文献
24.
The direct binding of porcine pancreatic phospholipase A2 and its zymogen to 1,2-bis(heptanylcarbamoyl)-rac-glycerol 3-sulfate was studied by optical detection of triplet-state magnetic resonance spectroscopy in zero applied magnetic field. The zero-field splittings of the single Trp3 residue undergo significant changes upon binding of phospholipase A2 to lipid. Shifts in zero-field splittings, characterized mainly by a reduction of the E parameter from 1.215 to 1.144 GHz, point to large changes in the Trp3 local environment which accompany the complexing of phospholipase A2 with lipid. This may be attributed to Stark effects caused by the binding of a charged group near Trp3 in the enzyme-lipid complex. The cofactor, Ca2+, which is strongly bound to the enzyme active site, has an influence on the bonding, as reflected by smaller zero-field splitting shifts. A relatively small change in the Trp environment was observed for the interaction of the zymogen with lipid. 相似文献
25.
Carbon and nitrogen stable isotope analyses have improved our understanding of food webs and movement patterns of aquatic
organisms. These techniques have recently been applied to diet studies of elasmobranch fishes, but isotope turnover rates
and isotope diet–tissue discrimination are still poorly understood for this group. We performed a diet switch experiment on
captive sandbar sharks (Carcharhinus plumbeus) as a model shark species to determine tissue turnover rates for liver, whole blood, and white muscle. In a second experiment,
we subjected captive coastal skates (Leucoraja spp.) to serial salinity reductions to measure possible impacts of tissue urea content on nitrogen stable isotope values.
We extracted urea from spiny dogfish (Squalus acanthias) white muscle to test for effects on nitrogen stable isotopes. Isotope turnover was slow for shark tissues and similar to
previously published estimates for stingrays and teleost fishes with low growth rates. Muscle isotope data would likely fail
to capture seasonal migrations or diet switches in sharks, while liver and whole blood would more closely reflect shorter
term movement or shifts in diet. Nitrogen stable isotope values of skate blood and skate and dogfish white muscle were not
affected by tissue urea content, suggesting that available diet–tissue discrimination estimates for teleost fishes with similar
physiologies would provide accurate estimates for elasmobranchs. 相似文献
26.
IN addition to its well known antiviral activity, interferon has recently been shown to inhibit the multiplication of tumour and mammalian cells in cell culture1–6. We report here the inhibition by interferon of DNA synthesis induced in mouse spleen lymphocytes by the non-viral stimuli phytohaemagglutinin (PHA) and allogeneic lymphocytes. These findings are in accord with our contention that interferon affects cell function and, furthermore, they suggest that by acting on lymphocytes, interferon plays a role in the immunological response of the host. 相似文献
27.
28.
29.
GD25 cells lacking the beta1 integrin subunit or expressing beta1A with certain cytoplasmic mutations have poor directed cell migration to platelet-derived growth factor (PDGF) or epidermal growth factor (EGF), ligands of receptor tyrosine kinases, or to lysophosphatidic acid (LPA), a ligand of G-protein-coupled receptors (Sakai, T., Zhang, Q., F?ssler, R., and Mosher, D. F. (1998) J. Cell Biol. 141, 527-538 and Sakai, T., Peyruchaud, O., F?ssler, R., and Mosher, D. F. (1998) J. Biol. Chem. 273, 19378-19382). We demonstrate here that LPA synergizes with signals induced by beta1A integrins and ligated EGF or PDGF receptors to modulate migration. When LPA was mixed with EGF or PDGF, migration was greater than with EGF or PDGF alone. The enhancement was greater for beta1A-expressing cells than for beta1-null cells. Cells expressing beta1A with mutations of prolines or tyrosines in conserved cytoplasmic NPXY motifs had blunted migratory responses to mixtures of LPA and EGF or PDGF. The major effects on beta1A-expressing cells of LPA when combined with EGF or PDGF were to sensitize cells so that maximal responses were obtained with >10-fold lower concentrations of growth factor and increase the chemokinetic component of migration. Sensitization by LPA was lost when cells were preincubated with pertussis toxin or C3 exotransferase. There was no evidence for transactivation or sensitization of receptors for EGF or PDGF by LPA. EGF or PDGF and LPA caused activation of mitogen-activated protein kinase by pertussis toxin-insensitive and -sensitive pathways respectively, but activation was not additive. These findings indicate that signaling pathways initiated by the cytoplasmic domains of ligated beta1A integrins and tyrosine kinase receptors interact with signaling pathways initiated by LPA to facilitate directed cell migration. 相似文献
30.