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排序方式: 共有175条查询结果,搜索用时 15 毫秒
81.
82.
The amniotic fluid is a clinically accessible source of mesenchymal stem cells (AF-MSC) during gestation, which enables autologous cellular therapy for perinatal disorders. The origin of AF-MSC remains elusive: renal and neuronal progenitors have been isolated from the AF-MSC pool, yet no cells with pulmonary characteristics. We analyzed gene expression of pulmonary and renal markers of 212 clonal lines of AF-MSC isolated from amniocentesis samples. AF-MSC were cultured on dishes coated with extracellular matrix (ECM) proteins from decellularized fetal rabbit lungs. In vivo differentiation potential of AF-MSC that expressed markers suggestive of lung fate was tested by renal subcapsular injections in immunodeficient mice. Of all the isolated AF-MSC lines, 26% were positive for lung endodermal markers FOXA2 and NKX2.1 and lacked expression of renal markers (KSP). This AF-MSC subpopulation expressed other lung-specific factors, including IRX1, P63, FOXP2, LGR6, SFTC, and PDPN. Pulmonary marker expression decreased over passages when AF-MSC were cultured under conventional conditions, yet remained more stable when culturing the cells on lung ECM-coated dishes. Renal subcapsular injection of AF-MSC expressing lung-specific markers resulted in engrafted cells that were SPTB positive. These data suggest that FOXA2+/NKX2.1+/KSP- AF-MSC lines have lung characteristics which are supported by culture on lung ECM-coated dishes. 相似文献
83.
The relationship between agricultural intensification and biological control: experimental tests across Europe 总被引:2,自引:0,他引:2
Thies C Haenke S Scherber C Bengtsson J Bommarco R Clement LW Ceryngier P Dennis C Emmerson M Gagic V Hawro V Liira J Weisser WW Winqvist C Tscharntke T 《Ecological applications》2011,21(6):2187-2196
Agricultural intensification can affect biodiversity and related ecosystem services such as biological control, but large-scale experimental evidence is missing. We examined aphid pest populations in cereal fields under experimentally reduced densities of (1) ground-dwelling predators (-G), (2) vegetation-dwelling predators and parasitoids (-V), (3) a combination of (1) and (2) (-G-V), compared with open-fields (control), in contrasting landscapes with low vs. high levels of agricultural intensification (AI), and in five European regions. Aphid populations were 28%, 97%, and 199% higher in -G, -V, and -G-V treatments, respectively, compared to the open fields, indicating synergistic effects of both natural-enemy groups. Enhanced parasitoid: host and predator: prey ratios were related to reduced aphid population density and population growth. The relative importance of parasitoids and vegetation-dwelling predators greatly differed among European regions, and agricultural intensification affected biological control and aphid density only in some regions. This shows a changing role of species group identity in diverse enemy communities and a need to consider region-specific landscape management. 相似文献
84.
Hůnová I Matoušková L Srněnský R Koželková K 《Environmental monitoring and assessment》2011,183(1-4):501-515
Ozone levels in the Jizerske hory Mts. measured at 13 sites by diffusive samplers during the 2006 and 2007 vegetation seasons are presented. A significant ozone gradient (5.4 ppb in 2006 and 4.0 ppb in 2007) per 100 m difference in altitude between 370 and 1,100 m a.s.l. was recorded. High-resolution maps of phytotoxic potential were developed. The AOT40 threshold (5 ppm h) was exceeded over the entire area with the highest levels exceeding this threshold by 12 times in the upper portions of the mountains. Ozone visible injury was evaluated at four of the monitoring sites on seven native plant and tree species. Four species showed ozone-like symptoms, two of which (Rubus idaeus and Fagus sylvatica) were confirmed as ozone-induced. Our results indicate that ambient ozone is likely to have a much lower impact on the Jizerske hory Mts. vegetation than expected, considering the measured ambient ozone exposures and favourable environmental conditions for ozone uptake. 相似文献
85.
86.
Thomas B. Smith Leonard A. Freed Jaan Kaimanu Lepson John H. Carothers 《Conservation biology》1995,9(1):107-113
We report on the evolutionary change in bill size of a species of Hawaiian honeycreeper resulting from an apparent dietary shift caused by dramatic declines and extinctions of lobelioids, a historically favored nectar source. Although it now feeds mainly on the flowers of the ohia tree ( Metrosideros polymorpha ), early Hawaiian avifaunal accounts report that the i'iwi ( Vestiaria coccinea ), which has a long decurved bill, fed primarily on the flowers of Hawaiian Lobelioideae, which typically have long decurved corollas. A coevolutionary association of i'iwi bill and flower morphology has often been asserted. We test the hypothesis that the shift in the i'iwi's diet from the long corolla lobelioid flowers to ohia flowers, which lack corollas, resulted in directional selection for shorter bills. We evaluate this hypothesis by comparing the morphological characters of museum specimens from the island of Hawaii collected before 1902 with recent specimens from the Hakalau National Wildlife Refuge, Hawaii. We examine evidence of change in morphological characters using multivariate analysis and a nonparametric cubic spline technique. Results from all analyses are congruent: bill length is shorter in recent specimens. 相似文献
87.
Marcela Nováková Barbora Vašáková Hana Kutalová Katarina Galeštoková Klára Průšová Petr Šmilauer Radim Šumbera Daniel Frynta 《Behavioral ecology and sociobiology》2010,64(3):371-379
Spiny mice of the genus Acomys (Muridae) represent a very suitable mammalian model for studying factors influencing the secondary sex ratio (SSR). The maternal
effort in these rodents is extremely biased in favour of the prenatal period and, therefore, maternal manipulation of the
SSR is potentially more advantageous. We studied the SSR in four populations/species of spiny mice kept in family groups consisting
of two closely related females, one non-relative male and their descendants. The groups were established from founding animals
aged about 3 months (maturing age) and were allowed to breed freely for several months. Each litter was sexed after birth,
and relevant data were thoroughly recorded. Altogether, data were collected on 1684 litters: 189 of Acomys sp. from Iran, 203 of A. cilicicus, 875 of A. cahirinus, and 417 of A. dimidiatus. We recorded the sex of 4048 newborns of which 1995 were males and 2053 were females. The overall sex ratio was close to
1:1 (49.2%). Generalized linear mixed models and/or generalized linear models were constructed to evaluate the effect of four
life history and eight social variables on the sex ratio. No consistent effects of these variables on the sex ratio were found
and, interestingly, none of the variables associated with maternal life history had any effect on the sex ratio. Three factors
associated with group composition (i.e. the number of immature males, the number of immature females and the number of breeding
females) did have significant effects on the sex ratio, but these effects were not consistent across the studied species.
In conclusion, our evaluation of this large dataset revealed that the sex ratio in spiny mice is surprisingly stable. 相似文献
88.
Sapucci Gabriela Ribeiro Negri Rogério Galante Casaca Wallace Massi Klécia Gili 《Environmental Modeling and Assessment》2021,26(4):581-590
Environmental Modeling & Assessment - Over the past decades, the Southeast Atlantic Forest in Paraíba do Sul River Valley has suffered intense deforestation and human disturbances. Due to... 相似文献
89.
Environmental Fluid Mechanics - In this paper, an improved Shiono–Knight model (SKM) has been proposed to calculate the rectangular compound open channel flows by considering a multi-zonal... 相似文献
90.