Dispersal of introduced house sparrows Passer domesticus: an experiment

An important issue concerning the introduction of non-indigenous organisms into local populations is the potential of the introduced individuals to spread and interfere both demographically and genetically with the local population. Accordingly, the potential of spatial dispersal among introduced individuals compared with local individuals is a key parameter to understand the spatial and temporal dynamics of populations after an introduction event. In addition, if the variance in dispersal rate and distance is linked to individual characteristics, this may further affect the population dynamics. We conducted a large-scale experiment where we introduced 123 house sparrows from a distant population into 18 local populations without changing population density or sex ratio. Introduced individuals dispersed more frequently and over longer distances than residents. Furthermore, females had higher probability of dispersal than males. In females, there was also a positive relationship between the wing length and the probability of dispersal and dispersal distance. These results suggest that the distribution and frequency of introduced individuals may be predicted by their sex ratio as well as their phenotypic characteristics.     

Seasonal cycles of species diversity and similarity in a tropical butterfly community

1. Studies of seasonality in ecological diversity rarely extend over more than a few years, and few studies of seasonal diversity have explicitly investigated the influence of environmental factors on seasonal community composition, especially in tropical communities. 2. Our 10 years of monthly sampling in Amazonian Ecuador yielded 20 996 individuals of 137 fruit-feeding butterfly species. Seasonal cycles of rainfall drive annual cycles in species diversity and community similarity. Undetermined processes operating most strongly during the dry season maintain species diversity and high community similarity across years. 3. Seasonal cycles in community diversity and similarity are superimposed on a gradual decline in similarity between community samples on a decadal time-scale because of long-term changes in species abundances. 4. Monitoring and analysis of changes in community composition over a range of time-scales can be used to refine models of community dynamics by incorporating environmental factors necessary to predict the ecological impact of future climate change.     

KLRE/I1 and KLRE/I2: a novel pair of heterodimeric receptors that inversely regulate NK cell cytotoxicity

NK cells identify infected, neoplastic, or MHC-disparate target cells via several different receptors. The NK cell receptor KLRE1 lacks known signaling motifs but has nevertheless been shown to regulate NK cell-mediated cytotoxicity. Here we demonstrate that KLRE1 forms functional heterodimers with either KLRI1 or KLRI2. Cotransfection with KLRE1 was necessary for surface expression of the NK cell receptor chains KLRI1 and KLRI2 in 293T cells. Moreover, KLRE1 can be coimmunoprecipitated with KLRI1 or KLRI2 from transfected NK cell lines. By flow cytometry, KLRE1 and KLRI1 showed colinear expression on NK cells, suggesting surface expression as heterodimers. Unlike other killer cell lectin-like receptors, KLRE1/KLRI1 and KLRE1/KLRI2 heterodimers predominantly migrated as single chains in SDS-PAGE, indicating noncovalent association. KLRI1 was coimmunoprecipitated with the tyrosine phosphatase Src homology region 2 domain-containing phosphatase 1. In accordance with an inhibitory function, anti-HA Ab induced reduced killing of FcR-bearing targets by KLRI1-HA-transfected NK cell lines in a redirected cytotoxicity assay. Reciprocally, KLRI2-HA transfectants displayed increased killing in this assay. Finally, Ab to KLRE1 induced inhibition in KLRI1-transfected cells but increased cytotoxicity in KLRI2 transfectants, demonstrating that KLRE/I1 is a functional inhibitory heterodimer in NK cells, whereas KLRE/I2 is an activating heterodimeric receptor.     

The spatial scale of population fluctuations and quasi-extinction risk

Using a spatially homogeneous population model with migration (random individual dispersal) and spatially autocorrelated environmental noise, we show how migration and local density regulation affect the spatial scale of fluctuations in the log of population sizes as well as the 1-yr differences in these. The difference between the squares of these two spatial scales of population fluctuations does not depend on the spatial scale of the noise but only on migration rate and strength of local density regulation. We also show how migration, local density regulation, and spatially correlated environmental noise affect the realized population process at a specific location. As the migration increases, the realized local density regulation and the expected population size increase, while the realized environmental noise decreases. This approach also enables us to analyze the dynamics of the total population size within quadrats of different sizes. The risk of local quasi extinction is strongly reduced by increasing quadrat size or migration rate, while an increase in environmental stochasticity or spatial correlation in the environmental noise increases the risk of quasi extinction.     

Predicting the time to quasi-extinction for populations far below their carrying capacity

Populations threatened by extinction are often far below their carrying capacity. A population collapse or quasi-extinction is defined to occur when the population size reaches some given lower density. If this density is chosen to be large enough for the demographic stochasticity to be ignored compared to environmental stochasticity, then the logarithm of the population size may be modelled by a Brownian motion until quasi-extinction occurs. The normal-gamma mixture of inverse Gaussian distributions can then be applied to define prediction intervals for the time to quasi-extinction in such processes. A similar mixture is used to predict the population size at a finite time for the same process provided that quasi-extinction has not occurred before that time. Stochastic simulations indicate that the coverage of the prediction interval is very close to the probability calculated theoretically. As an illustration, the method is applied to predict the time to extinction of a declining population of white stork in southwestern Germany.     

Cultivation of HL-60 cells in a serum-free medium containing granulocyte/macrophage colony-stimulating factor.

In order to develop a defined cultivation medium for HL-60 cells, we cultivated these cells in a serum-free suspension medium and tested the effect of various growth factors. Of the factors tested, granulocyte/macrophage colony-stimulating factor was most active in growth stimulation. A much lower effect was obtained with granulocyte colony-stimulating factor and transferrin. No effect was found with interleukin-3 and insulin. Granulocyte colony-stimulating factor was the only growth factor tested that also induced differentiation as judged by the nitroblue tetrazolium test. Growth of HL-60 cells in medium containing granulocyte/macrophage colony-stimulating factor (125 U/ml) and transferrin (5 micrograms/ml) as the only protein factors was similar to growth in medium containing 10% serum. No increase in spontaneous differentiation of HL-60 cells in this defined medium was observed. Physiological concentrations of retinol bound to retinol-binding protein and retinyl ester in chylomicron remnants reduced proliferation as well as the level of c-myc oncoprotein and induced differentiation of HL-60 cells cultivated in defined medium. Hence, this defined medium may be useful when studying the function of retinoids in HL-60 cells.     

1,25-dihydroxyvitamin D-3 and 24,25-dihydroxyvitamin D-3 affect parathormone (PTH) -sensitive adenylate cyclase activity and alkaline phosphatase secretion of osteoblastic cells through different mechanisms of action

In UMR 106 rat osteosarcoma cells, parathormone (1-34hPTH) and calcitonin (sCT) stimulated adenylate cyclase (AC) activity 5.5-and 2.8-fold, respectively. AC in osteoblasts (OB) from collagenase-treated calvaria of 3-day-old rats responded similarly to 1-34hPTH. In contrast, fibroblasts (mouse fibroblastomas) displayed a marginal 1-34hPTH sensitive AC. Osteoclasts (OC) of collagenase-treated rat calvariae, rat monocytes and mouse macrophages did not demonstrate 1-34hPTH inducable AC activity. Physiological concentrations of 24,25-dihydroxyvitamin D-3 attenuated PTH-sensitive AC in OB and UMR 106 cells within 20 min, while 1,25-dihydroxyvitamin D-3 showed no such immediate effect. In contrast, the AC response to Gpp(NH)p was unaffected by 24,25-(OH)2D3, indicating that 24,25-(OH)2D3 interrupts the coupling of the PTH receptor to the GTP binding protein Gs. OB and UMR 106 cells were also subjected to long-term (48 h) incubation with vitamin D-3 metabolites, 1-34hPTH or 20% serum from patients with secondary hyperparathyroidism (sHBT-serum), respectively. PTH-sensitive AC was markedly attenuated by pre-exposure to both 1-34hPTH and 1,25-(OH)2D3, while minimally affected by corresponding 24,25-(OH)2D3 and 20% sHPT-serum treatment. The secretion of alkaline phosphatase (Alphos) from the two cell types was strongly increased by 1-34hPTH, the effect being abolished by the presence of 24,25-(OH)2D3. Iliac crest biopsies of normal individuals exhibited a clear negative correlation between PTH-sensitive AC and corresponding serum 24,25-(OH)2D3 levels. Basal AC activity was, however, negatively correlated to serum 1,25-(OH)2D3 concentrations. In summary, the results show that 24,25-(OH)2D3 reduces PTH-stimulated AC activity in and Alphos secretion from osteoblastic bone cells by rapidly and directly interfering with the plasma membrane. These data reinforce the probable in vivo significance of 24,25-(OH)2D3. Moreover, the negative correlation between basal AC activity and serum 1,25-(OH)2D3 levels indicates a possible role for 1,25-(OH)2D3 in regulating bone cell synthesis of AC components in vivo.     

Proliferation failure and gamma radiation sensitivity of Fen1 null mutant mice at the blastocyst stage

Flap endonuclease 1 (FEN1) has been shown to remove 5' overhanging flap intermediates during base excision repair and to process the 5' ends of Okazaki fragments during lagging-strand DNA replication in vitro. To assess the in vivo role of the mammalian enzyme in repair and replication, we used a gene-targeting approach to generate mice lacking a functional Fen1 gene. Heterozygote animals appear normal, whereas complete depletion of FEN1 causes early embryonic lethality. Fen1(-/-) blastocysts fail to form inner cell mass during cellular outgrowth, and a complete inactivation of DNA synthesis in giant cells of blastocyst outgrowth was observed. Exposure of Fen1(-/-) blastocysts to gamma radiation caused extensive apoptosis, implying an essential role for FEN1 in the repair of radiation-induced DNA damage in vivo. Our data thus provide in vivo evidence for an essential function of FEN1 in DNA repair, as well as in DNA replication.     

Cytotoxicity and cytokinetic effects of mitomycin C and/or photochemotherapy in a human colon adenocarcinoma cell line.

1. The cytotoxicity and cytokinetic effects of Mitomycin C (MC) and/or photochemotherapy (PCT) in cultured human colon adenocarcinoma (WiDr) cells were investigated using colony formation to determine cell survival and DNA flow cytometry to analyze cell kinetics. 2. A low concentration of MC (0.01 micrograms/ml) caused accumulation of cells in late S and early G2 phase; higher concentrations (0.05-0.5 micrograms/ml) induced accumulation of the cells in mid and early S phase. 3. The effects of the lowest concentration of MC (0.01 micrograms/ml) were reversible upon removal of the drug, whereas a higher concentration of MC (0.1 micrograms/ml) resulted in a permanent inhibition of cell cycle progression. 4. The sensitivity of Photofrin II-loaded cells to PCT can be enhanced significantly by the addition of MC. 5. The MC-induced accumulation of the cells in S phase may be one reason for the increased cytotoxicity of PCT combined with MC. 6. The data suggest that MC may also inhibit repair of PCT-induced DNA damage.