Correlated responses to selection for large body size in oMt1a-oGH mice: growth, feed efficiency and body composition

Correlated responses were determined for growth, feed consumption, feed efficiency and body composition following short‐term selection for large 8‐week body weight in transgenic and nontransgenic mice. Replicate lines which either carried or did not carry the sheep metallothionein 1a‐sheep growth hormone transgene (oMt1a‐oGH) were established. The lines carrying the transgene at an initial frequency of 0.5 came from a high‐growth (TM) and a randomly selected (TC) background. The respective nontransgenic lines were identified as NM and NC. Control replicates (CC) came from the randomly selected background. During the selection process the transgene was activated by adding 25 mm ZnSO₄ to the drinking water of all mice. Correlated responses were measured with (Z) and without (C) the addition of zinc. After seven and eight generations of selection, the frequency of transgenic mice in line TM had fallen sharply, whereas transgene frequency had risen moderately in TC. The reduced frequency of oMt1a‐oGH in the high‐growth genetic background may have been caused by a lower additive effect compared with the randomly selected background combined with a fitness disadvantage of the transgene. Therefore, the utility of a transgene in improving a quantitative trait may depend in part on genetic background. Correlated responses for most traits in NC were similar for Z and C. In contrast, correlated responses in TC showed marked differences in C compared with Z. For example, daily gain and feed efficiency showed no significantly correlated responses under C and positive responses (p < 0.001) under Z, and the reverse was found for indicators of body fat percentage. These line by environment (Z versus C) interactions may represent a genetic correlation of less than one between a trait expressed in two distinct environments. Thus, in developing lines with a transgene that can be regulated, a critical question is whether selection for quantitative trait(s) should be conducted when the transgene is activated or not activated.     

Selected ecosystem relationships in the mercury contaminated Wabigoon-English river system,Canada, and their underlying causes

Mercury concentrations in basic ecosystem compartments of the Wabigoon-English River system are interrelated. Statistically significant correlations are evident between Hg levels in various biotic-young northern pike (Esox lucius), yearling yellow perch (Perca flavescens) and crayfish (Orconected virihs) and abiotic compartments (water, surface sediments). Highly significant positive correlations are found between methyl-mercury in water and Hg in biota. Highly significant positive correlations also exist between Hg levels in different organisms, despite differences in habitat, diet, uptake routes and proportion of bodyburden that is in the methyl form. A plausible basis for these relationships is the rapid equilibration between methyl and inorganic Hg in and between various abiotic components of the ecosystem and subsequent incorporation into food webs. As sediment-water partitioning for inorganic and methylmercury is also rapid it is likely that in lakes and slow moving river reaches, local environmental variables probably largely govern Hg body burdens in biota.     

SAP NITRATE IN FROZEN-THAWED AND REFRIGERATED STEMS OF AMARANTHUS TRICOLOR IS INDICATIVE OF NITROGEN FERTILIZER SUPPLY

Amaranthus tricolor is a potential accumulator of nitrate but nutrient sufficiency guidelines have not been developed for this vegetable. We investigated whether the shoot stem of A. tricolor is a suitable index for crop nitrate status, and whether freezing the stem, which aids sap extraction, would render it unsuitable for the analysis of nitrate and other nutrients. We grew A. tricolor at two nitrogen (N) rates (100 and 200 mg L^?1 as nitrate-N) and established that sap nitrate from both fresh and frozen-thawed stems did not differ but was significantly increased by additional N fertilizer. Shoot growth was correspondingly higher with additional N. Therefore, the stem is a suitable index for crop nitrate. Boron (B), calcium (Ca), iron (Fe), magnesium (Mg), manganese (Mn), molybdenum (Mo), sodium (Na) and sulfur (S) were significantly affected by frozen storage but potassium (K), phosphorus (P) and zinc (Zn) were not. A single sufficiency guideline is possible for these nutrients, for use with both fresh and frozen-thawed stem sap.     

北京山区天然侧柏林种内竞争研究

该文采用逐步扩大范围的方法确定影响对象木的最佳竞争范围,利用Hegyi单木竞争指数对锥峰山林场天然侧柏种内竞争强度进行了定量分析,并与典型人工侧柏林种内竞争强度进行对比分析。结果表明:在天然侧柏群落中对象木的最佳竞争距离为5m;天然侧柏的种内竞争强度随着林木径级的增大而减小;竞争指数与对象木胸径服从幂函数关系,从模型预测结果可知当侧柏胸径达20cm以上时,竞争强度变化很小;与天然侧柏林相比,人工侧柏林的种内竞争强度较小,群落年龄结构不够合理。     

Estimating the mass of asteroid 253 mathilde from tracking data during the NEAR flyby

The terminal navigation of the Near Earth Asteroid Rendezvous (NEAR) spacecraft during its close flyby of asteroid 253 Mathilde involved coordinated efforts to determine the heliocentric orbits of the spacecraft and Mathilde and then to determine the relative trajectory of the spacecraft with respect to Mathilde. The gravitational perturbation of Mathilde on the passing spacecraft was apparent in the spacecraft tracking data. As a result of the accurate targeting achieved, these data could be used to determine Mathilde's mass as 1.033 (+/- 0.044) x 10(20) grams. Coupled with a volume estimate provided by the NEAR imaging team, this mass suggests a low bulk density for Mathilde of 1.3 grams per cubic centimeter.     

A "Schrodinger Cat" Superposition State of an Atom

A "Schrodinger cat"-like state of matter was generated at the single atom level. A trapped 9Be+ ion was laser-cooled to the zero-point energy and then prepared in a superposition of spatially separated coherent harmonic oscillator states. This state was created by application of a sequence of laser pulses, which entangles internal (electronic) and external (motional) states of the ion. The Schrodinger cat superposition was verified by detection of the quantum mechanical interference between the localized wave packets. This mesoscopic system may provide insight into the fuzzy boundary between the classical and quantum worlds by allowing controlled studies of quantum measurement and quantum decoherence.     

北京密云水库集水区刺槐种群生活史特征

该文以种群生命表及生存分析理论为基础,在对密云地区进行调查的基础上,编制刺槐种群静态生命表,绘制了刺槐的存活曲线、死亡率曲线、亏损率曲线、死亡密度函数曲线、积累死亡函数曲线和危险率函数曲线,分析种群生命过程,研究了北京密云地区刺槐人工林刺槐种群动态和数量特征。结果表明,刺槐存活曲线趋于Deevey--Ⅰ型,并应用谱分析方法研究了刺槐种群动态,在刺槐种群更新过程中存在着明显的周期性;刺槐种群在群落中占优势地位。