Reproductive strategies in small populations: using Atlantic salmon as a case study

Abstract –  Wild salmonid populations with only a few breeding adults may not exhibit a significant reduction in genetic variability compared with larger populations. Such an observation suggests that effective population sizes are larger than population size estimates based on direct adult counts and/or the mating strategy maximises outbreeding, contributing to increased heterozygosity. In the case of wild Atlantic salmon Salmo salar populations, stratification by age classes and sexes on the spawning grounds avoids inbreeding and increases genetic variability. We studied the breeding composition of four Spanish salmon populations. Over a 7-year period we concluded that the probability of within-cohort mating is very low: females generally reproduce after two sea-winters whereas males reproduce mostly as one sea-winter ( grilse ) and/or mature parr. Considering different levels of contribution of mature parr to spawning derived from field surveys, we developed a simple model for estimating effective population sizes and found that they doubled with 65% parr contribution expected for rivers at this latitude (43°N), and ranged from 100–800 individuals. The effect of between-cohort mating was modelled considering different ranges of differences in allele frequencies between cohorts and resulted in 28–50% increases in heterozygosity when considering a 65% parr contribution. The complex mating strategy of Atlantic salmon contributes to explain the high levels of genetic variability found for small populations of this species. This model can probably be extended to other animal species with mating strategies involving different cohorts.     

浅谈我国人口与可持续发展

本文揭示了我国人口与经济环境发展及经济发展之间的矛盾，强调了控制人口的重要意义，提出了实现可持续发展的方法和途径。     

千万不可忽视良种黄牛的保种问题

阐述了良种牛保种的重要意义．基因的随机漂移、选择与杂交、近交是特定基因从群体中消失的主要原因，群体及其有效含量和系统选育的科学组织是保种的重要内容。最后介绍我国良种牛的保种方法及其存在的问题，并提出解决的办法。     

不同密度对棉花群体冠层结构及微环境的影响

以湘杂棉8号为试材．对不同种植密度处理下棉花的叶面积、群体冠层内的温度、湿度及光分布的情况进行分析。结果表明：密度处理对棉花上述几项指标均有影响，从构建良好的群体结构角度看，以30000株，hm^2最佳，39000株，hm^2次之。建议鄱阳湖棉区最佳种植密度为30000—39000株，hm^2。     

Influences of human activity and climate on the stock-recruitment dynamics of whitefish, Coregonus lavaretus, in Lake Geneva

Abstract  Analysis of long-term catches from the deep peri-alpine Lake Geneva, showed a shift in the stock-recruitment relationship of Coregonus lavaretus (L.), a target species of commercial fishing. This change was mainly related to large-scale meteorological factors. Higher spring water temperatures may have improved larval survival and hence recruitment of whitefish via: (1) a better match between the hatching date of whitefish larvae and development of their zooplankton prey; and (2) the positive temperature effect on larval growth. In Lake Geneva, changes in regulatory mechanisms coupled with stocking and improved water-quality have led to an explosion in the C. lavaretus population in recent years. These results highlight the relevance of long-term changes in the stock-recruitment relationship for management of aquatic ecosystems that are sensitive to climate forcing.     

Population Studies of Limonium stocksii (Plumbaginacea) from a Salt Desert Near the Arabian Sea Coast

Abstract

A population of Limonium stocksii was studied for one year at the upper end of Manora Creek along the Arabian Sea coast, near Karachi, Pakistan. The community was divided into three zones. Soil pH varied from 8.1 to 8.5. Soil conductivity was highest (191 dS m^?1) in September and lowest (55 dS m^?1) in June. Soil water content was relatively low and varied from 1.6% in February to 9.5% in June. Limonium stocksii maintained a persistent seed bank, which peaked at 5,887 seeds m^?2 in May. Very slow growth was observed; however, plants in the intermediate zone showed better growth than the other two zones. Stem and leaf tissue water content were affected by salinity fluctuations, but root tissue water remained unaffected. Sodium (Na⁺) and chloride (Cl^?) accumulated in stems and leaves more than other ions. Leaves also accumulated a very high amount of magnesium (Mg⁺⁺) compared to roots and stems.     

构建社会主义和谐社会与人口就业

就业是民生之本。当前，我国就业形势日趋严峻，就业问题已成为中国经济发展面临的重大挑战。文中从考察我国劳动力供求状况人手，分析我国当前的人口压力与就业形势；探讨了影响我国劳动力就业的几大因素；并提出了扩大就业的相应对策，强调政府在社会就业中负有重要责任，实现充分就业是政府宏观调控的基本目标之一。此外，充分发挥劳动者作为劳动力市场供给主体的积极作用也是非常重要的。     

濒危名贵哲罗鱼保护生物学的研究 Ⅲ.哲罗鱼的资源评价及濒危原因

哲罗鱼是我国珍稀冷水性鱼类，由于分布区域日趋缩小，种群数量急剧减少，已处于濒临灭绝的状态，其主要致危原因是生态环境改变和人为活动的干扰。     

Genetic structure of the migratory catfish Pseudoplatystoma corruscans (Siluriformes: Pimelodidae) suggests homing behaviour

Abstract –  Pseudoplatystoma corruscans is distributed widely in the La Plata Basin in Brazil, where it is a very important species because of its high commercial value and ecological role as a voracious predator. This species undertakes long migrations during the dry and rainy seasons to feed and reproduce, respectively. In this study, we analysed seven microsatellite loci to test the hypotheses of the existence of a single panmictic population of P. corruscans in the La Plata Basin. All microsatellites analysed were highly polymorphic with the number of alleles per locus ranging from seven (Pcor28) to 30 (Pcor10). Across all samples, 107 alleles were detected. Thirty alleles were private, i.e., found in only one sample. Highly significant genetic differentiation was observed among samples in three of the four analyses performed: F _ST (from 0.03435 to 0.16349, P  < 0.05), Analysis of molecular variance (amova) F _ST = 8.25% ( P  < 0.0001) and amova R _ST = 9.72% ( P  < 0.0001). A microsatellite multilocus Bayesian assignment test with the programme structure confirmed the division of the fishes into six groups largely concurrent with main branches on a population neighbour-joining tree. The obtained results rejected the panmixia hypothesis. On the other hand, the documented long-distance movements of P. corruscans and the geographical scale of genetic differentiation found in this study indicate a strong tendency for fish of this species to utilise their natal nursery regions for reproduction, which represents the first demonstrated example of homing in a freshwater catfish in South America.     

冬小麦亩产700kg土壤肥力与群体发展动态指标的研究

通过对亩产700kg超高产麦田连续多年多点跟踪调查分析研究,得出了在青岛市气象和生产条件下,实现亩产700kg超高产栽培的土壤肥力指标为有机质1.4%以上,碱解氮90mg/kg以上,速效磷35mg/kg以上,速效钾100mg/kg以上;施肥指标为有机肥3000kg/667m2,纯N 20kg/667m2,P2O510kg/667m2,K2O 10kg/667m2左右。产量构成因素指标为穗数54.2万/667m2,穗粒数35.7粒,千粒重43g;群体动态指标为基本苗13.8×104/667m2,冬前总茎数75.1×104/667m2,春季最大分蘖107.5×104/667m2左右。