Genetics of neotropical fish: from chromosomes to populations

The Neotropical freshwater fish fauna is very rich—according to the most recent catalogue 71 families and 4,475 species have been described. However, only a small amount of general information is available on the composition of Neotropical marine fishes. In Brazil, 1,298 marine species have been recorded. General analysis of available cytogenetic and population genetic data clearly indicates research has been mainly concentrated on freshwater fishes. Thus, today, cytogenetic information is available for 475 species of Characiformes, 318 species of Siluriformes, 48 species of Gymnotiformes, 199 freshwater species that do not belong to the superorder Ostariophysi, and only 109 species of marine fishes. For the species studied, only about 6% have sex chromosomes and about 5% have supernumerary or B chromosomes. A review of the cytogenetic studies shows that these data have provided valuable information about the relationships between fish groups, the occurrence of cryptic species and species complexes, the mechanism of sex determination and sex chromosome evolution, the distribution of nucleolus organizer regions, the existence supernumerary chromosomes, and the relationship between polyploidy and evolution. In relation to populations in Neotropical marine waters, the studies have shown the presence of cryptic species, which has important implications for fishery management. Different levels of genetic structuring can be found among Neotropical freshwater migratory fish species. This raises important implications for fish population genetic diversity and consequently its sustainable utilization in inland fisheries and aquaculture, specifically for conservation of ichthyo-diversity and survival.     

CIMMYT和我国玉米种质群体的配合力及杂种优势分析

采用NCⅡ遗传交配设计,以丹340、Mo17、掖478和黄早四为测验种,通过2年1点田间试验,分析27个国内外玉米群体（14个CIMMYT热带、亚热带群体和13个国内群体）的主要性状配合力和产量杂种优势,并划分杂种优势群。结果表明,大多数CIMMYT群体的产量和产量性状配合力及杂种优势明显优于国内玉米群体,以Suwan l、Pob43、Pob21     

岷江百合生境及遗传多样性

在踏查岷江百合分布区的基础上随机选取两个阴坡与阳坡群体,设样地调查其群落特征,测定其土壤化学性质指标,并用ISSR分子标记分析两群体遗传多样性。结果表明,岷江百合生长在兰花莸、小角柱花、美丽胡枝子、黄花蒿等为优势的干旱河谷灌丛中,在垂直结构上居于灌木层片。数量上较多,但因冠副较小,群落外貌上不明显。土壤为褐土,呈弱碱性,土壤潜在肥力水平较高,但有效成分较低。阴坡土壤有效成分高于阳坡。物种水平的多态性谱带的比例为96.72%,有效等位基因数为1.5572,Shannon’s多样性指数为0.4932,平均期望杂合度为0.3276。其中阴坡群体的遗传多样性参数要高于阳坡群体。群体间遗传差异占总遗传差异的17.57%,群体内遗传差异占总遗传差异的82.43%。两个群体间的基因流为5.0660,说明两群体亲缘关系较近,而群体内遗传分化强烈,阴坡群体的遗传分化强于阳坡群体。     

白羊草灌丛草地种群生态位的研究

运用以Shannon-Wieren指数为基础的生态位宽度计测公式和Pianka的生态位重叠计测公式,在土壤水分、土壤pH值、土壤全氮含量3个资源维上研究白羊草灌丛草地主要植物种群生态位宽度和生态位重叠关系。建群种白羊草的平均生态位最高,为0．905;达乌里胡枝子的生态位宽度仅次于白羊草。表明白羊草、达乌里胡枝子具有最强的耐受北方寒冷干燥及家畜放牧利用的能力。白羊草在3个资源维上同其他种群的生态住重叠值都较高,表明其在群落中具有较强的占据资源优势能力。因此,在对退化白羊草灌丛草地植被恢复时,白羊草和达乌里胡枝子是首选草种。     

Do riparian buffer strips mitigate the impacts of clearcutting on small mammals?

We assessed the impact of clearcutting on small mammals in riparian areas and evaluated riparian buffer strips as a tool for conserving small mammals in managed forests. Over two summers, we trapped small mammals of seven species in riparian areas in southwestern British Columbia, Canada. Communities of small mammals were compared across three different habitat types: (1) clearcut to the stream bank, (2) clearcut with a 30 m riparian buffer strip, and (3) control (no logging). Species richness was significantly lower in clearcuts than in controls and buffers. On clearcut sites, creeping voles were more abundant, but red-backed voles and dusky shrews were less abundant than at the control sites. At sites with riparian buffer strips, both voles were present in numbers similar to those found in controls, but dusky shrews were less common. Significantly more deer mice and creeping voles were infested with bot flies at clearcut sites than at buffer sites, and no animals were infested at any of the control sites. Riparian reserves appear to be useful in reducing the short-term impacts of clearcutting on small mammal communities, though they do not eliminate these impacts altogether.     

玉米高产与群体整齐度间关系的调查分析

无效株是影响群体整齐度的重要因素,主要包括：自交株、空秆、小穗株及病虫害株等。不同产量水平的玉米群体中无效株率不同,无效株率越低,产量越高。在高密度条件下高的单株产量乃是高产的重要前提。提高种子和耕种质量,留大、壮苗是降低群体无效株,提高群体及果穗整齐度的重要措施,是进一步挖掘群体增产潜力的重要保证。     

DNA and morphological diversity of selected Greek tomato (Solanum lycopersicum L.) landraces

Utilizing inter-simple sequence repeats (ISSRs), the genetic diversity of 33 Greek tomato (Solanum lycopersicum L.) landraces and three cultivars, three cherry tomato (S. lycopersicum var.cerasiforme) cultivars and two accessions of Solanum pimpinellifolium L. was studied. Furthermore, 12 ISSR primers were also used to identify 27 morphotypes derived from 7 landraces. Based on Jaccard's coefficient, an average genetic similarity of 0.797 (ranged from 0.56 to 0.95) was found among the accessions. Cluster analysis using the UPGMA method placed all tomato landraces and cultivars into a single group, while the cherry hybrids and the S. pimpinellifolium accessions were placed in a second group. The ISSR data distinguished all the 27 morphotypes from each other and grouped the morphotypes derived from the same landrace together. The ISSR technology proved useful in describing genetic diversity among Greek tomato landraces and was capable of distinguishing the closely related morphotypes.     

Corridors and connectivity: when use and function do not equate

Connectivity, or the integration of populations into a single demographic unit, is an often desired, but largely untested aspect of wildlife corridors. Using a corridor system that was established at least 85 years prior, we investigated the extent of connectivity provided. This was undertaken using a combined ecological and genetic approach with connectivity estimated by gene flow. Vegetation within the corridor was found to be comparable in physical structure and species composition to that within the connected patches and the two target species (Melomys cervinipes and Uromys caudimaculatus) were shown to occur along the corridor but not within the surrounding matrix. These factors indicated that the corridor was suitable for use as a model system. The population structure (weights of individuals, sex ratios and the percentage of juveniles) of both species were also similar within the corridor and the connected patches suggesting that the corridor provided the resources necessary to sustain breeding populations along its length. Despite this, populations in patches linked by the corridor were found to show the same significant levels of genetic differentiation as those in isolated habitats. M. cervinipes, but not U. caudimaculatus, also showed population differentiation within the continuous habitat. Although based on only one corridor system, these results clearly demonstrate that connectivity between connected populations will not always be achieved by the construction or retention of a corridor and that connectivity cannot be inferred solely from the presence of individuals, or breeding populations, within the corridor. C. Wilson: deceased     

半夏不同居群出情况的研究

研究了采自四川各地的不同半夏居群在同一栽培条件下的出苗情况.结果表明:各半夏居群间的出苗率差异显著,出苗期、出苗整齐度差异极显著,且出苗持续时间也有显著差异.采自德阳中江(PT11)的半夏居群出苗率相对较高,出苗较整齐,出苗期较短.由于中江(PT11)半夏的生物碱含量比较低,将其用于大田栽培还需要进行进一步培育和改良;而都江堰(PT18)、资阳(PT7)半夏生物碱含量较高,出苗期较短,出苗较整齐,出苗率较高,采用这2个居群半夏进行栽培,可大大提高栽培效益.