Disentangling invasion processes in a dynamic shipping-boating network

The relative importance of multiple vectors to the initial establishment, spread and population dynamics of invasive species remains poorly understood. This study used molecular methods to clarify the roles of commercial shipping and recreational boating in the invasion by the cosmopolitan tunicate, Botryllus schlosseri. We evaluated (i) single vs. multiple introduction scenarios, (ii) the relative importance of shipping and boating to primary introductions, (iii) the interaction between these vectors for spread (i.e. the presence of a shipping-boating network) and (iv) the role of boating in determining population similarity. Tunicates were sampled from 26 populations along the Nova Scotia, Canada, coast that were exposed to either shipping (i.e. ports) or boating (i.e. marinas) activities. A total of 874 individuals (c. 30 per population) from five ports and 21 marinas was collected and analysed using both mitochondrial cytochrome c oxidase subunit I gene (COI) and 10 nuclear microsatellite markers. The geographical location of multiple hotspot populations indicates that multiple invasions have occurred in Nova Scotia. A loss of genetic diversity from port to marina populations suggests a stronger influence of ships than recreational boats on primary coastal introductions. Population genetic similarity analysis reveals a dependence of marina populations on those that had been previously established in ports. Empirical data on marina connectivity because of boating better explains patterns in population similarities than does natural spread. We conclude that frequent primary introductions arise by ships and that secondary spread occurs gradually thereafter around individual ports, facilitated by recreational boating.     

探索癌基因的成熟年代

1866年,Paul Broca 从他妻子家系的略图中,领悟到癌症的遗传因素。这一洞察所见,在他那时代似乎没有引起人们的注意(实际上,他的想法直至当代仍被 carl Segen 所忽视)。不过一个世纪以来,生物学家们都开始对肿瘤发生寻找遗传方面的解释。目前这个问题所获得的成果是:关于长期设想的“癌基因”已出现在我们的眼前。癌基因的发现首先是由于逆转病毒有转导细胞基因的偏好——正是在正常细胞 DNA 中寻找逆转病毒的癌基因使它实体化了。由此两个进一步的设想又增添到活跃的想象中去:一是逆转病毒DNA 的整合能够触动细胞基因,后者的激活明显地有引起肿瘤发生的作用;二是从各种肿瘤取得的 DNA 能够使啮盘类细胞发生瘤性生长,这种 DNA 似乎含有活     

植物无性杂交的新方法

在1950年苏联医学科学院生物学部举行的生活物质和细胞发展问题的会议上,奥·帕·勒柏辛斯卡娅院士在谈到植物界细胞起源问题时,曾表示任无性杂交的实践中,不用枝条而用植物的汁液嫁接可能性的意见.为了企图使这个可能性成为事实,我在1951年开始试验研碎另一种植物茎的方法得到汁液,注射到茎里去.因为植物组织缺乏弹性的缘故,经过几次失败之     

Diseases and deaths; a summary of data from the Los Angeles County General Hospital, 1918 to 1948

Classification of the 2,557,035 diagnoses made in 1,168,139 different patients at the Los Angeles County General Hospital in the period 1918-48 has been compiled according to the new International List of Causes of Diseases and Death. Similar tabulation of the 377,776 diagnoses made in the 112,409 patients who died while in the hospital reflects the fatality rates associated with these diagnoses. Striking differences are shown in the incidence and fatality rates in the various conditions and great changes have occurred in both during this time. Defects and sources of error in these data are recognized, but they offer a wealth of valuable material for further study and interpretation.