Effect of Periodic Oscillations of Artificial Light Emission on Photosynthetic Activity

The effects of periodic oscillation of artificial light and of the frequency of these oscillations on photosynthetic assimilation has been measured. When the frequency is sufficiently high, the gross CO₂ assimilation in fluctuating light is identical to the assimilation of the leaf under a continuous illumination equal to the efficient intensity of the intermittent light. It is necessary to consider the quality of the sensor used for measuring light intensity, particularly its response velocity.     

Sequence and functional analyses of Haemophilus spp. genomic islands

Background

A major part of horizontal gene transfer that contributes to the diversification and adaptation of bacteria is facilitated by genomic islands. The evolution of these islands is poorly understood. Some progress was made with the identification of a set of phylogenetically related genomic islands among the Proteobacteria, recognized from the investigation of the evolutionary origins of a Haemophilus influenzae antibiotic resistance island, namely ICEHin1056. More clarity comes from this comparative analysis of seven complete sequences of the ICEHin1056 genomic island subfamily.

Results

These genomic islands have core and accessory genes in approximately equal proportion, with none demonstrating recent acquisition from other islands. The number of variable sites within core genes is similar to that found in the host bacteria. Furthermore, the GC content of the core genes is similar to that of the host bacteria (38% to 40%). Most of the core gene content is formed by the syntenic type IV secretion system dependent conjugative module and replicative module. GC content and lack of variable sites indicate that the antibiotic resistance genes were acquired relatively recently. An analysis of conjugation efficiency and antibiotic susceptibility demonstrates that phenotypic expression of genomic island-borne genes differs between different hosts.

Conclusion

Genomic islands of the ICEHin1056 subfamily have a longstanding relationship with H. influenzae and H. parainfluenzae and are co-evolving as semi-autonomous genomes within the 'supragenomes' of their host species. They have promoted bacterial diversity and adaptation through becoming efficient vectors of antibiotic resistance by the recent acquisition of antibiotic resistance transposons.     

The American Isolates: Assimilation, Separation, and Out-Migration in an American Indian Group

The alternative strategies of assimilation, separation, or out-migration which face most rural minority populations are discussed in light of the Mississippi Choctaw experience. Existing in a local society dichotomized between White and Black, the Choctaw response has been similar to that of mestizo groups described by Berry. A combination of employment opportunity, White attitudes, and community size seem to determine which strategy will predominate in a given Choctaw community.     

油杉叶锈研究

油杉叶锈寄生在油杉叶上,作者研究了此菌的模式标本、同引模式标本和后来在模式地区采得的标本;并和柱锈属、金锈属、鞘锈属、栅锈属等11属锈菌作了比较研究。证明这种锈菌冬孢子堆为带状或扁平柱状,无细胞组织垫座,无被;冬孢子可互相撕离而不破裂,孢壁薄而无色,无柄。这些性状说明它不同于柱锈而近于金锈属。因此作者将其转归金锈属,改定为Chrysomyxa keteleeriae(Tai)Wang et Peterson新组合,(基础异名Cronartium keteleeriae Tai)。这种锈菌与其它生在云杉、铁杉叶上的4种短生金锈属锈菌一样,冬孢子堆都生在针叶上,窄带状到扁平柱状或圆形有短柄,鲜桔色或桔红色。虽然油杉叶锈冬孢子堆高达 6mm,但这只是同一属内的种间差别,也象Coleosporium crowellii Cumm。与同属内其它种的区别一样,属于种间的差别。云南粗杉金锈的冬孢子可以从10—20细胞组成的有柄孢子分离产生,正如鞘柄锈冬孢子的互相分离产生一样。冷杉金锈,特别是变形金锈的冬孢子的产生方式也是这样。生在同种油杉寄主枝上的Peridermium kunmingense Jen和油杉叶锈有无关系,需在接种试验后才能肯定。从寄主与寄主菌共同进化关系看,这种锈菌的寄主——油杉在分类系统上与金锈属寄主——云杉、铁杉等属近缘,传统分类学家多认为它同冷杉、银杉、黄杉等属同归冷杉亚科。但也有学者认为油杉有许多原始性状,与冷杉亚科无关。作者在油杉上发现金锈可能支持了传统植物分类系统。     

Genetic differentiation in Philippine bats of the genera Cynopterus and Haplonycteris

Genetic variation and differentiation in six island populations of two species ( Cynopterus brachyotis Müller and Haplonycteris fischeri Lawrence) of Philippine fruit bats (Chiroptera, Pteropodidae) were analysed using allozyme electrophoresis. Cynopterus is eurytopic and widespread in southeast Asia; Haplonycteris is stenotopic and endemic to the Philippines. Genetic variability within populations is consistently higher in Cynopterus , but differentiation between populations is much more pronounced in Haplonycteris. Genetic variation is not significantly correlated with island size in either species, but a positive trend is present in both. Levels of gene flow are sufficiently low to allow differentiation by genetic drift alone in Haplonycteris ( Nm = 0.05), but not in Cynopterus ( Nm = 7.5). There is no significant association between genetic distance and distance between sampling sites; however, between-population differentiation is positively related to degree of geographic isolation during Pleistocene periods of low sea level and to vagility and consequent levels of gene flow among populations. Significant effects of population size on genetic differentiation were not found. Genetic distance matrices for the two species share a common structure that is similar to patterns of mammalian faunal similarity for the Philippines as a whole, suggesting similar effects of geographic and/or environmental factors.