Expression Preference of the S-adenosylmethionine Synthetase (Sam-S) Gene in Drosophila melanogaster

Ｓ－腺苷甲硫氨酸合成酶（ＳａｍＳ）是目前已知的唯一在生物体内催化腺苷甲硫氨酸合成的酶。它是除自身以外、所有甲基化反应的甲基供体,并且参与多胺的生物合成。多胺对于稳定ＤＮＡ、ＲＮＡ和蛋白质大分子的双螺旋结构具有重要作用,和ＤＮＡ的甲基化一起参与了基因组的印迹（ｉｍｐｒｉｔｉｎｇ）过程。在分离到ＳａｍＳ基因的基础上,本文通过Ｎｏｒｔｈｅｒｎｂｌｏｔ和酶活两种方法,对该基因在野生型果蝇和四个等位突变体发育过程中主要阶段的转录和转译水平进行了测定。野生型果蝇由瑞典Ｕｍｅａ大学果蝇中心提供。由于该基因的突变是阴性致死突变,研究中采用了杂合子突变体：Ｓｕ（ｚ）５,Ｌ（２）Ｍ６,Ｌ（２）Ｒ２３和Ｄｆ（２Ｌ）ＰＭ４４,均由所在实验室诱变获得。Ｎｏｒｔｈｅｒｎ分析时,以ｃＤＮＡ＃１０和ａ微管蛋白基因为探针,分析果蝇卵巢、幼虫、蛹、胚胎、雄性和雌性成蝇中该基因Ｐｏｌｙ（Ａ）ＲＮＡ的转录水平。通过测定蛋白粗提物中的酶活,分析果蝇卵巢、幼虫、蛹、以及雄性成蝇腹部组织中该基因的翻译水平。Ｆｉｇ．１,２＆３表明：ＳａｍＳ基因主要在成熟雌蝇的卵巢中高表达,在雄性成蝇中该基因的表达水平明显低于雌性。在其它发育阶段及组织部位中仅维持     

Migration of herbaceous plant species across ancient–recent forest ecotones in central Belgium

1 We studied the migration of forest plant species using their percentage cover and frequency in 197 plots distributed over 26 transects across ecotones between ancient and recent deciduous forests in the Meerdaal forest complex in central Belgium. The recent forest stands varied in age between 36 and 132 years, and all occurred on silty, well-drained soils.
2 The total cover, number and diversity of field layer species did not differ significantly between ancient and recent forest stands.
3 The number and cover of the ancient forest plant species and of ant-dispersed species correlated positively with the age of the recent forest and negatively with both the duration of its former agricultural land use and the distance to the ancient forest. This implies a slow colonization of the recent forest stands by these species; all species were, however, able to migrate across the ecotones.
4 The cover of four species ( Anemone nemorosa , Lamium galeobdolon , Convallaria majalis and Polygonatum multiflorum ) declined along the transect, suggesting that they are limited by seed dispersal. Their colonization rates, calculated from the occurrence of the farthest individual, ranged from < 0.05 to 1.15 m year⁻¹ and for other measures from < 0.05 to 0.65 m year⁻¹. Anemone and Lamium appeared to colonize the recent forest by establishment of isolated individuals, while Polygonatum and Convallaria expanded populations from existing patches on the border between ancient and recent forest.
5 Several forest species were able to colonize the recent forest rapidly, where some of them even reached a higher abundance, due to the increased availability of colonization sites with a higher nutrient content and a thinner organic layer.     

Fish drift in a Danube sidearm‐system: II. Seasonal and diurnal patterns

Seasonal and diurnal patterns of larval and juvenile fish drift were investigated in the Marchfeldkanal, a man‐made side branch of the Danube River near Vienna, Austria. A clear seasonal pattern with peak densities in mid‐June was found. Species composition varied over time, showed a site specific pattern and was dominated by tubenose goby Proterorhinus marmoratus . Water temperature was the main factor responsible for the increase of drift densities until the median drift date and repeated occurrence of early larval stages in drift indicated repeated spawning for many species. Significant differences in drift densities between different time periods of the day (day, dusk, night and dawn) were found for common bream Abramis brama , barbel Barbus barbus , chub Leuciscus cephalus , tubenose goby and roach Rutilus rutilus . The highest drift rates occurred at night (2200–0400 hours), with 86% of all larvae drifting during the hours of darkness. Fish larvae of different lengths drifting at different phases of the day were found for common bream, bleak Alburnus alburnus and chub, with largest larvae drifting during dusk (chub) and day (bleak and common bream). For bleak, all gudgeon species Gobio spp., tubenose goby, roach and for all cyprinid species combined, one 2 h night sample was found to be sufficient to predict the total 24 h drift.     

Historical biogeography of Hexabathynella , a cosmopolitan genus of groundwater Syncarida (Crustacea, Bathynellacea, Parabathynellidae)

Hexabathynella is the only cosmopolitan genus of the order Bathynellacea (Crustacea). The known species number 18, found in Europe (9), Africa (1), South America (2), North America (3) and Australia and New Zealand (3). Phylogenetic analysis suggests that the least derived species are those from South America and the most derived those from the Iberian Peninsula, North America and Australia. The five species with the most plesiomorphic characters occur in salt or brackish water, which supports a marine origin for the genus. Phylogenetic and biogeographical analyses suggest that the distribution of the genus can be explained by dispersion and a double vicariant biogeographical model based on plate tectonics and the evolution of the Tethys during the Mesozoic and Cenozoic.  © 2003 The Linnean Society of London . Biological Journal of the Linnean Society , 2003, 78 , 457–466.     

Effect of strain-specific hypersensitive resistance on spatial patterns of virus spread

Spatial patterns of spread were compared between strains of Bean yellow mosaic virus (BYMV) that differ in causing systemic necrotic (hypersensitive) or non‐necrotic symptoms in narrow‐leafed lupin (Lupinus angustifolius). Both types of BYMV were spread naturally by aphids from adjacent infected pasture into a large lupin block (‘natural spread site’), or from clover plants introduced as virus sources into two field experiments with lupin. Cumulative spatial data for plants with disease symptoms from a range of times in the growing period were assessed using Spatial Analysis by Distance IndicEs (SADIE). At the‘natural spread site’, with non‐necrotic BYMV, the extent of clustering of plants with symptoms increased gradually over time, while with necrotic BYMV there was less clustering and no increase over time. In both experiments, for the type of BYMV that was introduced into a plot, there was a gradual increase in clustering, but with this being greater with non‐necrotic BYMV. In the second experiment, there was also significant clustering of plants with symptoms of non‐necrotic BYMV in plots without introduced non‐necrotic foci but not for necrotic BYMV in plots without introduced necrotic foci. When clustering data for plants with newly recorded symptoms was tested for spatial association between successive assessment dates, association was positive for both BYMV types though stronger for the non‐necrotic type, declining as the temporal lag increased. Generally, association was strongest for assessments 2–3 wk apart, corresponding approximately to the period for BYMV to move systemically in plants and for obvious symptoms to appear in shoot tips. Contour maps for local association between dates showed that the strongest spatial associations were from coincidence of infection gaps rather than infection patches. The combination of information from clustering and association analysis showed that spread of non‐necrotic BYMV is less diffuse, with considerably more localised infection surrounding the infection sources. This work demonstrates how spatial virus spread can be diminished when hypersensitive (necrotic) resistance is deployed, and the limitations associated with employing hypersensitivity that is strain specific.     

Primary Seed Dispersal by Red Howler Monkeys and the Effect of Defecation Patterns on the Fate of Dispersed Seeds1

The effectiveness of a seed disperser depends on the quantity and quality of dispersal. The quality of dispersal depends in large part on factors that affect the post–dispersal fate of seeds, and yet this aspect of dispersal quality is rarely assessed. In the particular case of seed dispersal through endozoochory, the defecation pattern produced has the potential of affecting the fate of dispersed seeds and consequently, dispersal quality and effectiveness. In this study, I assessed the effects of dung presence and dung/seed densities on seed predation by rodents and secondary dispersal by dung beetles. In particular, I compared seed fates in clumped defecation patterns, as those produced by howler monkeys, with seed fates in scattered defecation patterns, as those produced by other frugivores. I also determined the prevalence of red howler monkeys (Alouatta seniculus) as seed dispersers at the plant community level in Central Amazonia by determining the number of species they dispersed in a 25–month period. I found that dung presence and amount affected rodent and dung beetle behavior. Seed predation rates were higher when dung was present, and when it was in higher densities. The same number of seeds was buried by dung beedes, in dumped versus scattered defecation patterns, but more seeds were buried when they were inside large dung–piles versus small piles. Seed density had no effect on rodent or dung beetle behavior. Results indicate that caution should be taken when categorizing an animal as a high or low quality seed disperser before carefully examining the factors that affect the fate of dispersed seeds. Red howler monkeys dispersed the seeds of 137 species during the study period, which is the highest yet reported number for an Alouatta species, and should thus be considered highly prevalent seed dispersers at the plant community level in Central Amazonian terra firme rain forests.     

THE ECOLOGICAL IMPLICATIONS OF GROWTH FORMS IN EPIBENTHIC DIATOMS 1

This paper evaluates the utilisation of space by epibenthic diatom cells, as a response to environmental variations. The aggregation pattern of five species of epibenthic diatoms was quantified and compared to provide evidence for the significance of cell motility as an adaptive mechanism for space occupation and monopoly. The epibenthic diatoms included (1) non-mobile colonial species forming either fan-shaped (Synedra tabulata (Ag)Kz.) or arborescent (Gomphonema kamtschaticum var. californicum Grun.) colonies; (2) slow-moving (Cocconeis costata Greg, and Amphora pusio Cl.), and (3) fast-moving (Navicula direct a (W. Sm.) Ra.) non-colonial species. The aggregation pattern of S. tabulata did not vary significantly among six different light intensities manipulated in nature. The major patterns of aggregation were identified using analysis of covariance and dummy-variable regression. Highly mobile N. directa are significantly less aggregated than the four other diatom species. Non-mobile and slow-moving species show a similar, highly aggregated pattern. The occurrence of two patterns of spatial dispersion indicates that growth forms bear far-ranging ecological implications with respect to colonization strategies, immigration, and possibly impact by grazers. An integrated model of growth form characteristics, biological properties, and ecological implications is presented for epibenthic diatoms.     

Behavioral investigation of the coexistence of substance P,corticotropin releasing factor,and acetylcholinesterase in lateral dorsal tegmental neurons projecting to the medial frontal cortex of the rat

Colocalization of substance P (SP), corticotropin releasing factor (CRF), and acetylcholinesterase (AChE) was detected by retrograde tracing and immunocytochemical staining in the nucleus tegmentalis dorsalis lateralis (ntdl) projecting to the medial frontal cortex (MFC), septum, and thalamus of the rat. The histochemical results suggest that SP and CRF coexist within a subpopulation of ntdl cholinergic neurons that project to a number of forebrain regions including the MFC. Behavioral studies of the effects of SP, CRF, and the cholinergic agonist, carbachol, employed microinjections into the MFC of rats. SP and CRF did not elicit any behavioral effects when administered alone. Carbachol (1–5 μg/side) produced a stereotyped motor behavior, consisting of rapid forepaw treading while in an upright posture, resembling “boxing.” SP (1 μg/side) increased carbachol-induced “boxing.” CRF (1–10 ng/side) decreased carbachol-induced “boxing.” One possible functional significance of the coexistence of SP, CRF, and acetylcholinesterase, in neurons projecting to the medial frontal cortex in rats, appears to be a modulatory potentiation of cholinergic response by SP, and a modulatory inhibition of the cholinergic response by CRF.     

Spatial patterns of leaf nutrient traits of the plants in the Loess Plateau of China

The spatial patterns of leaf nutrient traits of plants in seven sites, Yangling, Yongshou, Tongchuan, Fuxian, Ansai, Mizhi and Shenmu, standing from south to north in the Loess Plateau of China, were studied. The results showed that of the 126 plant samples in the Loess Plateau, the mean leaf organic carbon (C), nitrogen (N), phosphorus (P) and potassium (K) were 43.8, 2.41, 0.16 and 1.67%, respectively, and ranked in the order of C > N > K > P. Leaf C, N, P and K ranged from 32.6 to 54.8%, 0.82 to 4.58%, 0.06 to 0.35%, and 0.24 to 4.21%, respectively. The mean leaf C/N, C/P and N/P ratios were 21.2, 312 and 15.4, respectively. It is indicated that leaf N in the Loess Plateau was significantly higher than those in Chinese and global flora, but leaf P was significantly lower than that in global flora, which resulted in a higher N/P ratio in the Loess Plateau. The results also showed that leaf C, N, P, K, C/N and C/P ratios varied significantly among the seven life-form groups, which were trees, shrubs, herbages, evergreen trees, deciduous trees, C₃ and C₄ herbages, but leaf N/P ratio differed little among the seven life-forms. In the sampled species in the Loess Plateau, leaf C was negatively correlated with leaf N, P and K, while leaf N, P and K were positively correlated with one another. In general, leaf N/P ratio increased as the latitude and annual solar radiation increased and the mean annual rainfall and mean annual temperature decreased.     

Use of host plants by Troidini butterflies (Papilionidae, Papilioninae): constraints on host shift

Molecular phylogenetic analyses were conducted to determine relationships and to investigate character evolution for the Troidini/Aristolochia interaction, in an attempt to answer the following questions: (1) what is the present pattern of use of Aristolochia by these butterflies; (2) is the pattern we see today related to the phylogeny of plants or to their chemical composition; (3) can the geographical distribution of Aristolochia explain the host plant use observed today; and (4) how did the interaction between Troidini and Aristolochia evolve? Analyses of character optimization suggest that the current pattern of host plant use of these butterflies does not seem to be constrained by the phylogeny of their food plants, neither by the secondary chemicals in these plants nor by their geographical similarity. The current host plant use in these butterflies seems to be simply opportunistic, with species with a wider geographical range using more species of host plants than those with a more restricted distribution. © 2007 The Linnean Society of London, Biological Journal of the Linnean Society, 2007, 90 , 247–261.