Impact of Land-use Change on Dengue and Malaria in Northern Thailand

Land-use change, a major constituent of global environmental change, potentially has significant consequences for human health in relation to mosquito-borne diseases. Land-use change can influence mosquito habitat, and therefore the distribution and abundance of vectors, and land use mediates human–mosquito interactions, including biting rate. Based on a conceptual model linking the landscape, people, and mosquitoes, this interdisciplinary study focused on the impacts of changes in land use on dengue and malaria vectors and dengue transmission in northern Thailand. Extensive data on mosquito presence and abundance, land-use change, and infection risk determinants were collected over 3 years. The results of the different components of the study were then integrated through a set of equations linking land use to disease via mosquito abundance. The impacts of a number of plausible scenarios for future land-use changes in the region, and of concomitant behavioral change were assessed. Results indicated that land-use changes have a detectable impact on mosquito populations and on infection. This impact varies according to the local environment but can be counteracted by adoption of preventive measures.     

Intra-annual genetic variation in the downstream larval drift of sutchi catfish (Pangasianodon hypophthalmus) in the Mekong river

Larvae of the sutchi catfish Pangasianodon hypophthalmus were collected during peak downstream drift in the Lower Mekong river on four occasions over an 8-week period during the 2003 spawning season, and genotyped using seven microsatellite loci. We provide evidence for several heterogeneous groups within and among the temporally discrete larval peak samples. Strong evidence for a significant deficit of heterozygotes was observed for each larval sample and the pooled sample, possibly due to population admixture. Although individual-based assignment tests suggested that each larval peak sample was admixed, significant but low genetic differentiation was observed among larval samples ( F _ST = 0.0052, P  < 0.01). The lack of significant relatedness confirms the multifamily composition of each larval group, excluding family bias to explain the observed genetic heterogeneity. Both the entire larval peak and each temporally separated larval peak originated from spawning groups with heterogeneous allelic composition involving several distinct spawning events. We propose three explanations to account for our findings: (1) the ecological match/mismatch hypothesis; (2) the genetic 'sweepstakes' selection hypothesis; and (3) life-history-specific characteristics of the spawning populations. Finally, an intra-annual shift in the contribution of the spawning populations to the larval drift was detected on successive occasions.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 89 , 719–728.     

Geographic distribution of the invasive cattle tick Rhipicephalus microplus, a country-wide survey in Benin

The cattle tick Rhipicephalus microplus is currently invading the West African region, and little information is available on the spread of this exotic tick in this region. We set out a country-wide field survey to determine its current distribution in Benin. Ticks were collected on cattle from 106 farms selected by random sampling covering all regions of the country. Rhipicephalus annulatus was found on 70?% of all farms, R. decoloratus on 42?%, R. geigyi on 58?%, and R. microplus on 49?%. There is a clear geographic separation between the indigenous Rhipicephalus species and R. microplus. Rhipicephalus annulatus occurs mainly in the northern departments, but it was also observed in lower numbers in locations in the south. The presence of R. decoloratus is limited to the northern region, and in most locations, this tick makes up a small proportion of the collected ticks. The tick R. geigyi tends to be dominant, but occurs only in the four northern departments. The observations concerning R. microplus are entirely different, this species occurs in the southern and central region. The results of this survey confirm the invasive character and displacement properties of R. microplus, since in less than a decade it has colonized more than half of the country and has displaced indigenous ticks of the same genus in many of the sampled locations.     

Insecticidal activities of Ginkgo biloba seed coat extracts against Spodoptera exigua (Lepidoptera: Noctuidae)

The present study relates to a methanol extract of the seed coat of Ginkgo biloba, and tested particularly on the third instar larvae of Spodoptera exigua. The extract was found to have an inhibitory effect on the growth of the larvae besides bringing a change in the nutrient reserves in the body of the insect. Topical application of five different doses of the methanol extract resulted in a mortal effect to third instar larvae of S. exigua that is very much dependent on the dose as well as duration of exposure. Lower doses revealed lower mortality after 24 h of application. At doses of 1.00, 2.00, 4.00, 8.00 and 16.00 ng/larva, mortalities were 9.25, 26.07, 50.32, 56.28 and 92.44%, respectively. The dose for 50% mortality (LD₅₀) of methanol extracts by applied by a topical method with 1 µL of acetone solution was 1.92 ng/larva. Nutrient reserves like protein, glycogen and lipid are known to regulate pupation and adult emergence. These reserves have been found to be lower in treated larvae, indicating the insecticidal role of methanol extracts from G. biloba against third instar larvae of S. exigua.     

Riccia fruticulosa O.F.Müll., 1782 and blue Metzgeria (Marchantiophyta) in Europe

Riccia fruticulosa O.F.Müll., 1782 from Norway is a valid name, referring to Riccardia palmata (Hedw.) Carruth. In 1785 Dickson misidentified British plants of a blue Metzgeria as R. fruticulosa . The European blue species of Metzgeria is conspecific with M. violacea (Ach.) Dumort., which replaces M. fruticulosa auct. The true origin of the type of Jungermannia violacea Ach., 1805 is probably Tierra del Fuego (rather than Dusky Bay, New Zealand), where the species is widespread. Reports from Australasia, Asia and Africa are all erroneous. The blue colour of Jungermanniales is found only in living plants and is derived from the oil-bodies. In contrast, that of Metzgeria appears only after death; its biological function is unknown.  © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society, 2003, 142 , 229−235.     

Variations in the life-history parameters of Hemipyrellia ligurriens (Diptera: Calliphoridae) in response to larval competition for food

Abstract. 1. Larval rearing densities of Hemipyrellia ligurriens (Wiedemann) (Diptera: Calliphoridae) in standardized carrion were manipulated in order to investigate changes in life-history parameters in response to larval competition for food.
2. Competition was of the typical scramble type. Survivorship remained high at densities up to 32 larvae g liver^-1 but decreased rapidly as larval density increased further.
3. Emergent adults were undersized with reduced fecundity and longevity. Variations in adult body size apparently reduced the effects of competition on larval mortality.
4. Females of dry weight corresponding to only 10.4% of the potential maximum emerged at the highest rearing densities of 128 larvae g liver-1. However, these females had a nearly four-fold increase in reproductive investment (per unit weight) when compared to the largest individuals.
5. The duration of larval development declined when competition was intense (i.e. at high larval densities).
6. The short adult life of H.ligurriens, combined with the unpredictability of larval habitat availability, may reduce the value of long-range dispersal so that females 'do better' by maintaining reproductive investment despite a concomitant decline in dispersal ability.     

金黄地鼠视皮层通过胼胝体顺行和逆行激活的神经元的电活动和分布

用细胞外记录技术研究了金黄地鼠一侧视皮层神经元对电刺激另一侧相应部位的反应及其对视觉刺激反应的特点。(1)在17—18a 交界区大多数(78%)细胞能被电刺激对侧相应点所驱动。在17区内部,被驱动细胞数随离开17—18a 交界距离增加而减少。(2)按对电刺激的反应形式,记录的细胞可分为四类:a.逆行驱动细胞,占17—18a 交界区记录细胞数的20%;b.顺行驱动细胞,占52%中;c.自发发放因电刺激而减少或完全停止的细胞,占6%,d.其余细胞(22%)对电刺激没有可察觉的反应。(3)在17—18a 交界,除了Ⅰ层以外的各层都可记录到顺行驱动细胞,而逆行驱动细胞则主要集中在Ⅲ及Ⅴ层。(4)17—18a 交界细胞感受野(RF)多位于垂直中线附近的对侧视野内,有些 RF 跨越中线,其边界延伸到同侧约10°处。(5)逆行驱动细胞包括刁和 Blakemore 以前在视皮层中记录到的所有细胞类型和各种程度的眼优势,但单眼细胞的比例增加,非对称式 RF 和中心对称式的给-撤型 RF 的比例有所减少。     

Differentiation-associated modulation of heparan sulfate structure and function in CaCo-2 colon carcinoma cells

Heparan sulfate species expressed by different cell and tissue types differ in their structural and functional properties. Limited information is available on differences in regulation of heparan sulfate biosynthesis within a single tissue or cell population under different conditions. We have approached this question by studying the effect of cell differentiation on the biosynthesis and function of heparan sulfate in human colon carcinoma cells (CaCo-2). These cells undergo spontaneous differentiation in culture when grown on semipermeable supports; the differentiated cells show phenotypic similarity to small intestine enterocytes. Metabolically labeled heparan sulfate was isolated from the apical and basolateral media from cultures of differentiated and undifferentiated cells. Compositional analysis of disaccharides, derived from the contiguous N-sulfated regions of heparan sulfate, indicated a greater proportion of 2-O- sulfated iduronic acid units and a smaller amount of 6-O-sulfated glucosamine units in differentiated than in undifferentiated cells. By contrast, the overall degree of sulfation, the chain length and the size distribution of the N-acetylated regions were similar regardless the differentiation status of the cells. The structural changes were found to affect the binding of heparan sulfate to the long isoform of platelet-derived growth factor A chain but not to fibroblast growth factor 2. These findings show that heparan sulfate structures change during cell differentiation and that heparan sulfate-growth factor interactions may be affected by such changes.