Evidence for the mechanisms of zinc uptake by rice using isotope fractionation

In an earlier study, we found that rice (Oryza sativa) grown in nutrient solution well‐supplied with Zn preferentially took up light ⁶⁴Zn over ⁶⁶Zn, probably as a result of kinetic fractionation in membrane transport processes. Here, we measure isotope fractionation by rice in a submerged Zn‐deficient soil with and without Zn fertilizer. We grew the same genotype as in the nutrient solution study plus low‐Zn tolerant and intolerant lines from a recombinant inbred population. In contrast to the nutrient solution, in soil with Zn fertilizer we found little or heavy isotopic enrichment in the plants relative to plant‐available Zn in the soil, and in soil without Zn fertilizer we found consistently heavy enrichment, particularly in the low‐Zn tolerant line. These observations are only explicable by complexation of Zn by a complexing agent released from the roots and uptake of the complexed Zn by specific root transporters. We show with a mathematical model that, for realistic rates of secretion of the phytosiderophore deoxymugineic acid (DMA) by rice, and realistic parameters for the Zn‐solubilizing effect of DMA in soil, solubilization and uptake by this mechanism is necessary and sufficient to account for the measured Zn uptake and the differences between genotypes.     

Invertebrate community structure and ecosystem functioning in European conifer plantation streams

1. Terrestrial leaf‐litter is the dominant energy input to many headwater streams and consequently the nature of the riparian vegetation can have profound effects on in‐stream processes. The impact of conifer plantations on community structure and ecosystem functioning (litter breakdown) was investigated in field experiments in three countries (Britain, Ireland, Poland), each representing a distinct European ecoregion. Twenty‐six streams were used in the trial: half were bordered with broadleaved and the other half with conifer riparian vegetation. 2. In a leaf breakdown study using litter bags, two leaf types (oak and alder) were used to assess the impact of resource quality and two mesh sizes (10 and 0.5 mm aperture) were used to gauge the relative importance of invertebrate detritivores and microbial decomposers respectively. Comparisons were made between vegetation types and among regions; pH varied among individual streams but, unlike many previous studies, it was not confounded with vegetation type, enabling us to isolate the effect of vegetation more effectively. 3. Overall, riparian vegetation type did not affect breakdown rates but strong regional differences were observed. There was also a significant interaction between these two variables, but this disappeared after fitting pH as a covariable, demonstrating its importance in determining breakdown rates and raising the possibility that in previous studies the impacts of conifer plantations might have been confounded with pH. 4. Shredder species composition differed between vegetation types. Small stoneflies were most strongly associated with conifer streams; broadleaved streams generally had a higher proportion of larger taxa, such as limnephilid caddisflies and gammarid shrimps, although the latter were excluded from sites with low pH. However, breakdown rates were maintained irrespective of shredder community composition, suggesting a high degree of functional redundancy in these communities. Similar processing rates were observed between streams with high numbers of nemourids and those with only a few limnephilids or gammarids, suggesting that density compensation among consumers might stabilise process rates. 5. Our results suggest that leaf‐litter breakdown can be an effective proxy for assessing stream ecosystem functioning, as rates differed significantly across spatial scales, from between streams to across regions and responded to an environmental gradient (pH). The litter bag technique can also complement traditional assessment methods by providing valuable information on the composition of consumer guilds, thereby providing an important link between structure and function that is needed to help inform management practices.     

Vulnerability of African mammals to anthropogenic climate change under conservative land transformation assumptions

Recent observations show that human‐induced climate change (CC) and land transformation (LT) are threatening wildlife globally. Thus, there is a need to assess the sensitivity of wildlife on large spatial scales and evaluate whether national parks (NPs), a key conservation tools used to protect species, will meet their mandate under future CC and LT conditions. Here, we assess the sensitivity of 277 mammals at African scale to CC at 10′ resolution, using static LT assumptions in a ‘first‐cut’ estimate, in the absence of credible future LT trends. We examine the relationship between species' current distribution and macroclimatic variables using generalized additive models, and include LT indirectly as a filter. Future projections are derived using two CC scenarios (for 2050 and 2080) to estimate the spatial patterns of loss and gain in species richness that might ultimately result. We then apply the IUCN Red List criteria A3(c) of potential range loss to evaluate species sensitivity. We finally estimate the sensitivity of 141 NPs in terms of both species richness and turnover. Assuming no spread of species, 10–15% of the species are projected to fall within the critically endangered or extinct categories by 2050 and between 25% and 40% by 2080. Assuming unlimited species spread, less extreme results show proportions dropping to approximately 10–20% by 2080. Spatial patterns of richness loss and gain show contrasting latitudinal patterns with a westward range shift of species around the species‐rich equatorial zone in central Africa, and an eastward shift in southern Africa, mainly because of latitudinal aridity gradients across these ecological transition zones. Xeric shrubland NPs may face significant richness losses not compensated by species influxes. Other NPs might expect substantial losses and influxes of species. On balance, the NPs might ultimately realize a substantial shift in the mammalian species composition of a magnitude unprecedented in recent geological time. To conclude, the effects of global CC and LT on wildlife communities may be most noticeable not as a loss of species from their current ranges, but instead as a fundamental change in community composition.     

4号染色体短臂微卫星多态性与鼻咽癌相关性的研究

鼻咽癌（NPC）是一种多因素复杂疾病。其发病过程涉及EB病毒慢性感染、环境致癌因素及宿主基因之间的相互作用。在这一过程中,那些宿主基因在EB病毒感染及鼻咽癌的发生发展中起了关键作用仍不清楚。 本研究的目的是发现与鼻咽癌发生发展中两个关键步骤相关的遗传变异,即EB病毒持续性感染鼻咽部上皮细胞和鼻咽癌的形成。我们在广西梧州市及苍梧县鼻咽癌高发区收集汉族鼻咽癌患者350例、EB病毒壳抗原IgA抗体阳性者(IgA/VCA+)288例和EB病毒壳抗原IgA抗体阴性者(IgA/VCA-)346例。对先前鼻咽癌家系研究显示的鼻咽癌易感区4号染色体短臂（4p15.1-q12）进行了微卫星精细扫描,在 18 Mb的范围内选择34个微卫星标记,包括319个等位基因,对其进行基因分型。比较分析NPC 组和IgA/VCA+组等位基因频率结果显示,9个等位基因与鼻咽癌呈相关,其中5个为易感等位基因（OR=1.51-5.36, p=0.01-0.03）,4个为限制性等位基因（OR值为0.3-0.71, p值为0.02-0.045）。比较分析IgA/VCA+组和IgA/VCA-组及比较所有IgA/VCA+者（包括NPC患者）和IgA/VCA-者等位基因频率的结果显示,12个等位基因与EB病毒壳抗原IgA抗体持续存在相关,其中3个在两组比较中均呈显著相关。等位基因 D4S3241-136 (p=0.004, OR=1.9, 95%CI=1.2-3.0) 和D4S3347-213 (p=0.001, OR=1.6, 95%CI=1.2-2.1) 可增加EB病毒 IgA/VCA抗体形成的危险,为易感基因;而等位基因D4S174-202 (p=0.001, OR=0.5, 95%CI=0.3-0.7) 可限制IgA/VCA抗体的形成。 但上述结果经多因素比较校正后,均失去相关性。我们的研究结果不能 确定该区域与鼻咽癌的形成相关,而另一个家系研究的结果也未得出相关的结果,但本研究却提供了进一步发现鼻咽癌相关基因的研究模式。有关4号染色体短臂 与EB病毒慢性持续感染及鼻咽癌的形成仍值得进一步深入研究。     

Colonization, population expansion, and lineage turnover: phylogeography of Mesoamerican characiform fish

We present a phylogeographical analysis of four genera of Mesoamerican primary freshwater fish ( Brycon , Bryconamericus , Eretmobrycon , and Cyphocharax ). Three hundred and thirty-nine individuals were genotyped into one of 31 operational taxonomic units (OTUs) based on the nucleotide sequence of their mitochondrial ATPase 6 & 8 genes (842–839 bp). Contrary to inference based on the species-level taxonomy of these genera, molecular data identified only a single case of sympatry between closely related OTUs, despite extensive parapatry. Polytomies dominate the mtDNA-based phylogenies and demonstrate multiple, noncontemporaneous waves of rapid expansion across Mesoamerica from South American sources. Analyses based on genetic distances observed among congeneric species of Mesoamerican primary freshwater fishes in comparison to divergence between transisthmian marine fishes permit the strong inference that the Pliocene rise of the Panama land bridge provided the first opportunity for the colonization of Mesoamerica by Characiform fishes. We develop a priority-effect model, based on the assumption that genetically closely related OTUs share similar ecological niches, to reconcile the general lack of contemporary sympatry between closely related OTUs with the substantial historical connectivity among Mesoamerican drainages demonstrated by the rapid expansion of Brycon , Bryconamericus , and Cyphocharax . Finally, in most cases, we infer that the westerly limits of freshwater fish distributions in Mesoamerica are more consistent with being defined by ecological factors rather than by dispersal limitation.  © 2006 The Linnean Society of London, Biological Journal of the Linnean Society , 2006, 88 , 235–255.     

COMPARISONS BETWEEN PALAEOCENE–EOCENE PARATROPICAL SWAMP AND MARGINAL MARINE POLLEN FLORAS FROM ALABAMA AND MISSISSIPPI, USA

Abstract:  Climate warming at the Palaeocene/Eocene boundary ( c . 55.8 Ma) had significant permanent affects on paratropical and warm-adapted vegetation types. Pollen and spore records which document vegetation turnover from the eastern US Gulf Coast have all been taken from sediments of marginal marine depositional environments. Pollen and spores (sporomorphs) are preserved excellently in these marginal marine depositional environments but these assemblages contain grains transported from many different vegetation types and over huge geographic distances. Currently it is unclear whether the turnover from important paratropical areas like the US Gulf Coast is a reflection on actual vegetation change in the local region or from source areas far away in the continental interior. Sporomorph data from 20 former swamps (lignites) from the Nanafalia, Tuscahoma and Hatchetigbee formations in Mississippi and Alabama, USA, are used to test the fidelity of the marine sporomorph record across the Palaeocene–Eocene transition. Data show that extinction is noted in the swamp record (≥7 per cent of Palaeocene taxa) and that swamps were susceptible to immigration in the Early Eocene with the first occurrences of Brosipollis spp. (Burseraceae), Dicolpopollis spp. (Palmae), Nuxpollenites psilatus (Loranthaceae) and Platycarya spp. (Juglandaceae). Swamps have higher within-sample diversity in the Eocene but higher among-sample diversity in latest Palaeocene–earliest Eocene samples, which parallels exactly diversity trends estimated from marine sporomorph assemblages. Palms also increase in abundance in the Eocene. The swamp data demonstrate that the flora growing in these ancient paratropical forests was diverse ( c. 120 taxonomic groups) but incorporated an unusual admixture of plants with modern tropical affinities together with those that now live in modern temperate to subtropical North America.