The American brine shrimp as an exotic invasive species in the western Mediterranean

The hypersaline environments and salterns present in the western Mediterranean region (including Italy, southern France, the Iberian Peninsula and Morocco) contain autochthonous forms of the brine shrimp Artemia, with parthenogenetic diploid and tetraploid strains coexisting with the bisexual species A. salina. Introduced populations of the American brine shrimp A. franciscana have also been recorded in these Mediterranean environments since the 1980s. Based on brine shrimp cyst samples collected in these countries from 1980 until 2002, we were able to establish the present distribution of autochthonous brine shrimps and of A. franciscana, which is shown to be an expanding invasive species. The results obtained show that A. franciscana is now the dominant Artemia species in Portuguese salterns, along the French Mediterranean coast and in Cadiz bay (Spain). Co-occurrence of autochthonous (parthenogenetic) and American brine shrimp populations was observed in Morocco (Mar Chica) and France (Aigues Mortes), whereas A. franciscana was not found in Italian cyst samples. The results suggest these exotic A. franciscana populations originate as intentional or non-intentional inoculations through aquacultural (hatchery effluents) or pet market activities, and suggest that the native species can be rapidly replaced by the exotic species. This revised version was published online in July 2006 with corrections to the Cover Date.     

The role of HIV replicative fitness in perinatal transmission of HIV

Perinatal transmission of Human immunodeficiency virus(HIV),also called mother-to-child transmission(MTCT),accounts for 90% of infections in infants worldwide and occurs in 30%-45% of children born to untreated HIV-1 infected mothers.Among HIV-1 infected mothers,some viruses are transmitted from mothers to their infants while others are not.The relationship between virologic properties and the pathogenesis caused by HIV-1 remains unclear.Previous studies have demonstrated that one obvious source of selective pressure in the perinatal transmission of HIV-1 is maternal neutralizing antibodies.Recent studies have shown that viruses which are successfully transmitted to the child have growth advantages over those not transmitted,when those two viruses are grown together.Furthermore,the higher fitness is determined by the gp120 protein of the virus envelope.This suggests that the selective transmission of viruses with higher fitness occurred exclusively,regardless of transmission routes.There are many factors contributing to the selective transmission and HIV replicative fitness is an important one that should not be neglected.This review summarizes current knowledge of the role of HIV replicative fitness in HIV MTCT transmission and the determinants of viral fitness upon MTCT.     

A new species of <Emphasis Type=Italic>Comocladia</Emphasis> (Anacardiaceae) from Belize and Guatemala

Comocladia mayana, a new species of Anacardiaceae, is described, mapped and illustrated. The species is endemic to western Belize and adjacent Guatemala and is restricted to semi-deciduous moist forest on karstic limestone formations. It differs from all other Comocladia species by the combination of entire to subentire, acuminate leaflets and tetramerous staminate flowers.     

Comparative Study of Carbon Storage in Different Forest Stands in Subtropical China

Selection and development of tree species with high fixing CO₂ capacity is an increasing problem worldwide. A comparative study on carbon fixation ability of three forest stands was conducted at Linlong Mountain, Li’nan County, Zhejiang Province, China. The results showed that total carbon storage in the ecosystems of Moso bamboo, Chinese fir, and Masson pine stands were 104.83, 95.66, and 96.49 t C/ha, respectively. The spatial distribution of carbon storage in the three ecosystems decreased in the order: soil > tree story > the vegetation under the forests. Carbon storage in the soils under Moso bamboo, Chinese fir, and Masson pine stands accounted for 65.3, 61.4, and 55.6% of the total CSs, respectively. The Moso bamboo forest ecosystem fixed 1.69 and 1.63 times as much C (9.64 t C/ha/year) as the Chinese fir and Masson pine forest ecosystems, respectively.     

Vegetation of the aquatic and marshland habitats in the Orava region,including the first records of <Emphasis Type=Italic>Potametum alpini,Potametum zizii</Emphasis> and <Emphasis Type=Italic>Ranunculo-Juncetum bulbosi</Emphasis> in the territory of Slovakia

The vegetation of the aquatic and marshland habitats of the Orava region (north of Slovakia) was studied in 2009, using traditional phytosociological methods. Sixteen aquatic and eighteen marsh plant communities were described within 96 phytosociological relevés by using TWINSPAN with the application of the dominance principle. Three associations, Potametum alpini, Potametum zizii and Ranunculo-Juncetum bulbosi, were found as new communities for Slovakia. Myriophylletum verticillati, Potametum nodosi, Potametum graminei and Alisma gramineum community were recorded in the northernmost localities in Slovakia. Among marsh communities, Calletum palustris is very rare, both in the Orava region and in Slovakia as a whole. According to Ellenberg’s indicator values (EIV), moisture was evaluated as the main ecological gradient. Plant communities are ordered along the first Detrended Correspodence Analysis (DCA) axis in a typical hydroseries (Potametea → Lemnetea → Phragmition communis → Phalaridion arundinaceae, Oenanthion aquaticae and Sparganio-Glycerion → Magnocaricion elatae). The second DCA axis was most correlated with EIV for nutrients. Among the five directly measured ecological characteristics (temperature, pH and conductivity of water, water depth, and substrate type), conductivity of water (0.44, P < 0.01) and substrate type (0.32, P < 0.05) were the statistically significant variables explaining the variability along the first DCA axis.     

Population genetics of the cytoplasm and the units of selection on mitochondrial DNA in <Emphasis Type="Italic">Drosophila melanogaster</Emphasis>

Biological variation exists across a nested set of hierarchical levels from nucleotides within genes to populations within species to lineages within the tree of life. How selection acts across this hierarchy is a long-standing question in evolutionary biology. Recent studies have suggested that genome size is influenced largely by the balance of selection, mutation and drift in lineages with different population sizes. Here we use population cage and maternal transmission experiments to identify the relative strength of selection at an individual and cytoplasmic level. No significant trends were observed in the frequency of large (L) and small (S) mtDNAs across 14 generations in population cages. In all replicate cages, new length variants were observed in heteroplasmic states indicating that spontaneous length mutations occurred in these experimental populations. Heteroplasmic flies carrying L genomes were more frequent than those carrying S genomes suggesting an asymmetric mutation dynamic from larger to smaller mtDNAs. Mother-offspring transmission of heteroplasmy showed that the L mtDNA increased in frequency within flies both between and within generations despite sampling drift of the same intensity as occurred in population cages. These results suggest that selection for mtDNA size is stronger at the cytoplasmic than at the organismal level. The fixation of novel mtDNAs within and between species requires a transient intracellular heteroplasmic stage. The balance of population genetic forces at the cytoplasmic and individual levels governs the units of selection on mtDNA, and has implications for evolutionary inference as well as for the effects of mtDNA mutations on fitness, disease and aging.     

Characterization and identification of Sox2+ radial glia cells derived from rat embryonic cerebral cortex

During the central nervous system (CNS) development, radial glia cells (RGCs) play at least two essential roles, they contribute to neuronal production and the subsequent guidance of neuronal migration, whereas its precise distribution and contribution to cerebral cortex remains less understood. In this research, we used Vimentin as an astroglial marker and Sox2 as a neural progenitor marker to identify and investigate RGCs in rat cerebral cortex at embryonic day (E) 16.5. We found that the Sox2+ progenitor cells localized in the germinal zone (GZ) of E16.5 cerebral cortex, ~95% Sox2+ cells co-localized with Vimentin+ or Nestin+ radial processes which extended to the pial surface across the cortical plate (CP). In vitro, we obtained RG-like cells from E16.5 cerebral cortex on adherent conditions, these Sox2+ Radial glia (RG)-like cells shared some properties with RGCs in vivo, and these Sox2+ RG-like cells could differentiate into astrocytes, oligodendrocytes and presented the radial glia—neuron lineage differentiation ability. Taken together, we identified and investigated some characterizations and properties of Sox2+ RGCs derived from E16.5 cerebral cortex, we suggested that the embryonic Sox2+ progenitor cells which located in the cortical GZ were mainly composed of Sox2+ RGCs, and the cortex-derived Sox2+ RG-like cells displayed the radial glia—neuron lineage differentiation ability as neuronal progenitors in vitro.     

Shoot organogenesis and plant regeneration in <Emphasis Type="Italic">Pityopsis ruthii</Emphasis>

Pityopsis ruthii is an endangered herbaceous perennial species from the United States. In vitro multiplication of this species can be valuable for germplasm conservation. Flower receptacles of P. ruthii were cultured on Murashige and Skoog medium (MS) supplemented with 11.4 μM indole-3-acetic acid (IAA) in combination with 2.2, 4.4 or 8.8 μM 6-benzyladenine (BA). Shoots were visible within 14–28 days and three plants were successfully rooted on MS medium supplemented with 5.7 μM IAA. A two tailed t-test for paired-variates revealed that shoot regeneration on MS medium amended with 11.4 μM IAA and 2.2 μM BA was significantly higher (P < 0.05) than on other treatments. Leaf explants were also cultured on MS not supplemented with growth regulators or supplemented with 11.4 μM IAA in combination with 0, 2.2, 4.4 or 8.8 μM BA. Shoots were visible within 21–35 days and one plant was successfully rooted on MS medium supplemented with 5.4 μM NAA. Shoot regeneration on MS medium augmented with 11.4 μM IAA and 2.2 μM BA was significantly higher (P < 0.05) than the other treatments according to analysis of variance (ANOVA) with a rank transformation. Hyperhydricity and rooting of shoots was problematic for explants derived from flower receptacles and leaf tissue, but viable plants were regenerated using both explants sources indicating the potential role for micropropagation in the ex situ conservation of the species.     

Towards a global database of weed risk assessments: a test of transferability for the tropics

Worldwide spread and establishment of alien plant species continues to accelerate and damage ecological and agricultural systems. Early warning and prevention of high-risk introductions is the most cost-effective approach to minimise losses while maximising benefits, and the Australian Weed Risk Assessment (A-WRA) system has been the most well-developed and successful predictive scheme. However, any system would be limited if the results or scores were confined to the locality of assessment. We compiled A-WRA scores conducted in four tropical to sub-tropical regions and tested the accuracy of these scores for predicting naturalisations for a separate well-documented, equatorial, exotic flora where weed risk assessments have never been conducted. Receiver Operating Characteristic (ROC) curves reflect high accuracies of predictions, comparable to those in other studies. No significant differences in accuracy were found between each regional subset and the compiled set of scores. Our results show that A-WRA scores assessed at one locality can be used for others of similar climate, increasing the utility of every species’ assessment. A global database of A-WRA scores would enable rapid local decision-making in border controls on imported plant species. A growing record of species assessments would also facilitate monitoring evolutionary and ecological aspects of invasive species.     

Removal of nitrate-N by antibiotic exposed bacterial isolates from constructed wetlands

Nitrate-N-removing bacterial strains were isolated from a constructed wetland soil treated with three ionophoric antibiotics: monensin, salinomycin and narasin. Five isolates were selected after initial screening for nitrogen removing potential. Nucleotide sequence analysis of the 16S rRNA gene showed that these isolates were highly similar to Bacillus, and Pseudomonas species. The isolates were assessed for their ability to grow in the presence of ionophoric antibiotics. All strains were found to withstand these pharmaceuticals. In particular, Bacillus subtilis strain BRAZ2B was found to thrive in the drug-exposed wetland environment, showing higher nitrate removal rate than the uninoculated control. The strains were also assessed for nitrogen removal potential under three different C/N ratios: 4, 8 and 12; optimum removal efficiency was observed at C/N 8 for most isolates.