Discovery of a large clonal patch of a social amoeba: implications for social evolution

Studies of genetic population structures of clonally reproducing macro-organisms have revealed large areas where only one clone is found. These areas, referred to as clonal patches, have not been shown to occur in free-living microbes until now. In free-living microbes, high genetic diversity at local scales is usually maintained by high rates of dispersal. We report, however, a highly dense, 12-m clonal patch of the social amoeba Dictyostelium discoideum in a cattle pasture located in a Texas Gulf Coast prairie. We confirm the presence of only one clone by the analysis of 65 samples and amplification of 10 polymorphic microsatellite loci. Samplings of additional cattle pastures nearby showed higher clonal diversity, but with a density of D. discoideum isolates lower than in the clonal patch. These findings show that high rates of microbial dispersal do not always produce genetic diversity at local scales, contrary to the findings of previous studies. The existence of clonal patches may be particularly important for microbial social evolution.     

Biological activity of aryl hydrocarbon receptor ligands in sediments from remote European lakes

1. Sediment extracts from 63 European remote lakes were tested for the presence of ligands of the aryl hydrocarbon receptor (AhR), using a yeast-based bioassay. The lakes belong to different European mountain regions in Central Norway, Scotland, Piedmont (Italy), Tyrol (Austria and Italy) and the Julian Alps (Slovenia).
2. AhR ligand activity varied about 40-fold among the examined lakes, with Scotland having the highest proportion of lakes with high AhR ligand activity, whereas samples with low AhR ligand activity predominate in the Julian Alps.
3. AhR ligand activity in sediment samples correlated with the concentration of several environmentally relevant compounds, including polycyclic aromatic hydrocarbons, hexachlorobenzene and several polychlorobiphenyl ether congeners. These correlations suggest an anthropogenic origin for the detected AhR ligands, rather than being generated from natural processes.
4. We conclude that pollutants deposited in remote lakes by atmospheric processes are active AhR ligands at the concentrations found in these lakes. Given the high toxicity associated with ectopic activation of AhR in different animal systems, this activity may represent a significant risk for the exposed fauna.     

Impact of intentionally injected carbon dioxide hydrate on deep-sea benthic foraminiferal survival

Sequestration of carbon dioxide (CO₂) in the ocean is being considered as a feasible mechanism to mitigate the alarming rate in its atmospheric rise. Little is known, however, about how the resulting hypercapnia and ocean acidification may affect marine fauna. In an effort to understand better the protistan reaction to such an environmental perturbation, the survivorship of benthic foraminifera, which is a prevalent group of protists, was studied in response to deep-sea CO₂ release. The survival response of calcareous, agglutinated, and thecate foraminifera was determined in two experiments at ∼3.1 and 3.3 km water depth in Monterey Bay (California, USA). Approximately 5 weeks after initial seafloor CO₂ release, in situ incubations of the live–dead indicator CellTracker Green were executed within seafloor-emplaced pushcores. Experimental treatments included direct exposure to CO₂ hydrate, two levels of lesser exposure adjacent to CO₂ hydrate, and controls, which were far removed from the CO₂ hydrate release. Results indicate that survivorship rates of agglutinated and thecate foraminifera were not significantly impacted by direct exposure but the survivorship of calcareous foraminifera was significantly lower in direct exposure treatments compared with controls. Observations suggest that, if large scale CO₂ sequestration is enacted on the deep-sea floor, survival of two major groups of this prevalent protistan taxon will likely not be severely impacted, while calcareous foraminifera will face considerable challenges to maintain their benthic populations in areas directly exposed to CO₂ hydrate.     

Faster returns on ‘leaf economics’ and different biogeochemical niche in invasive compared with native plant species

Plant‐invasive success is one of the most important current global changes in the biosphere. To understand which factors explain such success, we compared the foliar traits of 41 native and 47 alien‐invasive plant species in Oahu Island (Hawaii), a location with a highly endemic flora that has evolved in isolation and is currently vulnerable to invasions by exotic plant species. Foliar traits, which in most cases presented significant phylogenetic signal, i.e. closely related species tended to resemble each other due to shared ancestry, separated invasive from native species. Invasive species had lower leaf mass per area and enhanced capacities in terms of productivity (photosynthetic capacity) and nutrient capture both of macro‐ (N, P, K) and microelements (Fe, Ni, Cu and Zn). All these differences remain highly significant after removing the effects of phylogenetic history. Alien‐invasive species did not show higher efficiency at using limiting nutrient resources, but they got faster leaf economics returns and occupied a different biogeochemical niche, which helps to explain the success of invasive plants and suggests that potential increases in soil nutrient availability might favor further invasive plant success.     

New or rare chromosome counts in the genus Artemisia L. (Asteraceae, Anthemideae) from Armenia and Iran

Nineteen chromosome counts of 12 Artemisia species are reported from Armenia and Iran. Three of them are new reports, sewn are not consistent with previous counts and the remaining are confirmations of very scarce (one to three) previous data. Two basic chromosome numbers (x = 8 and 9) were found, each with several ploidy levels. Chromosome number reduction arising from fusion homozygosity was noted, confirming earlier studies.     

Myrosinase in Sinapis alba L.

Extracts from developing seeds, seedings, and different organsof mature plants of Sinapis alba L. were tested for the presenceof myrosinase. Three different patterns of isoenzymes were distinguishedby isoelectric focusing. One was found in developing seeds andseedlings, a second in mature leaves, stems, flowers, and podsand a third in roots. Sections of all the parts tested were examined for the presenceof myrosin cells by light microscopy. Developing seeds and seedlingsshowed a good correlation between the appearance of myrosinaseand the presence of myrosin cells. No myrosin cells were foundin root or flower parts although they showed myrosinase activity.     

Oligonucleotide Sequence of Replicase Initiation Site in Qβ RNA

THE single stranded RNA genome of bacteriophage Qβ has been variously estimated to consist of from 3,500¹ to 4,500² nucleotides. It contains three known cistrons³, which correspond to three of the four Qβ-specific proteins synthesized in vivo and in vitro^4–6. These are: (1) the gene for the maturation or A protein (molecular weight 41,000 (refs. 4, 5)), (2) that for the major coat protein of the virus (molecular weight 14,000 (ref. 9)) and (3) the gene for the phage-specific subunit of the Qβ replicase (molecular weight 64,000 (ref. 10) or 69,000 (ref. 24)), listed in the probable order^7,8 that they occur on the Qβ RNA. The fourth Qβ-specific protein, A₁ or IIb (molecular weight 36,000 (refs. 4–6, 10)), has recently been shown by Weiner and Weber to have an N-terminal sequence which is identical (for eight amino-acids) to that of the coat protein⁷. Because increased amounts of A₁ appear in virus particles grown in cells containing a UGA suppressor, Weiner and Weber postulate⁷ that this protein is the product of natural read-through at the UGA termination signal of the Qβ coat cistron. Such read-through (involving about 600 nucleotides) could occur entirely within a large “intercistronic” region between the coat and replicase genes, or could involve translation, either in or out of phase, of the replicase cistron. In hopes of distinguishing between these alternatives, I have isolated and examined the nucleotide sequence of the region surrounding the initiator codon of the Qβ replicase gene.     

THE CONTROL OF CERTAIN PLANT DISEASES WITH SULPHONAMIDES

In in vitro tests, sulphanilamide was more toxic to plant pathogenic fungi than to bacterial plant pathogens, but sulphadiazine and other heterocyclic-ring substituted compounds were more toxic to plant pathogenic bacteria than to fungi. When tested in vivo against a number of facultative plant parasites the sulphonamides were without effect except in providing slight control of Pseudomonas coronafaciens on oats. Against a number of obligate parasites including Uromyces fabae on broad beans and Puccinia triticina on wheat, the sulphonamides gave effective control when applied either through the roots or leaves. The minimal effective concentrations in the leaves of the more active compounds varied between 100–200 μg./g. fresh weight of leaf tissue.
The sulphonamides are also toxic to higher plants and both the fungitoxic and phytotoxic effects could be reversed with p -aminobenzoic acid.
A number of sulphanilamides with acyl substituents on the p -amino-group were tested against P. triticina and were shown to control the disease with very slight phytotoxic damage. Control could be attributed to the release of 'free' sulphanilamide by hydrolysis within the plant.
Two factors appear to control the systemic action of sulphonamides: first, the movement in the plant which results in the accumulation of effective concentrations in the leaves, and secondly, the specificity of a sulphonamide for a particular host-parasite association.     

A COMPARATIVE STUDY OF THE GROWTH OF WILD OATS (AVENA FATUA L. AND A. LUDOVICIANA DUR.) AND OF CULTIVATED CEREALS WITH VARIED NITROGEN SUPPLY

Growth analysis of wild oats ( Avena fatua and A. ludoviciana ) grown in pots with different levels of nitrogen supply showed many similarities to spring barley, winter oats and winter wheat.
Small differences that could affect competition between wild oats and cereals occurred mainly in the seedlings. Wild oat seedlings were smaller than the corresponding cultivated cereals in total dry weight, total nitrogen content, leaf area and number of shoots. However, very young wild oat plants had higher net assimilation rates than the cultivated cereals and soon caught up and passed them. The difference in net assimilation rate did not persist, and in the later stages of growth differences in dry-matter production depended mainly on differences in leaf area. Another important difference between wild oats and cultivated cereals was that 98–100% of the wild oat seeds and none of the crop seeds were dormant 2 months after harvest.
Ear emergence in wild oats spread over a longer period, the range of ear heights was greater and the tallest ears were taller than in the corresponding cultivated cereals. Assimilation in the ear appeared to account for less of the total dry matter of the plants of wild and cultivated oats than of wheat. The wild oats produced more seeds per plant than the cultivated cereals, but the 1000-grain weight, and hence the total dry weight of seeds, was lower in the weeds than in the crop.
Addition of nitrogen to the soil affected the growth of the wild oats in the same ways as the cultivated cereals; they took up the same amount of nitrogen per plant as winter oats and winter wheat but more than spring barley.
It is concluded that wild oats are most susceptible in the seedling stage to competition from the crop and that nitrogenous fertilizer applied to an infested field is unlikely to alter the balance between the yields of crop and of wild oats.