Micro‐particle‐induced X‐ray emission mapping of elemental distribution in roots of a Mediterranean‐type sclerophyll,Agathosma betulina (Berg.) Pillans,colonized by Cryptococcus laurentii

The role of rhizosphere yeasts as plant nutrient‐scavenging microsymbionts in resource‐limited Mediterranean‐type heathlands is unknown. This study, therefore, focused on quantitative elemental distribution within the roots of a medicinal sclerophyll, Agathosma betulina (Berg.) Pillans, grown under nutrient‐poor conditions, and colonized by Cryptococcus laurentii. Micro‐particle‐induced X‐ray emission (PIXE) was used to assess quantitative elemental distribution within the roots of A. betulina inoculated with viable C. laurentii, as well as within roots of control plants that received autoclaved yeast. To aid in the interpretation of heterogeneous elemental distribution patterns, apoplastic barriers (Casparian bands) in root tissues were located using fluorescence microscopy. In addition, root cross‐sections were examined for endophytic C. laurentii using light and transmission electron microscopy (TEM). The average concentrations of P, Fe and Mn were significantly (P < 0.05) higher in roots of yeast‐inoculated plants, compared to control plants. Casparian bands were observed in the exodermal cells of both treatments, and the presence of these bands was correlated with elemental enrichment in the epi/exodermal‐outer cortical tissues. Light and TEM micrographs revealed that the yeast was not a root endophyte. This is the first report describing the role of a soil yeast as a plant nutrient‐scavenging microsymbiont.     

Association between DRD4 gene polymorphism and personality variation in great tits: a test across four wild populations

Polymorphisms in the dopamine receptor D4 gene (DRD4) have been related to individual variation in novelty‐seeking or exploratory behaviour in a variety of animals, including humans. Recently, the human DRD4 orthologue was sequenced in a wild bird, the great tit (Parus major) and a single nucleotide polymorphism in exon 3 of this gene (SNP830) was shown to be associated with variation in exploratory behaviour of lab‐raised individuals originating from a single wild population. Here we test the generality of this finding in a large sample of free‐living individuals from four European great tit populations, including the originally sampled population. We demonstrate that the association between SNP830 genotype and exploratory behaviour also exists in free‐living birds from the original population. However, in the other three populations we found only limited evidence for an association: in two populations the association appeared absent; while in one there was a nonsignificant tendency. We could not confirm a previously demonstrated interaction with another DRD4 polymorphism, a 15 bp indel in the promoter region (ID15). As yet unknown differences in genetic or environmental background could explain why the same genetic polymorphism (SNP830) has a substantial effect on exploratory behaviour in one population, explaining 4.5–5.8% of the total variance—a large effect for a single gene influencing a complex behavioural trait—but not in three others. The confirmation of an association between SNP830 genotype and personality‐related behaviour in a wild bird population warrants further research into potential fitness effects of the polymorphism, while also the population differences in the strength of the association deserve further investigation. Another important future challenge is the identification of additional loci influencing avian personality traits in the wild.     

Identifying footprints of selection in stocked brown trout populations: a spatio‐temporal approach

Studies of interactions between farmed and wild salmonid fishes have suggested reduced fitness of farmed strains in the wild, but evidence for selection at the genic level is lacking. We studied three brown trout populations in Denmark which have been significantly admixed with stocked hatchery trout (19–64%), along with two hatchery strains used for stocking. The wild populations were represented by contemporary samples (2000–2006) and two of them by historical samples (1943–1956). We analysed 61 microsatellite loci, nine of which showed putative functional relationships [expressed sequence tag (EST)‐linked or quantitative trait loci]. F_ST‐based outlier tests provided support for diversifying selection at chromosome regions marked by three loci, two anonymous and one EST‐linked. Patterns of differentiation suggested that the loci were candidates for being under diversifying hitch‐hiking selection in hatchery vs. wild environments. Analysis of hatchery strain admixture proportions showed that in one wild population, two of the loci showed significantly lower admixture proportions than the putatively neutral loci, implying contemporary selection against alleles introduced by hatchery strain trout. In the most strongly admixed population, however, there was no evidence for selection, possibly because of immigration by stocked trout overcoming selection against hatchery‐derived alleles or supportive breeding practices allowing hatchery strain trout to escape natural selection. To our knowledge, this is the first study demonstrating footprints of selection in wild salmonid populations subject to spawning intrusion by farmed fish.     

The role of the kinase OXI1 in cadmium‐ and copper‐induced molecular responses in Arabidopsis thaliana

The hypothesis that mitogen‐activated protein kinase (MAPK) signalling is important in plant defences against metal stress has become accepted in recent years. To test the role of oxidative signal‐inducible kinase (OXI1) in metal‐induced oxidative signalling, the responses of oxi1 knockout lines to environmentally realistic cadmium (Cd) and copper (Cu) concentrations were compared with those of wild‐type plants. A relationship between OXI1 and the activation of lipoxygenases and other initiators of oxylipin production was observed under these stress conditions, suggesting that lipoxygenase‐1 may be a downstream component of OXI1 signalling. Metal‐specific differences in OXI1 action were observed. For example, OXI1 was required for the up‐regulation of antioxidative defences such as catalase in leaves and Fe‐superoxide dismutase in roots, following exposure to Cu, processes that may involve the MEKK1‐MKK2‐WRKY25 cascade. Moreover, the induction of Cu/Zn superoxide dismutases in Cu‐exposed leaves was regulated by OXI1 in a manner that involves fluctuations in the expression of miRNA398. These observations contrast markedly with the responses to Cd exposure, which also involves OXI1‐independent pathways but rather involves changes in components mediating intracellular communication.     

Impacts of Argentine ants on mealybugs and their natural enemies in California's coastal vineyards

Abstract 1. The Argentine ant, Linepithema humile, tends honeydew‐excreting homopterans and can disrupt the activity of their natural enemies. This mutualism is often cited for increases in homopteran densities; however, the ant’s impact on natural enemies may be only one of several effects of ant tending that alters insect densities. To test for the variable impacts of ants, mealybug and natural enemy densities were monitored on ant‐tended and ant‐excluded vines in two California vineyard regions. 2. Ant tending increased densities of the obscure mealybug, Pseudococcus viburni, and lowered densities of its encyrtid parasitoids Pseudaphycus flavidulus and Leptomastix epona. Differences in parasitoid recovery rates suggest that P. flavidulus was better able to forage on ant‐tended vines than L. epona. 3. Densities of a coccinellid predator, Cryptolaemus montrouzieri, were higher on ant‐tended vines, where there were more mealybugs. Together with behavioural observations, the results showed that this predator can forage in patches of ant‐tended mealybugs, and that it effectively mimics mealybugs to avoid disturbance by ants. 4. Ant tending increased densities of the grape mealybug, Pseudococcus maritimus, by increasing the number of surviving first‐instar mealybugs. Parasitoids were nearly absent from the vineyard infested with P. maritimus. Therefore, ants improved either mealybug habitat or fitness. 5. There was no difference in mealybug distribution or seasonal development patterns on ant‐tended and ant‐excluded vines, indicating that ants did not move mealybugs to better feeding locations or create a spatial refuge from natural enemies. 6. Results showed that while Argentine ants were clearly associated with increased mealybug densities, it is not a simple matter of disrupting natural enemies. Instead, ant tending includes benefits independent of the effect on natural enemies. Moreover, the effects on different natural enemy species varied, as some species thrive in the presence of ants.     

Pseudoplacentela smirnovi gen. et sp. n. (Tunicata, Ascidiacea), with a discussion of its phylogenetic relationships

Pseudoplacentela smirnovi gen. et sp. n., a colonial ascidian from the Kuril Islands, is described and placed in the holozoidac. The related species Placentela crystallina Redikorzev also seems to belong to the Holozoidae rather than to the Polyclinidae.     

Partial Purification and Characterization of Naegleria fowleriβ-Glucosidase1

Naegleria fowleri cells, grown axenically, contain high levels of β-D-glucosidase which catalyzes the hydrolysis of 4-methylumbelliferyl-β-D-glucopyranoside (4MUGlc) (K_m, 0.9 mM), octyl-β-D-glucoside (K_m, 0.17 mM), and p-nitrophenyl-β-D-glucopyranoside at relative rates of 1.00, 2.88, and 1.16, respectively (substrate concentration, 3.0 mM). When the amebae are subjected to freeze-thawing, sonication, and centrifugation (100,000 g, 1 h), 85% of the β-glucosidase activity appears in the supernatant fraction. The β-glucosidase was purified 40-fold (34% yield) using a combination of chromatographic steps involving DE-52 cellulose, concanavalin A-Sepharose, and hydroxylapatite followed by isoelectric focusing. The predominant soluble β-D-galactosidase activity in the Naegleria extract copurifies with the β-D-glucosidase; the two activities have the same isoelectric point (pI, 6.9), similar heat stabilities, are both inhibited by lactobionic acid (K_i, 0.40 mM), and exhibit optima at pH 4.5, indicating that they are probably the same enzyme. The Naegleriaβ-D-glucosidase has an apparent molecular weight of 66,000, a Stokes radius of 25 Å, and a sedimentation coefficient of 4.2S. The β-glucosidase is not inhibited by conduritol β-epoxide or galactosylsphingosine but is completely inhibited by 1.25 mM bromo conduritol β-epoxide. The latter compound, when present in the growth medium, inhibits the growth of the organism and profoundly alters its ultrastructure, the main effect being the apparent inhibition of cytokinesis and the generation of multinucleate cells. The issue of the role of the β-glucosidase in the metabolism of the ameba and its possible role in pathogenic mechanisms are discussed.     

Where temperate meets tropical: multi-factorial effects of elevated CO2, nitrogen enrichment, and competition on a mangrove-salt marsh community

Our understanding of how elevated CO₂ and interactions with other factors will affect coastal plant communities is limited. Such information is particularly needed for transitional communities where major vegetation types converge. Tropical mangroves (Avicennia germinans) intergrade with temperate salt marshes (Spartina alterniflora) in the northern Gulf of Mexico, and this transitional community represents an important experimental system to test hypotheses about global change impacts on critical ecosystems. We examined the responses of A. germinans (C₃) and S. alterniflora (C₄), grown in monoculture and mixture in mesocosms for 18 months, to interactive effects of atmospheric CO₂ and pore water nitrogen (N) concentrations typical of these marshes. A. germinans, grown without competition from S. alterniflora, increased final biomass (35%) under elevated CO₂ treatment and higher N availability. Growth of A. germinans was severely curtailed, however, when grown in mixture with S. alterniflora, and enrichment with CO₂ and N could not reverse this growth suppression. A field experiment using mangrove seedlings produced by CO₂‐ and N‐enriched trees confirmed that competition from S. alterniflora suppressed growth under natural conditions and further showed that herbivory greatly reduced survival of all seedlings. Thus, mangroves will not supplant marsh vegetation due to elevated CO₂ alone, but instead will require changes in climate, environmental stress, or disturbance to alter the competitive balance between these species. However, where competition and herbivory are low, elevated CO₂ may accelerate mangrove transition from the seedling to sapling stage and also increase above‐ and belowground production of existing mangrove stands, particularly in combination with higher soil N.