A Global History of Australian Trees

Scholars studying the globalization of Australian trees have previously emphasized the rapid natural propagation of Australian trees outside of their native habitats, believing their success to be a reversal of “ecological imperialism” from the “new world” to the “old world.” This article argues that the expansion of Australian trees should not be viewed as a biological phenomenon, but as the result of a long-term attempt by powerful states and state-sponsored scientists to select and breed Australian species that could grow in a variety of climates and ecological conditions. Five non-biological factors largely determined the success of these attempts to grow Australian trees: the abundance or paucity of natural forests, state power, the amount of scientific research directed to planting Australian trees, the cost of labor, and the ability to utilize hardwood timbers and bark. This paper compares the use of Australian trees in Australia, India, and South Africa to demonstrate that biology was not the determining factor in the long-term success of many Australian genera and species.     

In vitro characterization of a gamma-secretase radiotracer in mammalian brain

Inhibition of gamma-secretase is a potential therapeutic target for Alzheimer's disease (AD). The present studies have characterized the in vitro properties of a radiolabeled small molecule gamma-secretase inhibitor, [3H]compound D (Yan et al., 2004, J. Neurosci.24, 2942-2952) in mammalian brain. [3H]Compound D was shown to bind with nanomolar affinity (Kd = 0.32-1.5 nM) to a single population of saturable sites in rat, rhesus and human brain cortex homogenates, the density of binding sites ranging from 4 to 7 nM across the species. Competition studies with a structurally diverse group of gamma-secretase inhibitors with a wide range of binding affinities showed that the binding affinities of these compounds correlated well with their ability to inhibit gamma-secretase in vitro. Autoradiographic studies showed that the specific binding of [3H]compound D was widely distributed throughout adult rat, rhesus and normal human brain. There did not appear to be any difference in distribution of [3H]compound D specific binding sites in AD cortex compared with control human cortex as measured using tissue section autoradiography, nor any correlation between gamma-secretase binding and plaque burden as measured immunohistochemically. [3H]compound D is a useful tool to probe the expression and pharmacology of gamma-secretase in mammalian brain.     

Oxysterol-binding protein (OSBP) enhances replication of intracellular Salmonella and binds the Salmonella SPI-2 effector SseL via its N-terminus

Effectors translocated into the host cell by Salmonella enterica serovar Typhimurium are critical for bacterial virulence. For many effectors, the mechanisms of their interactions with host pathways are not yet understood. We have recently found an interaction between the SPI-2 effector SseL and oxysterol-binding protein (OSBP). We show here that SseL binds the N-terminus of OSBP and that S. Typhimurium infection results in redistribution of OSBP. We furthermore demonstrate that OSBP is required for efficient replication of intracellular S. Typhimurium. This suggests that S. Typhimurium hijacks OSBP-dependent pathways to benefit its intracellular life-style, possibly by SseL- and OSBP-mediated manipulation of host lipid metabolism.     

Islands within islands: a molecular phylogenetic study of the Leucocroton alliance (Euphorbiaceae) across the Caribbean Islands and within the serpentinite archipelago of Cuba

Aim Our aim was to investigate the historical biogeography of the three genera of the Leucocroton alliance (i.e. Garciadelia Jestrow & Jiménez Rodr., Lasiocroton Griseb., and Leucocroton Griseb., Euphorbiaceae). Location  The alliance is restricted to the Bahamas, Cuba, Hispaniola and Jamaica. Methods Members of the Leucocroton alliance, along with representatives from tribe Adelieae (Adelia L. and Philyra Klotzsch.), were included in a molecular phylogenetic analysis based upon nucleotide sequences of the internal transcribed spacer region of the nuclear ribosomal DNA and the non‐coding chloroplast regions psbM–trnD and ycf6–pcbM. The program s‐diva was used to calculate ancestral areas based on the phylogenetic trees and present species distributions. Results Phylogenetic analyses support the monophyly of the three genera. The ancestral area of the Leucocroton alliance is eastern Cuba and Hispaniola. Ancestral forms of Leucocroton arose on eastern Cuba and underwent two migrations across the island. The ancestor of Lasiocroton also originated on eastern Cuba followed by later dispersal to and speciation events on the other islands. Our study also suggests that ancestral forms of the Leucocroton alliance probably occurred on limestone soils. Main conclusions Our study concurs with previous hypotheses suggesting that the flora of serpentinite regions of the Caribbean derives from other types of soils. The serpentine endemics of the Leucocroton alliance have a single origin and represent one of the most extraordinary examples of speciation in this unique environment of the New World. The high colonization success achieved by the members of Leucocroton on serpentine soils was not attained by the other genera of the alliance, which occur on limestone areas.     

Generalist predator's niche shifts reveal ecosystem changes in an experimentally fragmented landscape

Habitat fragmentation can alter the trophic structure of communities and environmental conditions, thus driving changes in biodiversity and ecosystem functions. Quantifying niches of generalist predators can reveal how fragmentation alters ecosystems. In a habitat fragmentation experiment, we used stable isotopes of a generalist predator skink to test predictions from spatial theory on trophic structure and to quantify abiotic changes associated with fragmentation among continuous forest, fragments, and matrix habitats. We predicted that in fragments and the matrix, isotopic niches would shift due to decreases in skink trophic positions (δ¹⁵N) from reductions in trophic structure of arthropod food webs and abiotic changes over time (δ¹³C) relative to continuous forest. Contrary to theoretical predictions, we did not find evidence of reductions in trophic structure with fragmentation. In fact, skink δ¹⁵N values were higher in the matrix and fragments than continuous forest, likely due to changes in distributions of a detritivorous prey species. In addition, δ¹³C values in the matrix decreased over years since fragmentation due to abiotic changes associated with matrix tree maturation. We show how isotopic niches are influenced by fragmentation via shifts in biotic and abiotic processes. The potential for either or both spatial and abiotic effects of fragmentation present a challenge for theory to better predict ecological changes in fragmented landscapes.     

Effects of short-term chemical ablation of the GIP receptor on insulin secretion, islet morphology and glucose homeostasis in mice

Glucose-dependent insulinotropic polypeptide (GIP) is an incretin hormone secreted by endocrine K-cells in response to nutrient absorption. In this study we have utilized a specific and enzymatically stable GIP receptor antagonist, (Pro3)GIP, to evaluate the contribution of endogenous GIP to insulin secretion and glucose homeostasis in mice. Daily injection of (Pro3)GIP (25 nmol/kg body weight) for 11 days had no effect on food intake or body weight. Non-fasting plasma glucose concentrations were significantly raised (p<0.05) by day 11, while plasma insulin concentrations were not significantly different from saline treated controls. After 11 days, intraperitoneal glucose tolerance was significantly impaired in the (Pro3)GIP treated mice compared to control (p<0.01). Glucose-mediated insulin secretion was not significantly different between the two groups. Insulin sensitivity of 11-day (Pro3)GIP treated mice was slightly impaired 60 min post injection compared with controls. Following a 15 min refeeding period in 18 h fasted mice, food intake was not significantly different in (Pro3)GIP treated mice and controls. However, (Pro3)GIP treated mice displayed significantly elevated plasma glucose levels 30 and 60 min post feeding (p<0.05, in both cases). Postprandial insulin secretion was not significantly different and no changes in pancreatic insulin content or islet morphology were observed in (Pro3)GIP treated mice. The observed biological effects of (Pro3)GIP were reversed following cessation of treatment for 9 days. These data indicate that ablation of GIP signaling causes a readily reversible glucose intolerance without appreciable change of insulin secretion.     

Molecular characterization of Clostridium perfringens isolates from humans with sporadic diarrhea: evidence for transcriptional regulation of the beta2-toxin-encoding gene

Clostridium perfringens type A food poisoning is caused by C. perfringens isolates carrying a chromosomal enterotoxin gene (cpe), while non-food-borne gastrointestinal (GI) diseases, such as antibiotic-associated diarrhea (AAD) and sporadic diarrhea (SD), are caused by C. perfringens plasmid cpe isolates. A recent study reported the association of beta2 toxin (CPB2) with human GI diseases, and particularly AAD/SD, by demonstrating that a large percentage of AAD/SD isolates, in contrast to a small percentage of food poisoning isolates, carry the beta2-toxin gene (cpb2). This putative relationship was further tested in the current study by characterizing 14 cpe+ C. perfringens fecal isolates associated with recent cases of human SD in England (referred to hereafter as SD isolates). These SD isolates were all classified as cpe+ type A, and 12 of the 14 cpe+ isolates carry their cpe gene on the plasmid and 2 carry it on the chromosome. Interestingly, cpb2 is present in only 12 plasmid cpe isolates; 11 isolates carry cpe and cpb2 on different plasmids, but cpe and cpb2 are located on the same plasmid in one isolate. C. perfringens enterotoxin is produced by all 14 cpe+ SD isolates. However, only 10 of the 12 cpe+/cpb2+ SD isolates produced CPB2, with significant variation in amounts. The levels of cpb2 mRNA in low- to high-CPB2-producing SD isolates differed to such an extent (30-fold) that this difference could be considered a major cause of the differential level of CPB2 production in vitro by SD isolates. Furthermore, no silent or atypical cpb2 was found in a CPB2 Western blot-negative isolate, 5422/94, suggesting that the lack of CPB2 production in 5422/94 was due to low expression of cpb2 mRNA. This received support from our observation that the recombinant plasmid carrying 5422/94 cpb2, which overexpressed cpb2 mRNA, restored CPB2 production in F4969 (a cpb2-negative isolate). Collectively, our present results suggest that CPB2 merits further study as an accessory toxin in C. perfringens-associated SD.     

A Field Evaluation of an External and Neutrally Buoyant Acoustic Transmitter for Juvenile Salmon: Implications for Estimating Hydroturbine Passage Survival

Turbine-passed fish are exposed to rapid decreases in pressure which can cause barotrauma. The presence of an implanted telemetry tag increases the likelihood of injury or death from exposure to pressure changes, thus potentially biasing studies evaluating survival of turbine-passed fish. Therefore, a neutrally buoyant externally attached tag was developed to eliminate this bias in turbine passage studies. This new tag was designed not to add excess mass in water or take up space in the coelom, having an effective tag burden of zero with the goal of reducing pressure related biases to turbine survival studies. To determine if this new tag affects fish performance or susceptibility to predation, it was evaluated in the field relative to internally implanted acoustic transmitters (JSATS; Juvenile Salmon Acoustic Telemetry System) used widely for survival studies of juvenile salmonids. Survival and travel time through the study reach was compared between fish with either tag type in an area of high predation in the Snake and Columbia rivers, Washington. An additional group of fish affixed with neutrally-buoyant dummy external tags were implanted with passive integrated transponder (PIT) tags and recovered further downstream to assess external tag retention and injury. There were no significant differences in survival to the first detection site, 12 river kilometers (rkm) downstream of release. Travel times were also similar between groups. Conversely, externally-tagged fish had reduced survival (or elevated tag loss) to the second detection site, 65 rkm downstream. In addition, the retention study revealed that tag loss was first observed in fish recaptured approximately 9 days after release. Results suggest that this new tag may be viable for short term (<8 days) single-dam turbine-passage studies and under these situations, may alleviate the turbine passage-related bias encountered when using internal tags, however further research is needed to confirm this.     

The Interactions of Vibrio vulnificus and the Oyster Crassostrea virginica

The human bacterial pathogen, Vibrio vulnificus, is found in brackish waters and is concentrated by filter-feeding molluscan shellfish, especially oysters, which inhabit those waters. Ingestion of raw or undercooked oysters containing virulent strains of V. vulnificus can result in rapid septicemia and death in 50 % of victims. This review summarizes the current knowledge of the environmental interactions between these two organisms, including the effects of salinity and temperature on colonization, uptake, and depuration rates of various phenotypes and genotypes of the bacterium, and host–microbe immunological interactions.