Connectivity in a pond system influences migration and genetic structure in threespine stickleback

Neutral genetic structure of natural populations is primarily influenced by migration (the movement of individuals and, subsequently, their genes) and drift (the statistical chance of losing genetic diversity over time). Migration between populations is influenced by several factors, including individual behavior, physical barriers, and environmental heterogeneity among populations. However, drift is expected to be stronger in populations with low immigration rate and small effective population size. With the technological advancement in geological information systems and spatial analysis tools, landscape genetics now allows the development of realistic migration models and increased insight to important processes influencing diversity of natural populations. In this study, we investigated the relationship between landscape connectivity and genetic distance of threespine stickleback (Gasterosteus aculeatus) inhabiting a pond complex in Belgjarskógur, Northeast Iceland. We used two landscape genetic approaches (i.e., least-cost-path and isolation-by-resistance) and asked whether gene flow, as measured by genetic distance, was more strongly associated with Euclidean distance (isolation-by-distance) or with landscape connectivity provided by areas prone to flooding (as indicated by Carex sp. cover)? We found substantial genetic structure across the study area, with pairwise genetic distances among populations (D_PS) ranging from 0.118 to 0.488. Genetic distances among populations were more strongly correlated with least-cost-path and isolation-by-resistance than with Euclidean distance, whereas the relative contribution of isolation-by-resistance and Euclidian distance could not be disentangled. These results indicate that migration among stickleback populations occurs via periodically flooded areas. Overall, this study highlights the importance of transient landscape elements influencing migration and genetic structure of populations at small spatial scales.     

Growth and age determination of the tropical Australian cubozoan Chiropsalmus sp.

Chiropsalmus sp. medusae collected in this study ranged from 3 to 71 mm diagonal bell width and displayed growth best described by the following equation size (mm) = 74.9 × exp (−exp(0.041 (time since metamorphosis (day) −35.6674))). Growth rates of up to 7 mm week⁻¹ increase in diagonal bell width are theoretically possible, with animals able to reach sexual maturity in approximately 70 days. Correlation of the number of rings on the statoliths with the predicted age of the individual from the field produced a relationship that indicates the growth rings are laid down daily and as such could be used to infer age of the medusae. Over the 1998–1999 season, there were four influxes of juvenile cohorts, each occurring approximately 14 days after a major rainfall event.     

Extension of Drosophila melanogaster life span with a GPCR peptide inhibitor

G protein-coupled receptors (GPCRs) mediate signaling from extracellular ligands to intracellular signal transduction proteins. Methuselah (Mth) is a class B (secretin-like) GPCR, a family typified by their large, ligand-binding, N-terminal extracellular domains. Downregulation of mth increases the life span of Drosophila melanogaster; inhibitors of Mth signaling should therefore enhance longevity. We used mRNA display selection to identify high-affinity (K(d) = 15 to 30 nM) peptide ligands that bind to the N-terminal ectodomain of Mth. The selected peptides are potent antagonists of Mth signaling, and structural studies suggest that they perturb the interface between the Mth ecto- and transmembrane domains. Flies constitutively expressing a Mth antagonist peptide have a robust life span extension, which suggests that the peptides inhibit Mth signaling in vivo. Our work thus provides new life span-extending ligands for a metazoan and a general approach for the design of modulators of this important class of GPCRs.     

Accurate and Rapid Identification of the Burkholderia pseudomallei Near-Neighbour,Burkholderia ubonensis,Using Real-Time PCR

Burkholderia ubonensis is an environmental bacterium belonging to the Burkholderia cepacia complex (Bcc), a group of genetically related organisms that are associated with opportunistic but generally nonfatal infections in healthy individuals. In contrast, the near-neighbour species Burkholderia pseudomallei causes melioidosis, a disease that can be fatal in up to 95% of cases if left untreated. B. ubonensis is frequently misidentified as B. pseudomallei from soil samples using selective culturing on Ashdown’s medium, reflecting both the shared environmental niche and morphological similarities of these species. Additionally, B. ubonensis shows potential as an important biocontrol agent in B. pseudomallei-endemic regions as certain strains possess antagonistic properties towards B. pseudomallei. Current methods for characterising B. ubonensis are laborious, time-consuming and costly, and as such this bacterium remains poorly studied. The aim of our study was to develop a rapid and inexpensive real-time PCR-based assay specific for B. ubonensis. We demonstrate that a novel B. ubonensis-specific assay, Bu550, accurately differentiates B. ubonensis from B. pseudomallei and other species that grow on selective Ashdown’s agar. We anticipate that Bu550 will catalyse research on B. ubonensis by enabling rapid identification of this organism from Ashdown’s-positive colonies that are not B. pseudomallei.     

Diverse populations of lake water bacteria exhibit chemotaxis towards inorganic nutrients

Chemotaxis allows microorganisms to rapidly respond to different environmental stimuli; however, understanding of this process is limited by conventional assays, which typically focus on the response of single axenic cultures to given compounds. In this study, we used a modified capillary assay coupled with flow cytometry and 16S rRNA gene amplicon pyrosequencing to enumerate and identify populations within a lake water microbial community that exhibited chemotaxis towards ammonium, nitrate and phosphate. All compounds elicited chemotactic responses from populations within the lake water, with members of Sphingobacteriales exhibiting the strongest responses to nitrate and phosphate, and representatives of the Variovorax, Actinobacteria ACK-M1 and Methylophilaceae exhibiting the strongest responses to ammonium. Our results suggest that chemotaxis towards inorganic substrates may influence the rates of biogeochemical processes.     

Down-regulation of two non-homologous endogenous tomato genes with a single chimaeric sense gene construct

Tomatoes (Lycopersicon esculentum Mill cv. Ailsa Craig) were transformed with a gene construct having 244 bp of the 5 end of a polygalacturonase (PG) cDNA, coding for a 71 amino acid N-terminal extension to the mature protein, fused to 1320 bp of a pectinesterase (PE) cDNA encoding the full sequence of the mature PE protein. This chimaeric gene was inserted in a sense orientation between a CaMV 35S promoter and terminator for constitutive expression. In transformed tomato plants expression of the endogenous PG and PE genes in the fruit was inhibited; there was little or no observable PG and PE mRNA and a substantial reduction in the level of PG and PE enzyme activity. The transgene was expressed in the leaves of the transformed plants as demonstrated by the accumulation of mRNA, but no protein product could be identified. However, no transgene mRNA or protein were observed in the transgenic fruit.This paper represents the first report of the down-regulation of two non-homologous endogenous genes using a single gene construct. A sense gene construct was responsible for these effects. These findings are discussed in relation to possible mechanisms of action of co-suppression.     

Pattern of respiration by intact inflorescences of the thermogenic arum lily Philodendron selloum

Inflorescences of the neotropical arum lily, Philodendron selloum, are strongly thermogenic for 2 d during anthesis. Continuous measurements of spadix temperature (Ts) and rate of oxygen consumption (VO2) were made outdoors in whole inflorescences attached to the plants. Some inflorescences were exposed to uncontrolled ambient temperature (Ta) while others were enclosed in clear water-jackets that produced nearly constant ambient conditions. A repeatable, diphasic pattern of heat production appeared, most clearly in water-jacketed inflorescences, and it comprised a short peak phase at sunset followed by a plateau phase that lasted until the following sunset. Regulation of Ta occurred in both phases, but at different levels. Peak phase Ta was regulated in the region of 38-42C, but plateau phase Ta was usually in the range of 25-36C. Both VO2 and total heat produced throughout anthesis increased at lower Ta. The data imply that the short peak phase is related to the enhancement of odour production that attracts a single species of large scarabaeid beetle in its native Brazil, and regulation of maximum Ta may prevent overheating. Thermoregulation in the long plateau phase produces equable temperatures inside the inflorescence that may facilitate the resident beetles' activities as a direct energetic reward.     

Characterisation of the binding interaction between poly(L-lysine) and DNA using the fluorescamine assay in the preparation of non-viral gene delivery vectors

A major factor limiting the development of non-viral gene delivery systems is the poor characterisation of polyelectrolyte complexes formed between cationic polymers and DNA. The present study uses the fluorescamine reagent to improve characterisation of poly(L-lysine) (pLL)/DNA complexes post-modified with a multivalent hydrophilic polymer by determining the availability of free amino groups. The results show that the fluorescamine reagent can be used to monitor the self-assembly reaction between pLL and DNA and the degree of surface modification of the resultant complexes with a hydrophilic polymer. This experimental approach should enable the preparation of fully defined complexes whose properties can be better related to their biological activity.