Amplification and transport of an endemic fish disease by an introduced species

The introduction of American shad from the Atlantic to the Pacific coast of North America in the late 1800’s and the subsequent population expansion in the 1980’s resulted in the amplification of Ichthyophonus sp., a Mesomycetozoean parasite of wild marine fishes. Sequence analysis of the ribosomal DNA gene complex (small subunit and internal transcribed spacer regions) and Ichthyophonus epidemiological characteristics indicate a low probability that Ichthyophonus was co-introduced with American shad from the Atlantic; rather, Ichthyophonus was likely endemic to marine areas of the Pacific region and amplified by the expanding population of a highly susceptible host species. The migratory life history of shad resulted in the transport of amplified Ichthyophonus from its endemic region in the NE Pacific to the Columbia River watershed. An Ichthyophonus epizootic occurred among American shad in the Columbia River during 2007, when infection prevalence was 72%, and 57% of the infections were scored as moderate or heavy intensities. The epizootic occurred near the record peak of shad biomass in the Columbia River, and corresponded to an influx of 1,595 mt of infected shad tissues into the Columbia River. A high potential for parasite spillback and the establishment of a freshwater Ichthyophonus life cycle in the Columbia River results from currently elevated infection pressures, broad host range, plasticity in Ichthyophonus life history stages, and precedents for establishment of the parasite in other freshwater systems. The results raise questions regarding the risk for sympatric salmonids and the role of Ichthyophonus as a population-limiting factor affecting American shad in the Columbia River.     

Speciation in sexually deceptive orchids: pollinator-driven selection maintains discrete odour phenotypes in hybridizing species

Ophrys orchids mimic the female sex pheromones of their pollinator species to attract males for pollination. Reproductive isolation in Ophrys is based on the selective attraction of only a single pollinator species. A change of floral odour can result in the attraction of a new pollinator species that acts as an isolation barrier towards other sympatrically occurring Ophrys species. Ophrys lupercalis, Ophrys bilunulata, and Ophrys fabrella grow sympatrically and bloom consecutively on Majorca and are pollinated by three species of Andrena. We investigated variation of phenotypic and genotypic flower traits, aiming to study the role of the floral odour for reproductive isolation and speciation. Using chemical and electrophysiology (gas chromatography coupled with an electroantennographic detector) methods, we show that the three Ophrys species use the same odour compounds for pollinator attraction, but in different proportions. A comparison of the floral odour bouquets in a multivariate analysis revealed a clear grouping of plants from the same species, although with an overlap between species. A comparison of the same plants using molecular markers gave a contrasting result. Although O. lupercalis and O. fabrella were genetically well separated, plants of O. bilunulata did not form a distinct group but were similar to either O. lupercalis or O. fabrella. Our data indicate gene flow and hybridization to occur between O. bilunulata and O. lupercalis as well as between O. bilunulata and O. fabrella. All plants of O. bilunulata, despite having different genotypes, showed a very similar floral odour. This reflects a strong selective pressure by the pollinating males. The overlap of genotypes of O. bilunulata and O. fabrella supports our hypothesis that O. fabrella diverged from O. bilunulata by scent variation and the attraction of a new pollinator species, Andrena fabrella. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98 , 439–451.     

The order of DNA replication in mammalian cells : A modified density labelling procedure for isolating sequences replicated at specific times

These experiments were directed towards establishing a procedure for isolation of the DNA sequences replicated at different times in S phase for further study. Primary considerations were thus for a method that gave fairly large quantities of cells as well synchronized in S phase as possible. The use of Chinese hamster ovary (CHO) cells synchronized by isoleucine starvation followed by exposure to hydroxyurea [1] seemed to be most promising and was explored in detail. During the course of this work, a labelling scheme was developed that involved exposure to BrdUrd during the same time window in two sequential S phases. Only those regions of the genome replicated in the same interval in each S period contained BrdUrd in both strands and these were readily isolated in CsCl gradients. As applied in the present experiments, this labelling procedure showed no untoward effects on cell-cycle traverse and gave DNA distributions in density gradients that closely approximated those that would be expected for the conditions employed.     

Day/night differences in pineal indoles in the adult pigeon (Columba livia)

Day/night differences in concentrations of 5-hydroxy and 5-methoxy indole metabolites in the pineal gland of the pigeon are described. A simultaneous determination of 5-hydroxytryptamine (serotonin), 5-hydroxyindoleacetic acid, 5-hydroxytryptophol, N-acetyl-5-hydroxytryptamine (N-acetyl serotonin), 5-methoxyindoleacetic acid, 5-methoxytryptophol, tryptophan, indoleacetic acid and melatonin was accomplished using a recently developed procedure employing high-performance liquid chromatography with electrochemical detection. As in mammalian species, an inverse relationship was observed between N-acetylated indoles and serotonin and its acid metabolites. Melatonin and N-acetyl serotonin were increased approximately three-fold at night to concentrations of 0.730 and 1.79 ng/pineal respectively. Daytime serotonin values were 44.9 +/- 13.0 ng/pineal and decreased to 12.3 +/- 6.5 ng/pineal during the dark phase.     

Triaminopyrimidinium (TAP+) blocks luminal membrane K conductance inNecturus gallbladder epithelium

Summary The effect of triaminopyrimidinium (TAP⁺) on the apical membrane ofNecturus gallbladder epithelial cells was investigated with intracellular microelectrode techniques. TAP⁺, added to the mucosal bathing solution only, produced the following effects (all rapid and reversible): (i) cell depolarization, (ii) increase of apical membrane resistance, and (iii) decrease of the apical membrane potential change produced by K for Na substitution on the mucosal side. These results can be explained by a decrease of apical membrane K conductance. The paracellular effects of TAP⁺ were similar to the ones previously described by Moreno (J.H. Moreno, 1974;Nature (London) 251:150; J.H. Moreno, 1975,J. Gen. Physiol. 66:97). These results indicate that the change of transepithelial potential produced by TAP⁺ cannot be ascribed solely to its effect on the paracellular pathway.     

Simultaneously Capturing Real-time Images in Two Emission Channels Using a Dual Camera Emission Splitting System: Applications to Cell Adhesion

Multi-color immunofluorescence microscopy to detect specific molecules in the cell membrane can be coupled with parallel plate flow chamber assays to investigate mechanisms governing cell adhesion under dynamic flow conditions. For instance, cancer cells labeled with multiple fluorophores can be perfused over a potentially reactive substrate to model mechanisms of cancer metastasis. However, multi-channel single camera systems and color cameras exhibit shortcomings in image acquisition for real-time live cell analysis. To overcome these limitations, we used a dual camera emission splitting system to simultaneously capture real-time image sequences of fluorescently labeled cells in the flow chamber. Dual camera emission splitting systems filter defined wavelength ranges into two monochrome CCD cameras, thereby simultaneously capturing two spatially identical but fluorophore-specific images. Subsequently, psuedocolored one-channel images are combined into a single real-time merged sequence that can reveal multiple target molecules on cells moving rapidly across a region of interest.     

Cooperative navigation in robotic swarms

We study cooperative navigation for robotic swarms in the context of a general event-servicing scenario. In the scenario, one or more events need to be serviced at specific locations by robots with the required skills. We focus on the question of how the swarm can inform its members about events, and guide robots to event locations. We propose a solution based on delay-tolerant wireless communications: by forwarding navigation information between them, robots cooperatively guide each other towards event locations. Such a collaborative approach leverages on the swarm’s intrinsic redundancy, distribution, and mobility. At the same time, the forwarding of navigation messages is the only form of cooperation that is required. This means that the robots are free in terms of their movement and location, and they can be involved in other tasks, unrelated to the navigation of the searching robot. This gives the system a high level of flexibility in terms of application scenarios, and a high degree of robustness with respect to robot failures or unexpected events. We study the algorithm in two different scenarios, both in simulation and on real robots. In the first scenario, a single searching robot needs to find a single target, while all other robots are involved in tasks of their own. In the second scenario, we study collective navigation: all robots of the swarm navigate back and forth between two targets, which is a typical scenario in swarm robotics. We show that in this case, the proposed algorithm gives rise to synergies in robot navigation, and it lets the swarm self-organize into a robust dynamic structure. The emergence of this structure improves navigation efficiency and lets the swarm find shortest paths.     

Localized low-level re-expression of high-affinity mesolimbic nicotinic acetylcholine receptors restores nicotine-induced locomotion but not place conditioning

High-affinity, β2-subunit-containing (β2*) nicotinic acetylcholine receptors (nAChRs) are essential for nicotine reinforcement; however, these nAChRs are found on both gamma-aminobutyric acid (GABA) and dopaminergic (DA) neurons in the ventral tegmental area (VTA) and also on terminals of glutamatergic and cholinergic neurons projecting from the pedunculopontine tegmental area and the laterodorsal tegmental nucleus. Thus, systemic nicotine administration stimulates many different neuronal subtypes in various brain nuclei. To identify neurons in which nAChRs must be expressed to mediate effects of systemic nicotine, we investigated responses in mice with low-level, localized expression of β2* nAChRs in the midbrain/VTA. Nicotine-induced GABA and DA release were partially rescued in striatal synaptosomes from transgenic mice compared with tissue from β2 knockout mice. Nicotine-induced locomotor activation, but not place preference, was rescued in mice with low-level VTA expression, suggesting that low-level expression of β2* nAChRs in DA neurons is not sufficient to support nicotine reward. In contrast to control mice, transgenic mice with low-level β2* nAChR expression in the VTA showed no increase in overall levels of cyclic AMP response element-binding protein (CREB) but did show an increase in CREB phosphorylation in response to exposure to a nicotine-paired chamber. Thus, CREB activation in the absence of regulation of total CREB levels during place preference testing was not sufficient to support nicotine place preference in β2 trangenic mice. This suggests that partial activation of high-affinity nAChRs in VTA might block the rewarding effects of nicotine, providing a potential mechanism for the ability of nicotinic partial agonists to aid in smoking cessation.