Logistic population growth under random dispersal

Various diffusion processes employed for modelling logistic growth are briefly summarized. A discrete-time, discrete-state space stochastic process for population growth is proposed and analyzed with either Bose-Einstein or Maxwell-Boltzmann statistics for the distribution of offspring in available sites in a restricted region. A diffusion approximation is constructed, which differs from those previously employed. The logistic law is a natural deterministic analog of the diffusion process.     

Developmental progression of myosin gene expression in cultured muscle cells

Myosin heavy chains are encoded by distinct members of a multigene family at different stages of muscle development. Study of the underlying regulatory mechanisms has been hindered because transitions in myosin expression have not been readily attained in tissue culture. Here we show a transition from early (fetal) to late (perinatal/adult) myosins defined by two monoclonal antibodies, F1.652 and N3.36, in the myotubes of mouse C2C12 cells. On day 1 of differentiation, essentially all myosin was early myosin. By day 8, early myosin dropped to 25% of its day 1 value and was replaced by late myosin. The transition occurred without neural contact, connective tissue components, or complex substrates, suggesting that its regulation may be intrinsic to the muscle cell. Our results demonstrate that a developmental progression in myosin gene expression, which occurs rapidly, with high frequency, and under relatively simple conditions, is now amenable to molecular analysis in cultured muscle cells.     

Serotonin receptor expression in human prefrontal cortex: balancing excitation and inhibition across postnatal development

Serotonin and its receptors (HTRs) play critical roles in brain development and in the regulation of cognition, mood, and anxiety. HTRs are highly expressed in human prefrontal cortex and exert control over prefrontal excitability. The serotonin system is a key treatment target for several psychiatric disorders; however, the effectiveness of these drugs varies according to age. Despite strong evidence for developmental changes in prefrontal Htrs of rodents, the developmental regulation of HTR expression in human prefrontal cortex has not been examined. Using postmortem human prefrontal brain tissue from across postnatal life, we investigated the expression of key serotonin receptors with distinct inhibitory (HTR1A, HTR5A) and excitatory (HTR2A, HTR2C, HTR4, HTR6) effects on cortical neurons, including two receptors which appear to be expressed to a greater degree in inhibitory interneurons of cerebral cortex (HTR2C, HTR6). We found distinct developmental patterns of expression for each of these six HTRs, with profound changes in expression occurring early in postnatal development and also into adulthood. However, a collective look at these HTRs in terms of their likely neurophysiological effects and major cellular localization leads to a model that suggests developmental changes in expression of these individual HTRs may not perturb an overall balance between inhibitory and excitatory effects. Examining and understanding the healthy balance is critical to appreciate how abnormal expression of an individual HTR may create a window of vulnerability for the emergence of psychiatric illness.     

Host diversity and behavior determine patterns of interspecies transmission and geographic diffusion of avian influenza A subtypes among North American wild reservoir species

Wild birds can carry avian influenza viruses (AIV), including those with pandemic or panzootic potential, long distances. Even though AIV has a broad host range, few studies account for host diversity when estimating AIV spread. We analyzed AIV genomic sequences from North American wild birds, including 303 newly sequenced isolates, to estimate interspecies and geographic viral transition patterns among multiple co-circulating subtypes. Our results show high transition rates within Anseriformes and Charadriiformes, but limited transitions between these orders. Patterns of transition between species were positively associated with breeding habitat range overlap, and negatively associated with host genetic distance. Distance between regions (negative correlation) and summer temperature at origin (positive correlation) were strong predictors of transition between locations. Taken together, this study demonstrates that host diversity and ecology can determine evolutionary processes that underlie AIV natural history and spread. Understanding these processes can provide important insights for effective control of AIV.     

Environmental variables affecting small-scale distributions of five rotifer species in Lancaster Lake,Michigan

The small-scale distributions of the rotifers Polyarthra vulgaris, Synchaeta stylata, Conochilus unicornis, Hexarthra mira, and Asplanchna priodonta were investigated in Lancaster Lake, Cheboygan County, Michigan, July 21, 1974. Measurements were taken for 13 depths (at 1-m intervals) and at 4 times of the day (1:00 AM, 7:00 AM, 1:00 PM, and 7:00 PM). In addition, the abundances of 6 crustacean, 2 planktonic dipteran, and 10 algal species, as well as temperature, light, oxygen, chlorophyll a, alkalinity, pH and free carbon dioxide were measured. Whereas abiotic factors appeared to control large scale occupation of the lake, and excluded most species from the deeper portions of the hypolimnion, small-scale distributional variation of the rotifers depended upon biotic interactions, particularly with the crustacean zooplankton.     

Curium(III) complexation with pyoverdins secreted by a groundwater strain of Pseudomonas fluorescens

Pyoverdins, bacterial siderophores produced by ubiquitous fluorescent Pseudomonas species, have great potential to bind and thus transport actinides in the environment. Therefore, the influence of pyoverdins secreted by microbes on the migration processes of actinides must be taken into account in strategies for the risk assessment of potential nuclear waste disposal sites. The unknown interaction between curium(III) and the pyoverdins released by Pseudomonas fluorescens (CCUG 32456) isolated from the granitic rock aquifers at the Äspö Hard Rock Laboratory (Äspö HRL), Sweden, is the subject of this paper. The interaction between soluble species of curium(III) and pyoverdins was studied at trace curium(III) concentrations (3 × 10^?7 M) using time-resolved laser-induced fluorescence spectroscopy (TRLFS). Three Cm³⁺—P. fluorescens (CCUG 32456) pyoverdin species, M_pH_qL_r, could be identified from the fluorescence emission spectra, CmH₂L⁺, CmHL, and CmL^?, having peak maxima at 601, 607, and 611 nm, respectively. The large formation constants, log β₁₂₁ = 32.50 ± 0.06, log β₁₁₁ = 27.40 ± 0.11, and log β₁₀₁ = 19.30 ± 0.17, compared to those of other chelating agents illustrate the unique complexation properties of pyoverdin-type siderophores. An indirect excitation mechanism for the curium(III) fluorescence was observed in the presence of the pyoverdin molecules.