Territoriality and population regulation in juvenile salmonids

Territorial behaviour is thought to play a role in limiting population density. Consequently the factors that affect territory size would also influence population density. I examined the relationship between visibility and territory size in young-of-the year (YOY) rainbow trout ( Oncorhynchus mykiss ) to test the hypothesis that increasing habitat heterogeneity results in a reduction in territory size and consequently in higher population density. As predicted, the territory size decreased with decreasing visibility. However, the decrease in territory size did not produce an increase in density, perhaps because few individuals defended territories or because the experiment was too short for population density to reach an equilibrium. The optimal size of a contiguous territory is predicted (1) to remain unchanged at low food abundance levels and (2) to decrease only when food abundance is high enough to reduce territory size below the contiguous optimum. I manipulated food abundance to test this model, using YOY steelhead trout ( Oncorhynchus mykiss ). Increasing competition resulted in increasing mortality, higher propensity to emigrate, higher variance in body mass, lower growth, lower population density, lower biomass and lower percent habitat saturation. Territory size did not change with food abundance. Increasing levels of intraspecific competition in stream-dwelling salmonid populations often lead to density dependent mortality and emigration. However, density dependent growth is less frequently detected. I examined the relationship between average fork length and density of YOY Atlantic salmon ( Salmo salar ), to investigate (1) whether there is evidence for density dependent growth, (2) the shape of the relationship, and (3) the effect of spatial and temporal scale on the ability to detect density dependent growth. There was a negative relationship, described by a power curve, between the average body size and density of YOY Atlantic salmon. Most of the variation in body size was explained by YOY density, with year, location and older salmon density accounting for a minor proportion of the variation. Density dependent growth was equally well detected within and across years. Spatial scale did not affect the ability to detect density dependent growth. My analysis suggested that YOY Atlantic salmon populations are regulated by two different mechanisms: density dependent growth at low densities and density dependent mortality at high densities

The effect of visual isolation on territory size and population density of juvenile rainbow trout (Oncorhynchus mykiss)

Visibility is thought to affect the territory size of visually oriented animals but there have been few experimental tests of the hypothesis. We re-examined the relationship between visibility and territory size in juvenile salmonids to test the hypothesis that increasing habitat heterogeneity results in a reduction in territory size and consequently in higher population densities. Equal densities of young-of-the-year rainbow trout (Oncorhynchus mykiss) were stocked in two experimental treatments with low visibility and a control treatment with high visibility. Visibility was decreased by placing large stones or plywood dividers onto the substrate of experimental stream channels. As predicted, the size of individual territories decreased with decreasing visibility of the habitat. However, the treatments did not differ significantly in population density or growth rate of the fish. While this study confirms the inverse relationship between habitat visibility and territory size, the decrease in territory size did not produce an increase in population density of juvenile salmonids

The Effect of Newly Developed OPLS-AA Alanyl Radical Parameters on Peptide Secondary Structure

Recent studies using ab initio calculations have shown that C_α-centered radical formation by H-abstraction from the backbone of peptide residues has dramatic effects on peptide structure and have suggested that this reaction may contribute to the protein misfolding observed in Alzheimer’s and Parkinson’s diseases. To enable the effects of C_α-centered radicals to be studied in longer peptides and proteins over longer time intervals, force-field parameters for the C_α-centered Ala radical were developed for use with the OPLS force field by minimizing the sum of squares deviation between the quantum chemical and OPLS-AA energy hypersurfaces. These parameters were used to determine the effect of the C_α-centered Ala radical on the structure of a hepta-alanyl peptide in molecular dynamics (MD) simulations. A negligible sum-of-squares energy deviation was observed in the stretching parameters, and the newly developed OPLS-AA torsional parameters showed a good agreement with the LMP2/cc-pVTZ­(-f) hypersurface. The parametrization also demonstrated that derived force-field bond length and bond angle parameters can deviate from the quantum chemical equilibrium values, and that the improper torsional parameters should be developed explicitly with respect to the coupled torsional parameters. The MD simulations showed planar conformations of the C_α-containing residue (Alr) are preferred and these conformations increase the formation of γ-, α-, and π-turn structures depending on the position in the turn occupied by the Alr residue. Higher-ordered structures are destabilized by Alr except when this residue occupies position “i + 1” of the 3₁₀-helix. These results offer new insight into the protein-misfolding mechanisms initiated by H-abstraction from the C_α of peptide and protein residues

Spherical LDH–Ag°-Montmorillonite Heterocoagulated System with a pH-Dependent Sol–Gel Structure for Controlled Accessibility of AgNPs Immobilized on the Clay Lamellae

Aqueous suspensions of spherical ZnMgAl-layered double hydroxides [LDH­(sph)] and antibacterial silver nanoparticles (AgNPs) deposited on the lamellae of montmorillonite were used for the synthesis of composites, which behave like coherent gels at low pH (≲4.5) and incoherent sols at higher pH (≳4.5). The composition of the composite was chosen as LDH­(sph)/Ag°-montm. = 25:75 wt % in order to ensure a sol–gel transition that can also be characterized by viscometry. This pH-sensitive heterocoagulated system consisting of oppositely charged colloid particles was suitable for the release of antimicrobial AgNPs immobilized on the clay lamellae via a pH-controlled gel–sol transition. The heterocoagulation process was also characterized by surface charge titration measurements. Spherical LDH/Ag°-montmorillonite composite samples were identified by X-ray diffraction (XRD) measurements. The morphological properties of the composites were studied, and the presence of the heterocoagulated structure was confirmed by scanning electron microscopy (SEM). The nanoscale structure of the LDH­(sph)–Ag°-montmorillonite composite obtained was also verified by small-angle X-ray scattering (SAXS), and the rheological characteristics were studied at various pH values. The viscosity and yield value of the composite decreased by an order of magnitude upon increasing the pH from 3.0 to 5.5. The sol–gel transition of the composite suspension was reversible in the previously mentioned pH range

[Tl^III(dota)]⁻: An Extraordinarily Robust Macrocyclic Complex

The X-ray structure of {C­(NH₂)₃}­[Tl­(dota)]·H₂O shows that the Tl³⁺ ion is deeply buried in the macrocyclic cavity of the dota^4– ligand (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetate) with average Tl–N and Tl–O distances of 2.464 and 2.365 Å, respectively. The metal ion is directly coordinated to the eight donor atoms of the ligand, which results in a twisted square antiprismatic (TSAP′) coordination around Tl³⁺. A multinuclear ¹H, ¹³C, and ²⁰⁵Tl NMR study combined with DFT calculations confirmed the TSAP′ structure of the complex in aqueous solution, which exists as the Λ­(λλλλ)/Δ­(δδδδ) enantiomeric pair. ²⁰⁵Tl NMR spectroscopy allowed the protonation constant associated with the protonation of the complex according to [Tl­(dota)]⁻ + H⁺ ⇆ [Tl­(Hdota)] to be determined, which turned out to be p<i>K</i>^H_Tl(dota) = 1.4 ± 0.1. [Tl­(dota)]⁻ does not react with Br^–, even when using an excess of the anion, but it forms a weak mixed complex with cyanide, [Tl­(dota)]⁻ + CN^– ⇆ [Tl­(dota)­(CN)]^2–, with an equilibrium constant of <i>K</i>_mix = 6.0 ± 0.8. The dissociation of the [Tl­(dota)]⁻ complex was determined by UV–vis spectrophotometry under acidic conditions using a large excess of Br^–, and it was found to follow proton-assisted kinetics and to take place very slowly (∼10 days), even in 1 M HClO₄, with the estimated half-life of the process being in the 10⁹ h range at neutral pH. The solution dynamics of [Tl­(dota)]⁻ were investigated using ¹³C NMR spectroscopy and DFT calculations. The ¹³C NMR spectra recorded at low temperature (272 K) point to <i>C</i>₄ symmetry of the complex in solution, which averages to <i>C</i>_4<i>v</i> as the temperature increases. This dynamic behavior was attributed to the Λ­(λλλλ) ↔ Δ­(δδδδ) enantiomerization process, which involves both the inversion of the macrocyclic unit and the rotation of the pendant arms. According to our calculations, the arm-rotation process limits the Λ­(λλλλ) ↔ Δ­(δδδδ) interconversion

Novel-Type GABA_B PAMs: Structure–Activity Relationship in Light of the Protein Structure

Selecting a known HTS hit with the pyrazolo[1,5-a]pyrimidine core, our project was started from CMPPE, and its optimization was driven by a ligand-based pharmacophore model developed on the basis of published GABAB positive allosteric modulators (PAMs). Our primary goal was to improve the potency by finding new enthalpic interactions. Therefore, we included the lipophilic ligand efficiency (LLE or LipE) as an objective function in the optimization that led to a carboxylic acid derivative (34). This lead candidate offers the possibility to improve potency without drastically inflating the physicochemical properties. Although the discovery of the novel carboxyl feature was surprising, it turned out to be an important element of the GABAB PAM pharmacophore that can be perfectly explained based on the new protein structures. Rationalizing the binding mode of 34, we analyzed the intersubunit PAM binding site of GABAB receptor using the publicly available experimental structures

Dithallium(III)-Containing 30-Tungsto-4-phosphate, [Tl₂Na₂(H₂O)₂(P₂W₁₅O₅₆)₂]^16–: Synthesis, Structural Characterization, and Biological Studies

Here we report on the synthesis and structural characterization of the dithallium­(III)-containing 30-tungsto<i>-</i>4-phosphate [Tl₂Na₂(H₂O)₂­{P₂W₁₅O₅₆}₂]^16– (<b>1</b>) by a multitude of solid-state and solution techniques. Polyanion <b>1</b> comprises two octahedrally coordinated Tl³⁺ ions sandwiched between two trilacunary {P₂W₁₅} Wells–Dawson fragments and represents only the second structurally characterized, discrete thallium-containing polyoxometalate to date. The two outer positions of the central rhombus are occupied by sodium ions. The title polyanion is solution-stable as shown by ³¹P and ^203/205Tl NMR. This was also supported by Tl NMR spectra simulations including several spin systems of isotopologues with half-spin nuclei (²⁰³Tl, ²⁰⁵Tl, ³¹P, ¹⁸³W). ²³Na NMR showed a time-averaged signal of the Na⁺ counter cations and the structurally bonded Na⁺ ions. ^203/205Tl NMR spectra also showed a minor signal tentatively attributed to the trithallium-containing derivative [Tl₃Na­(H₂O)₂­(P₂W₁₅O₅₆)₂]^14–, which could also be identified in the solid state by single-crystal X-ray diffraction. The bioactivity of polyanion <b>1</b> was also tested against bacteria and <i>Leishmania</i>