Highland forest’s environmental complexity drives landscape genomics and connectivity of the rodent Peromyscus melanotis

Landscape Ecology - Deciphering how the complex environmental dynamics of highland temperate forests drive local patterns of genetic variation is key to understanding species diversity and...     

Simulation of cow-calf production with and without realistic levels of variability

The Colorado beef cattle production model, a whole-herd, individual-animal, life-cycle simulation model, was used to determine if level of simulated variability affects simulation results. Beyond variability created by deterministic equations describing known biological relationships and direct input, the Colorado beef cattle production model can produce additional variation in a number of traits through its capacity to generate multinormal deviates for each animal. Runs simulating cow-calf production under ample and sparse levels of nutrition were performed with less than realistic and realistic levels of variability for mature weight, milk production, gestation length, maintenance requirements, appetite, and combinations thereof. Under poor nutrition, simulation with less than realistic variability altered means for pregnancy rate, postpartum interval, milk production, weaning weight, and mature weight by up to 14%, 8.6 d, 0.8 kg/d, 9.6 kg, and 19.1 kg, respectively, in addition to changing the output for numerous other variables. The level of simulated variability affected the means of output variables through 2 mechanisms: (1) change in potentials due to differential culling, which can only take place if potentials are allowed to vary; and (2) further interaction with the model's nonlinear, deterministic equations. Our findings indicate that by not simulating realistic levels of variability, models with nonlinear functions may yield misleading results.     

Biomass of Tomato Seedlings Exposed to an Allelopathic Phenolic Acid and Enriched Atmospheric Carbon Dioxide

Increased atmospheric CO₂ can affect plant growth, so competition among plants may be influenced. Allelopathy is one mechanism involved in plant competition. Experiments were conducted in a controlled-environment chamber to determine if the concentration of atmospheric CO₂ altered the dose-response relationship between an allelopathic phenolic acid and tomato seedling biomass. Seeds of Lycopersicon lycopersicum were planted in quartz sand in styrofoam cups and allowed to germinate and grow for 15–17 days. During the next 14 days, seedlings were watered twice daily with nutrient solution amended with p-coumaric acid (4-hydroxycinnamic acid, HOC₆H₄CH = CHCO₂H; ranging 0–0.85 mg mL^-1; 5 concentrations in each experiment) and exposed 24 hr day^-1 in continuous-stirred tank reactors (CSTRs) to ambient air (335–375 ppm CO₂) or ambient air to which 350 ppm CO₂ was added (i.e., approximately twice-ambient CO₂; two CSTRs per CO₂ concentration in each experiment). Dose-response data relating p-coumaric acid concentration and shoot, root, and total biomass were fit to a flexible decay function. In all three experiments, twice-ambient CO₂ significantly increased the y-intercept for the dose-response model for the p-coumaric acid effect on shoot biomass by 25–50% but had negligible effects on other aspects of the models. Results suggest that if CO₂ affects plant competition, mechanisms involving allelopathic phenolic acids may not be involved.     

Ergovaline-induced vasoconstriction in an isolated bovine lateral saphenous vein bioassay

Ergovaline has been proposed as a toxic component of endophyte-infected tall fescue. As many of the symptoms of fescue toxicosis are a result of compromised circulation, the objective of this study was to examine the vasoconstrictive potentials of ergovaline and a more documented ergopeptine, ergotamine, using a bovine, lateral (cranial branch) saphenous vein bioassay. Segments of the cranial branch of the lateral saphenous vein (2 to 3 cm) were collected from healthy, mixed breed cattle (n = 12 and n = 5 for the ergovaline and ergotamine experiments, respectively) at local abattoirs. The veins were trimmed of excess fat and connective tissue, sliced into 2- to 3-mm cross sections, and suspended in a myograph chamber containing 5 mL of a modified Krebs-Henseleit, oxygenated buffer (95% O2 + 5% CO2; pH = 7.4; 37 degrees C). The tissue was allowed to equilibrate at 1 g of tension for 90 min before of the addition of treatments. Increasing doses of ergovaline (1x10(-11) to 1 x10(-4) M) or ergotamine (1 x10(-11) to 1 x 10(-5) M) were administered every 15 min after buffer replacement. Contractile response data were normalized to a percentage induced by a reference dose of norepinephrine (1 x10(-4) M). Contractile responses of saphenous veins were similar for ergovaline and ergotamine. Initial contractile responses began at 1 x10(-8) M for both ergovaline and ergotamine (4.4 +/- 0.8% and 5.6 +/-1.1%, respectively). Vascular tension continued to increase as the alkaloid concentrations increased (maximums: 43.7 +/-7.1% at 1 x10(-5) M ergotamine; 69.6 +/- 5.3% at 1 x10(-4) M ergovaline). Interestingly, ergovaline-induced contractions (1 x10(-4) M) were not reversed by repeated buffer replacement over a 105-min period. As previously shown with ergotamine, these results confirm that ergovaline is a potent vasoconstrictor. The resistance of an ergovaline-induced contraction to relaxation over an extended period of time suggests a potential for bioaccumulation of this ergopeptine alkaloid and may aid in understanding its toxicity within the animal.     

COMPARISON OF CARDIOPULMONARY RESPONSES TO DETOMIDINE ADMINISTERED AS AN INTRAVENOUS STEADY-STATE INFUSION VS INTRAVENOUS BOLUS IN STANDING HORSES

We compared the cardiopulmonary response to detomidine (DET) administered to two different groups of horses after IV steady-state infusion (n = 7) or IV bolus (n = 6) at similar plasma DET concentrations. Based upon previously reported kinetics, a computer predicted DET plasma concentrations and controlled an infusion pump which maintained steady-state arterial plasma DET for the infusion studies. These pharmacokinetics were used to estimate DET plasma concentrations at measurement times following IV bolus DET in the second group of horses. Cardiopulmonary measurements were made following 15 minutes of steady-state infusion and 30 minutes after IV bolus of DET. DET plasma concentration was estimated to be similar between A), 19 ng DET/ml plasma infusion and 30 minutes following an IV bolus dose of 10 γg DET/kg, (estimated plasma concentration 20.5 ng/ml), and B), 43 ng DET/ml plasma infusion and 30 minutes following an IV bolus of 20 γg DET/kg (estimated plasma concentration 42 ng/ml).     

State-to-State Rates for the D + H2(v = 1, j = 1) rarr HD(v', j') + H Reaction: Predictions and Measurements

A fully quantal wavepacket approach to reactive scattering in which the best available H(3) potential energy surface was used enabled a comparison with experimentally determined rates for the D + H(2)(v = 1, j = 1) --> HD(v' = 0, 1, 2; j') + H reaction at significantly higher total energies (1.4 to 2.25 electron volts) than previously possible. The theoretical results are obtained over a sufficient range of conditions that a detailed simulation of the experiment was possible, thus making this a definitive comparison of experiment and theory. Good to excellent agreement is found for the vibrational branching ratios and for the rotational distributions within each product vibrational level. However, the calculated rotational distributions are slightly hotter than the experimentally measured ones. This small discrepancy is more marked for products for which a larger fraction of the total energy appears in translation. The most likely explanation for this behavior is that refinements are needed in the potential energy surface.