VARIABLE SELECTION ON EUROSTA'S GALL SIZE,I: THE EXTENT AND NATURE OF VARIATION IN PHENOTYPIC SELECTION

Natural fluctuations in environmental conditions are likely to induce variation in the intensity or direction of natural selection. A long-term study of the insect, Eurosta solidaginins Fitch (Diptera; Tephritidae), which induces stem galls on the perennial herb Solidago altissima (Asteraceae) was performed to explore the patterns of variation in phenotypic selection. The intensity of selection imposed by parasitoids and predators on gallmaking larvae, for gall size, was measured across 16 populations over the course of 4 generations, for a total of 64 population-generations. Directional selection was quantified by i, the selection intensity, and variance selection by j‘, a measure of the intensity of selection on phenotypic variance. Size-dependent attack by parasitoids caused upward directional selection (mean i_p = 0.42; SE = 0.023), while size-dependent bird attack favored larvae that induced smaller galls (mean i_b = -0.07; SE = 0.013. The mean net directional selection intensity was 0.35 (SE = 0.030), which indicates that insects inducing larger galls are generally favored by selection. The opposing patterns of size-dependent attack resulted in stabilizing selection in half the population generations, with an overall average. j‘ of -0.11 (SE = 0.078). The magnitude of directional selection was strongly influenced by the population mean gall size and weakly by the optimal gall size. The intensity of variance selection was strongly influenced by the shape of the fitness function, with sigmoidal and Gaussian-like shapes causing greater depletion of phenotypic variance.     

Inhibition of hepatic deiodination of thyroxine is caused by selenium deficiency in rats.

Selenium (Se) deficiency produced up to a 14-fold decrease in hepatic tri-iodothyronine (T3) production from thyroxine (T4) in vitro. The T3 production rate could not be restored by the addition of a variety of cofactors, nor by the addition of control homogenate. The impairment in hepatic T3 production observed in Se deficiency was reflected in the concentrations of thyroid hormones circulating in plasma, T4 being increased approx. 40% and T3 being decreased by 30%. However, the fall in plasma T3 concentrations was smaller than might be expected in view of the marked decreased in T3 production. Se deficiency had no measurable effect on plasma reverse-tri-iodothyronine concentrations. The data suggest that Se deficiency produces an inhibition of both 5- and 5'-deiodination, consistent with the widely held view that these reactions are catalysed by the same enzyme complex. The mechanism of inhibition appears not be mediated by changes in thiol levels, but a direct role of Se in the activity of the deiodinase complex cannot be excluded.     

Stereoselective formation of a 2′(3′)-aminoacyl ester of a nucleotide

Summary Reaction ofDl-serine and adenosine-5-phosphorimidazolide in the presence of adenosine-5-(O-methylphosphate) and imidazole resulted in the stereoselective synthesis of the aminoacyl nucleotide ester 2(3)-O-seryl-adenosine-5-(O-methylphosphate). The enantiomeric excess ofd-serine incorporated into 2(3)-O-seryl-adenosine-5-(O-methylphosphate) was about 9%. Adenylyl-(5N)-serine and an unknown product also incorporated an excess ofd-serine; however, serylserine showed an excess ofl-serine. The relationship of these results to the origin of the biological pairing ofl-amino acids and nucleotides containingd-ribose is discussed.     

Low-Level Microwave Irradiations Affect Central Cholinergic Activity in the Rat

Sodium-dependent high-affinity choline uptake was measured in various regions of the brains of rats irradiated for 45 min with either pulsed or continuous-wave low-level microwaves (2,450 MHz; power density, 1 mW/cm2; average whole-body specific absorption rate, 0.6 W/kg). Pulsed microwave irradiation (2-microseconds pulses, 500 pulses/s) decreased choline uptake in the hippocampus and frontal cortex but had no significant effect on the hypothalamus, striatum, and inferior colliculus. Pretreatment with a narcotic antagonist (naloxone or naltrexone; 1 mg/kg i.p.) blocked the effect of pulsed microwaves on hippocampal choline uptake but did not significantly alter the effect on the frontal cortex. Irradiation with continuous-wave microwaves did not significantly affect choline uptake in the hippocampus, striatum, and hypothalamus but decreased the uptake in the frontal cortex. The effect on the frontal cortex was not altered by pretreatment with narcotic antagonist. These data suggest that exposure to low-level pulsed or continuous-wave microwaves leads to changes in cholinergic functions in the brain.     

Characterization of specific fluorenylmethyloxycarbonyl-containing calmodulin adducts by spectroscopy and phosphodiesterase stimulation

A reagent (I, N⁴-(9-fluorenylmethyloxycarbonyl-4-amino-1-oxyl-4-succinimidyloxycarbonyl-2,2,6,6-tetramethylpiperidine)) that acylates calmodulin specifically at lysines 75 and 148 was recently described (Jackson and Puett, 1984). Chromatographic procedures are described that permit purification to apparent homogeneity of a 1 : 1 and a 2 : 1 adduct characterized by modification at just Lys 75 or at Lys 75 and Lys 148, respectively. These adducts are suitable for detailed characterization in an effort to provide information on calmodulin structure-function relationships. The adducts were incapable of, or exhibited low potency (e.g., 0.1% that of calmodulin) in, stimulating the activity of an activatable bovine brain cyclic nucleotide phosphodiesterase (3,5-cyclic AMP 5-nucleotidehydrolase, EC 3.1.4.17) preparation. Electron paramagnetic resonance (EPR) spectroscopy of the adducts yielded rotational correlation times of approximately 3–6 nsec, in agreement with the expected value for a hydrated protein of this molecular weight (5–7 nsec). Thus, the nitroxide reporter group appears to monitor closely the motion of the protein, and there is no evidence of a major conformational change in the derivative relative to calmodulin. Interestingly, removal of the fluorenylmethyloxycarbonyl portion from the 1 : 1 adduct to give a deprotected 1 : 1 adduct resulted in apparent greater mobility of the probe, since the rotational correlation coefficient was found to be 1 nsec. Circular dichroic spectra were obtained over the wavelength interval 200–250 nm on the two adducts and on the deprotected 1 : 1 adduct. These derivatives, like calmodulin, exhibited a Ca²⁺-mediated increase in helicity, and the spectra of the adducts in the presence of a chelating agent and in the presence of saturating Ca²⁺ were similar to those obtained for calmodulin. Thus, the adducts have secondary structures similar to the native protein. Proton nuclear magnetic resonance spectra were determined in the aromatic region (6–8 ppm) for the deprotected 1 : 1 adduct before and after reduction of the nitroxide with ascorbate. The nitroxide had little effect on the chemical shifts of the two tyrosines and the single histidine relative to calmodulin, although the histidine C4 resonance was markedly altered by the addition of ascorbate. In order to explore in greater detail the tertiary structure of the 1 : 1 adduct, a reagent similar to I, but not paramagnetic, was synthesized. This compound II, -N-(9-fluorenylmethyloxycarbonyl)alanine N-hydroxysuccinimide ester, like I, forms a 1 : 1 adduct at Lys 75 and a 2 : 1 adduct at Lys 75 and Lys 148. Proton NMR spectra of adducts with II were not complicated by the relaxation effects arising from adducts with I; thus more definitive assignments could be made to the upfield resonances, including the fluorene protons. Again, it was possible to conclude that adduct formation had no major effect on the tertiary structure of the protein as monitored by chemical shifts associated with various residues. We conclude that modification of just Lys 75, a residue in the long connecting helix of calmodulin, does not lead to major changes in protein conformation but does interfere with the ability of calmodulin to stimulate an activatable form of bovine brain cyclic nucleotide phosphodiesterase.