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1.
The tolerance of low oxygen stress in insecticide-resistant and susceptible populations of mosquitofish () was investigated. Dissolved oxygen was reduced chemically with formaldehyde and sodium sulfite treatment. Available oxygen was reduced physically through barriers, both by preventing oxygen exchange at the air-water interface and by preventing the fish from contacting the surface of the water. In all cases, the tolerance to low oxygen stress was reduced in the insecticide-resistant population compared to the susceptible population. The results indicate that although tolerance of pesticides in the resistant population has been dramatically increased by environmental selective pressures, tolerance to other stresses has not been concomitantly increased. 相似文献
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The effect of prior hypophysectomy upon mirex-induced liver hypertrophy in male Sprague-Dawley rats was examined. Mirex had no effect upon adrenal weight, liver weight, plasma glucose or plasma corticosterone in hypophysectomized rats. However, daily corticosterone supplements (20 mg/kg body weight, sc) given to mirex-treated hypophysectomized animals yielded a 52% increase in liver weight to body weight ratios over those observed in mirex-treated hypophysectomized animals not receiving supplement. In intact rats, both liver weight to body weight ratios and plasma ACTH were significantly increased over controls 2 days after mirex treatment. These results indicate that mirex-induced liver enlargement not only requires corticosterone, but that the response is dependent upon an intact pituitary-adrenalcortical axis. 相似文献
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The phylogeny of Greya Busck (Lepidoptera: Prodoxidae) was inferred from
nucleotide sequence variation across a 765-bp region in the cytochrome
oxidase I and II genes of the mitochondrial genome. Most parsimonious
relationships of 25 haplotypes from 16 Greya species and two outgroup
genera (Tetragma and Prodoxus) showed substantial congruence with the
species relationships indicated by morphological variation. Differences
between mitochondrial and morphological trees were found primarily in the
positions of two species, G. variabilis and G. pectinifera, and in the
branching order of the three major species groups in the genus. Conflicts
between the data sets were examined by comparing levels of homoplasy in
characters supporting alternative hypotheses. The phylogeny of Greya
species suggests that host-plant association at the family level and larval
feeding mode are conservative characters. Transition/transversion ratios
estimated by reconstruction of nucleotide substitutions on the phylogeny
had a range of 2.0-9.3, when different subsets of the phylogeny were used.
The decline of this ratio with the increase in maximum sequence divergence
among taxa indicates that transitions are masked by transversions along
deeper internodes or long branches of the phylogeny. Among transitions,
substitutions of A-->G and T-->C outnumbered their reciprocal
substitutions by 2-6 times, presumably because of the approximately 4:1
(77%) A+T-bias in nucleotide base composition. Of all transversions,
73%-80% were A<-->T substitutions, 85% of which occurred at third
positions of codons; these estimates did not decrease with an increase in
maximum sequence divergence of taxa included in the analysis. The high
frequency of A<-->T substitutions is either a reflection or an
explanation of the 92% A+T bias at third codon positions.
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