Similar Differences In Rates Research Articles

EVOLUTIONARY RATES IN THE ADAPTIVE RADIATION OF BEETLES ON PLANTS

Herbivorous insects and other small consumers are often specialized both in use of particular host taxa and in use of particular host tissues. Such consumers also often seem to show consistent differences in the rates of evolution of these two dimensions of host use, implying common processes, but this has been little studied. Here we quantify these rates of change in host use evolution in a major radiation of herbivorous insects, the Chrysomeloidea, whose diversity has been attributed to their use of flowering plants. We find a significant difference in the rates of evolutionary change in these two dimensions of host use, with host taxon associations most labile. There are apparently similar differences in rates of host use evolution in other parasite groups, suggesting the generality of this pattern. Divergences in parasite form associated with use of different host tissues may facilitate resource partitioning among successive adaptive radiations on particular host taxa.

EVOLUTIONARY RATES IN THE ADAPTIVE RADIATION OF BEETLES ON PLANTS*

Herbivorous insects and other small consumers are often specialized both in use of particular host taxa and in use of particular host tissues. Such consumers also often seem to show consistent differences in the rates of evolution of these two dimensions of host use, implying common processes, but this has been little studied. Here we quantify these rates of change in host use evolution in a major radiation of herbivorous insects, the Chrysomeloidea, whose diversity has been attributed to their use of flowering plants. We find a significant difference in the rates of evolutionary change in these two dimensions of host use, with host taxon associations most labile. There are apparently similar differences in rates of host use evolution in other parasite groups, suggesting the generality of this pattern. Divergences in parasite form associated with use of different host tissues may facilitate resource partitioning among successive adaptive radiations on particular host taxa.

Hypophysectomy does not alter the acinar zonation of gluconeogenesis or the mitochondrial redox state in rat liver.

The biochemical and functional heterogeneity of hepatocytes in different zones of the liver acinus may be related to the concentrations of hormones within the liver acinus. We examined the effects of hypophysectomy, which causes marked changes in plasma hormone levels and in activities of hepatic enzymes that are normally heterogeneously distributed, on the degree of metabolic zonation within the liver acinus. In hypophysectomized rats the activity of alanine aminotransferase was increased, but its normal zonation (predominance in the periportal zone) was preserved. The activity in cultured periportal and perivenous hepatocytes was increased by dexamethasone, but not by glucagon. Periportal hepatocytes from hypophysectomized rats expressed higher rates of gluconeogenesis in culture than did perivenous hepatocytes, irrespective of the absence or presence of dexamethasone, glucagon or insulin. Similar differences in rates of ketogenesis and in the mitochondrial redox state in response to glucagon were observed between periportal and perivenous hepatocytes from hypophysectomized rats as between cell populations from normal rats. Although hypophysectomy causes marked changes in hepatic enzyme activities, it does not alter the degree of zonation of alanine aminotransferase, gluconeogenesis or the mitochondrial redox state within the liver acinus.

26-hydroxylation of 5 beta-cholestane-3 alpha,7 alpha,12 alpha-triol by isolated nonparenchymal cells and hepatocytes from rat liver

The ability of isolated nonparenchymal and parenchymal rat liver cells to metabolize 5beta-cholestane-3alpha,7alpha,12alpha-triol and other bile acid intermediates has been investigated. Incubation of nonparenchymal cells with 5beta-cholestane-3alpha,7alpha,12alpha-triol resulted in the formation of one more polar product identified as 5beta-cholestane-3alpha,7alpha,12alpha,26-tetrol. The formation was linear with time up to 2 hr and with the number of cells, and showed saturation kinetics with respect to substrate concentration. The maximum rate of conversion was 90 pmol/10(6) cells per hr. Incubation of hepatocytes with the triol resulted in the formation of several more polar products. In addition to 5beta-cholestane-3alpha,7alpha,12alpha,26-tetrol, products with retention time on high pressure liquid chromatography identical with 3alpha,7alpha,12alpha-trihydroxy-5beta-cholestan-26-oic acid and cholic acid were observed. The identity of these products was verified by combined gas-liquid chromatography-mass spectrometry. The rate of conversion was linear with time for about 10 min and saturation with respect to substrate concentration was not attained. At identical substrate concentrations, the total rate of conversion (12.5 nmol/10(6) cells per hr) was at least two orders of magnitude higher than with the nonparenchymal cells. Similar differences in rates of conversion were observed with other C(27)-bile acid intermediates. It is concluded that the nonparenchymal cells do not play any significant role in the conversion of bile acid intermediates, either under physiological conditions or under experimental conditions where such steroids have been administered intravenously.-Dueland, S., J. I. Pedersen, C. A. Drevon, and I. Björkhem. 26-Hydroxylation of 5beta-cholestane-3alpha,7alpha,12alpha-triol by isolated nonparenchymal cells and hepatocytes from rat liver.