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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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Vertical profiles were measured in soil cores taken from flooded rice fields in the Po valley during July and August 1990.
Methane concentrations generally increased with depth and reached maximum values of 150–500 μM in 5–13 cm depth. However,
the shape of the profiles was very different when studying different soil cores. The CH4 content of gas bubbles showed a similar variability which apparently was due to spatial rather than temporal inhomogeneities.
Similar inhomogeneities were observed in the vertical profiles of acetate, propionate, lactate, and formate which showed maximum
values of 1500, 66, 135, and 153, μM, respectively. However, maxima and minima of the vertical profiles of the different substates
usually coincided in one particular soil core. Large inhomogeneities in the vertical profiles were also observed for the rates
of total CH4 production, however, the percentage contribution of H2/CO2 to CH4 production was relatively homogeneous at 24 ± 7% (SD). Similarly, the H2 content of gas bubbles was relatively constant at 93.3 ± 9.6 ppmv when randomly sampled in the rice field at different times
of the day. A small contribution (6%) of H2/CO2 to acetate production was also observed. Vertical profiles of the respiratory index (RI) for [2-14C] acetate showed that acetate was predominantly degraded by methanogenesis in 5–11 cm depth, but by respiration in the surface
soil (3 cm depth) and in soil layers below 13–16 cm depth which coincided with a transition of the colour (grey to reddish)
and the physical characteristics (porosity, density) of the soil. The observations indicate that the microbial community which
degrades organic matter to CH4 is in itself relatively homogenous, but operates at highly variable rates within the soil structure.
Author for correspondence 相似文献
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