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SONG Weibo Alan WARREN David ROBERTS SHANG Huimin Norbert WILBERT MIAO Miao YI Zhenzhen 《自然科学进展(英文版)》2005,15(8):700-707
The divisional process and systematic position of the marine scuticociliate Dexiotrichides pangi are studied. Based on both stomatogenetic data and 18S rDNA gene sequences, the phylogeny and morphogenetic characteristics of this taxon, and of other related genera, are analyzed and discussed. Both the divisionary events and the molecular biological data indicate that this speciesgenus, together with certain other genera in the Dexiotricha-complex, occupies an intermediate position between the tetrahymenids and the “typical” scuticociliate, which suggests that the Dexiotricha-like taxa should be excluded from the “true” scuticociliates. As a further contribution, the process of stomatogenesis in D. pangi can be summarized as follows: (1) The oral primordia in the opisthe are formed only by the proliferation of basal bodies in the scutica field, which subsequently develop into three membranelles, while the new paroral membrane seems to be generated by the sub-anterior portion of somatic kinety 1 (the 1st postoral intercalary kinety). The latter character exhibits a mode similar to Tetrahymena. (2) In the proter the parental membranelles are retained and remain unchanged throughout the entire division process; only the old paroral membrane is disassembled and differentiated into the anlage, which then gives rise to the new paroral membrane and the scutica of the proter. The 18S rRNA gene sequence reported here is the first one for a ciliate in the Dexiotricha-complex. 相似文献
146.
HUANG Zhiqun XU Zhihong BOYD Sue WILLIAMS David 《科学通报(英文版)》2005,50(22):2581-2586
Decomposition of stumps in successive rotation of Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) plantations was studied using a chronosequenee approach. The results showed that decomposition rate constant of Chinese fir stump was 0.02695 as calculated from Olson's model. The N content of stump increased during the first two-year decomposition. When the dead stump C/N ratio was 463.2 ± 27.3, the stumps started to release N. The pattern of P release was similar to that for N. However, K content of stumps showed a consistent declining trend over time during the whole decomposition. ^13C nuclear magnetic resonance spectroscopy with cross polarization and magic-angle spinning (^13C CPMAS-NMR) was used to analyse organic carbon (C) components in decomposing stumps. The ^13C CPMAS-NMR spectra of stumps displayed that stump was dominated by cellulose and hemieellulose. The spectra also showed the accumulation of intensity in alkyl C, aromatic C, and earboxyl C spectral regions, which was expected as the labile cellulose and hemieellulose components in O-alkyl C spectral region were selectively decomposed first. 相似文献
147.
Spectral analysis of phylogenetic data 总被引:12,自引:0,他引:12
The spectral analysis of sequence and distance data is a new approach to phylogenetic analysis. For two-state character sequences,
the character values at a given site split the set of taxa into two subsets, a bipartition of the taxa set. The vector which
counts the relative numbers of each of these bipartitions over all sites is called a sequence spectrum. Applying a transformation
called a Hadamard conjugation, the sequence spectrum is transformed to the conjugate spectrum. This conjugation corrects for
unobserved changes in the data, independently from the choice of phylogenetic tree. For any given phylogenetic tree with edge
weights (probabilities of state change), we define a corresponding tree spectrum. The selection of a weighted phylogenetic
tree from the given sequence data is made by matching the conjugate spectrum with a tree spectrum. We develop an optimality
selection procedure using a least squares best fit, to find the phylogenetic tree whose tree spectrum most closely matches
the conjugate spectrum. An inferred sequence spectrum can be derived from the selected tree spectrum using the inverse Hadamard
conjugation to allow a comparison with the original sequence spectrum.
A possible adaptation for the analysis of four-state character sequences with unequal frequencies is considered. A corresponding
spectral analysis for distance data is also introduced. These analyses are illustrated with biological examples for both distance
and sequence data. Spectral analysis using the Fast Hadamard transform allows optimal trees to be found for at least 20 taxa
and perhaps for up to 30 taxa.
The development presented here is self contained, although some mathematical proofs available elsewhere have been omitted.
The analysis of sequence data is based on methods reported earlier, but the terminology and the application to distance data
are new. 相似文献
148.
A sound, depending on the position of its source, can take more time to reach one ear than the other. This interaural (between the ears) time difference (ITD) provides a major cue for determining the source location. Many auditory neurons are sensitive to ITDs, but the means by which such neurons represent ITD is a contentious issue. Recent studies question whether the classical general model (the Jeffress model) applies across species. Here we show that ITD coding strategies of different species can be explained by a unifying principle: that the ITDs an animal naturally encounters should be coded with maximal accuracy. Using statistical techniques and a stochastic neural model, we demonstrate that the optimal coding strategy for ITD depends critically on head size and sound frequency. For small head sizes and/or low-frequency sounds, the optimal coding strategy tends towards two distinct sub-populations tuned to ITDs outside the range created by the head. This is consistent with recent observations in small mammals. For large head sizes and/or high frequencies, the optimal strategy is a homogeneous distribution of ITD tunings within the range created by the head. This is consistent with observations in the barn owl. For humans, the optimal strategy to code ITDs from an acoustically measured distribution depends on frequency; above 400 Hz a homogeneous distribution is optimal, and below 400 Hz distinct sub-populations are optimal. 相似文献
149.
Apart from echolocation and the pursuit of prey by bats, the function of ultrasound in animal communication is poorly understood. This is mainly because of the broad range of responses that it can evoke and the widely varied contexts in which it is used (for example, in rodents of the Muridae family it may indicate distress in infants or a sexual or predatory encounter in adults). Here we find that a purely ultrasonic signal is produced in the wild by a rodent of the Sciuridae family, Richardson's ground squirrel, and show that its function is to warn conspecifics of impending danger. To our knowledge, ultrasonic alarm calls have not previously been detected in any animal group, despite their twin advantages of being highly directional and inaudible to key predators. 相似文献
150.
A critical step in self-motion perception and spatial awareness is the integration of motion cues from multiple sensory organs that individually do not provide an accurate representation of the physical world. One of the best-studied sensory ambiguities is found in visual processing, and arises because of the inherent uncertainty in detecting the motion direction of an untextured contour moving within a small aperture. A similar sensory ambiguity arises in identifying the actual motion associated with linear accelerations sensed by the otolith organs in the inner ear. These internal linear accelerometers respond identically during translational motion (for example, running forward) and gravitational accelerations experienced as we reorient the head relative to gravity (that is, head tilt). Using new stimulus combinations, we identify here cerebellar and brainstem motion-sensitive neurons that compute a solution to the inertial motion detection problem. We show that the firing rates of these populations of neurons reflect the computations necessary to construct an internal model representation of the physical equations of motion. 相似文献