58 resultados para Circadian Clock
Resumo:
An out-of-Africa dispersal route has been proposed for many organisms, including modern man. However, counter examples of in-to-Africa dispersal routes are less common. In the present article, the phylogenetic relationships within the Labeoninae, a subfamily of cyprinid fishes distributed in Asia and Africa, were analyzed to investigate the biogeographic processes governing the modern distribution of these Asian and African cyprinids. The mitochondrial DNA cytochrome b gene was used as a molecular marker. The phylogenetic analysis indicated that the subfamily Labeoninae is a monophyletic group, with some Asian labeonins located at the basal position. Two subclades were found that contained both African and Asian species, which highlighted a need for further biogeographic analysis. Based on this analysis, it is proposed that the centre of origin of the Labeoninae was in East Asia. Molecular clock estimation suggests that the Labeoninae arose by the Early Miocene (similar to 23 MYA) during the period of the second Tibetan uplift. Subsequently, two dispersal events of labeonins from Asia into Africa occured in the Early Miocene (similar to 20 MYA) and Late Miocene (similar to 9 MYA) and serve as examples counter to out-of-Africa dispersal.
Resumo:
The genus Sinocyclocheilus is distributed in Yun-Gui Plateau and its surrounding region only, within more than 10 cave species showing different degrees of degeneration of eyes and pigmentation with wonderful adaptations. To present, published morphological and molecular phylogenetic hypotheses of Sinocyclocheilus from prior works are very different and the relationships within the genus are still far from clear. We obtained the sequences of cytochrome b (cyt b) and NADH dehydrogenase subunit 4 (ND4) of 34 species within Sinocyclocheilus, which represent the most dense taxon sampling to date. We performed Bayesian mixed models analyses with this data set. Under this phylogenetic framework, we estimated the divergence times of recovered clades using different methods under relaxed molecular clock. Our phyloegentic results supported the monophyly of Sinocyclocheilus and showed that this genus could be subdivided into 6 major clades. In addition, an earlier finding demonstrating the polyphyletic of cave species and the most basal position of S. jii was corroborated. Relaxed divergence-time estimation suggested that Sinocyclocheilus originated at the late Miocene, about 11 million years ago (Ma), which is older than what have been assumed.
Resumo:
The genus Sarcocheilichthys is a group of small cyprinid fishes comprising 10 species/sub-species widely distributed in East Asia, which represents a valuable model for understanding the speciation of freshwater fishes in East Asia. In the present study, the molecular phylogenetic relationship of the genus Sarcocheilichthys was investigated using a 1140 bp section of the mitochondrial cytochrome b gene. Two different tree-building methods, maximum parsimony (MP) and Bayesian methods, yielded trees with almost the same topology, yielding high bootstrap values or posterior probabilities. The results showed that the genus Sarcocheilichthys consists of two large clades, clades I and II. Clade I contains Sarcocheilichthys lacustris, Sarcocheilichthys sinensis and Sarcocheilichthys parvus, with S. parvus at a basal position. In clade II, Sarcocheilichthys variegatus microoculus is at a basal position; samples of the widespread species, Sarcocheilichthys nigripinnis, form a large subclade containing another valid species Sarcocheilichthys czerskii. Sarcocheilichthys kiangsiensis is retained at an intermediate position. Since S. czerskii is a valid species in the S. nigripinnis clade, remaining samples of S. nigripinnis form a paraphyly. This speciation process is attributed to geographical isolation and special environmental conditions experienced by S. czerskii and stable environments experienced by the other S. nigripinnis populations. This type of speciation process was suggested to be very common. Samples of Sarcocheilichthys sinensis sinensis and Sarcocheilichthys sinensis fukiensis that did not form their own monophyletic groups suggest an early stage of speciation and support their sub-species status. Molecular clock analysis indicates that the two major lineages of the genus Sarcocheilichthys, clades I and II diverged c. 8.89 million years ago (mya). Sarcocheilichthys v. microoculus from Japan probably diverged 4.78 mya from the Chinese group. The northern-southern clades of S. nigripinnis began to diverge c. 2.12 mya, while one lineage of S. nigripinnis evolved into a new species, S. czerski, c. 0.34 mya. (C) 2008 The Authors Journal compilation (C) 2008 The Fisheries Society of the British Isles.
Resumo:
The Sox gene family is found in a broad range of animal taxa and encodes important gene regulatory proteins involved in a variety of developmental processes. We have obtained clones representing the HMG boxes of twelve Sox genes from grass carp (Ctenopharyngodon idella), one of the four major domestic carps in China. The cloned Sox genes belong to group B1, B2 and C. Our analyses show that whereas the human genome contains a single copy of Sox4, Sox11 and Sox14, each of these genes has two co-orthologs in grass carp, and the duplication of Sox4 and Sox11 occurred before the divergence of grass carp and zebrafish, which support the "fish-specific whole-genome duplication" theory. An estimation for the origin of grass carp based on the molecular clock using Sox1, Sox3 and Sox11 genes as markers indicates that grass carp (subfamily Leuciscinae) and zebrafish (subfamily Danioninae) diverged approximately 60 million years ago. The potential uses of Sox genes as markers in revealing the evolutionary history of grass carp are discussed.
Resumo:
The Otocephala, a clade including ostariophysan and clupeomorph telcosts, represents about a quarter of total fish species diversity, with about 1000 gencra and more than 7000 species. A series of recent papers have defended that the origin of this clade and of its major groups may be significantly older than the oldest fossils of each of these groups suggest. Some of these recent papers explicitly defend a Pangean origin for some otocephalan groups Such as the Siluriformes or Cypriniformes. To know whether or not the otocephalans as a whole, and particularly the mainly freshwater, cosmopolitan otophysans could have originated before the splitting of the Pangean Supercontinent is of extreme importance, since otophysan fishes are among the most useful animal groups for the determination of historical continental relationships. In the present work we examined divergence times for each major otocephalan group by an analysis of complete mtDNA sequences, in order to investigate if these divergence times support the hypotheses advanced in recent studies. The complete mtDNA sequences of nine representative non-otocephalan fish species and of twenty-one representative otocephalan species was compared. The present study is thus, among the studies dealing with molecular divergence times of telcosts, the one in which a greater number of otocephalan species are included. The divergence times obtained support that the major otocephalan groups had a much older origin than the oldest fossil records available for these groups suggest. The origin of the Otocephala is estimated as having occurred about 282 Mya, with the origin of the Otophysi being estimated at about 251 Mya. (c) 2005 Elsevier B.V. All rights reserved.
Resumo:
The family Sisoridae is one of the largest and most diverse Asiatic catfish families, most species occurring in the water systems of the Qinhai-Tibetan Plateau and East Himalayas. To date published morphological and molecular phylogenetics hypotheses of sisorid catfishes are part congruent, and there are some areas of significant disagreement with respect to intergeneric relationships. We used mitochondrial cytochrome b and 16S rRNA gene sequences to clarify existing gaps in phylogenetics and to test conflicting vicariant and dispersal biogeographical hypotheses of Chinese sisorids using dispersal-vicariance analysis and weighted ancestral area analysis in combination with palaeogeographical data as well as molecular clock calibration. Our results suggest that: (1) Chinese sisorid catfishes form a monophyletic group with two distinct clades, one represented by (Gagata (Bagarius, Glyptothorax)) and the other by (glyptosternoids, Pseudecheneis); (2) the glyptosternoid is a monophyletic group and Glyptosternum, Glaridoglanis, and Exostoma are three basal species having a primitive position among it; (3) a hypothesis referring to Pseudecheneis as the sister group of the glyptosternoids, based on morphological evidence, is supported; (4) the genus Pareuchiloglanis, as presently defined, is not monophyletic; (5) congruent with previous hypotheses, the uplift of Qinghai-Tibetan Plateau played a primary role in the speciation and radiation of the Chinese sisorids; and (6) an evolutionary scenario combining aspects of both vicariance and dispersal theory is necessary to explain the distribution pattern of the glyptosternoids. In addition, using a cytochrome b substitution rate of 0.91% per million years and 0.23% for 16S rRNA, we tentatively date that the glyptosternoids most possibly originated in Oligocene-Miocene boundary (19-24Myr), and radiated from Miocene to Pleistocene, along with a center of origin in the Irrawaddy-Tsangpo drainages and several rapid speciation in a relatively short time. (c) 2005 Elsevier Inc. All rights reserved.
Resumo:
Molecular phylogeny of three genera containing nine species and subspecies of the specialized schizothoracine fishes are investigated based on the complete nucleotide sequence of mitochondrial cytochrome b gene. Meantime relationships between the main cladogenetic events of the specialized schizothoracine fishes and the stepwise uplift of the Qinghai-Tibetan Plateau are also conducted using the molecular clock, which is calibrated by geological isolated events between the upper reaches of the Yellow River and the Qinghai Lake. Results indicated that the specialized schizothoracine fishes are not a monophyly. Five species and subspecies of Ptychobarbus form a monophyly. But three species of Gymnodiptychus do not form a monophyly. Gd. integrigymnatus is a sister taxon of the highly specialized schizothoracine fishes while Gd. pachycheilus has a close relation with Gd. dybowskii, and both of them are as a sister group of Diptychus maculatus. The specialized schizothoracines fishes might have originated during the Miocene (about 10 MaBP), and then the divergence of three genera happened during late Miocene (about 8 MaBP). Their main specialization occurred during the late Pliocene and Pleistocene (3.54-0.42 MaBP). The main cladogenetic events of the specialized schizothoracine fishes are mostly correlated with the geological tectonic events and intensive climate shift happened at 8, 3.6, 2.5 and 1.7 MaBP of the late Cenozoic. Molecular clock data do not support the hypothesis that the Qinghai-Tibetan Plateau uplifted to near present or even higher elevations during the Oligocene or Miocene, and neither in agreement with the view that the plateau uplifting reached only to an altitude of 2000 in during the late Pliocene (about 2.6 MaBP).
Resumo:
A 1.55 mu m InGaAsP-InP two-section DFB laser with a variable ridge width has been fabricated. Self-pulsations with frequencies around 3 GHz and 40 GHz are observed. The pulsation mechanisms related to the two frequencies are discussed and the tunability of generated self-pulsations is studied.
Resumo:
A 1.55 mu m InGaAsP-InP index-coupled two-section DFB self-pulsation laser (SPL) with a varied ridge width has been fabricated. A record wide self-pulsation tuning range above 450 GHz has been achieved for this index-coupled DFB SPL. Furthermore, frequency locking to an optically injected modulated signal is successfully demonstrated.
Resumo:
A scheme for hi-fi all-optical continuously tunable delay is proposed. The signal wavelength is converted to a desired idler wavelength and converted back after being delayed by a high linear-chirp-rate (HLCR) fiber Bragg grating (FBG) based on four-wave mixing (FWM) in a highly-nonlinear photonic crystal fiber (HN-PCF). In our experiment, 400 ps (more than 8 full width of half maximum, FWHM) tunable delay is achieved for a 10 GHz clock pulse with relative pulse width broaden ratio (RPWBR) of 2.08%. The power penalty is only 0.3 dB at 10(-9) BER for a 10 Gb/s 2(31)-1 pseudo random bit sequence (PRBS) data. (c) 2009 Elsevier B.V. All rights reserved.
Resumo:
This paper presents a novel vision chip for high-speed target tracking. Two concise algorithms for high-speed target tracking are developed. The algorithms include some basic operations that can be used to process the real-time image information during target tracking. The vision chip is implemented that is based on the algorithms and a row-parallel architecture. A prototype chip has 64 x 64 pixels is fabricated by 0.35 pm complementary metal-oxide-semiconductor transistor (CMOS) process with 4.5 x 2.5 mm(2) area. It operates at a rate of 1000 frames per second with 10 MHz chip main clock. The experiment results demonstrate that a high-speed target can be tracked in complex static background and a high-speed target among other high-speed objects can be tracked in clean background.
Resumo:
A group of prototype integrated circuits are presented for a wireless neural recording micro-system. An inductive link was built for transcutaneous wireless power transfer and data transmission. Power and data were transmitted by a pair of coils on a same carrier frequency. The integrated receiver circuitry was composed of a full-wave bridge rectifier, a voltage regulator, a date recovery circuit, a clock recovery circuit and a power detector. The amplifiers were designed with a limited bandwidth for neural signals acquisition. An integrated FM transmitter was used to transmit the extracted neural signals to external equipments. 16.5 mW power and 50 bps - 2.5 Kbps command data can be received over 1 MHz carrier within 10 mm. The total gain of 60 dB was obtained by the preamplifier and a main amplifier at 0.95Hz - 13.41 KHz with 0.215 mW power dissipation. The power consumption of the 100 MHz ASK transmitter is 0.374 mW. All the integrated circuits operated under a 3.3 V power supply except the voltage regulator.
Resumo:
A novel low-power digital baseband circuit for UHF RFID tag with sensors is presented in this paper. It proposes a novel baseband architecture and a new operating scheme to fulfill the sensor functions and to reduce power consumption. It is also compatible with the EPC C1G2 UHF RFID protocol. It adopts some advanced low power techniques for system design and circuit design: adaptive clock-gating, multi-clock domain and asynchronous circuit. The baseband circuit is implemented in 0.18um 1P3M standard CMOS process. ne chip area is 0.28 mm(2) excluding test pads. Its power consumption is 25uW under 1.1V power supply.
Resumo:
This paper proposes an embedded ultra low power nonvolatile memory in a standard CMOS logic process. The memory adopts a bit cell based on the differential floating gate PMOS structure and a novel operating scheme. It can greatly improve the endurance and retention characteristic and make the area/bit smaller. A new high efficiency all-PMOS charge pump is designed to reduce the power consumption and to increase the power efficiency. It eliminates the body effect and can generate higher output voltage than conventional structures for a same stage number. A 32-bit prototype chip is fabricated in a 0.18 mu m 1P4M standard CMOS logic process and the core area is 0.06 mm(2). The measured results indicate that the typical write/erase time is 10ms. With a 700 kHz clock frequency, power consumption of the whole memory is 2.3 mu A for program and 1.2 mu A for read at a 1.6V power supply.
Resumo:
An ultra low power non-volatile memory is designed in a standard CMOS process for passive RFID tags. The memory can operate in a new low power operating scheme under a wide supply voltage and clock frequency range. In the charge pump circuit the threshold voltage effect of the switch transistor is almost eliminated and the pumping efficiency of the circuit is improved. An ultra low power 192-bit memory with a register array is implemented in a 0.18 mu M standard CMOS process. The measured results indicate that, for the supply voltage of 1.2 volts and the clock frequency of 780KHz, the current consumption of the memory is 1.8 mu A (3.6 mu A) at the read (write) rate of 1.3Mb/s (0.8Kb/s).