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1.
For either clinical or research purposes, the timing of the nocturnal onset in production of the urinary melatonin metabolite 6-sulfatoxymelatonin (UaMT6s-onset), has been proposed as a reliable and robust marker of circa-dian phase. However, given that most circadian rhythms show cycle-to-cycle variability, the statistical reliability of phase estimates obtained from a single study using UaMT6s-onset remains to be determined. Following 2 weeks of sleep diary and wrist actigraphy, 15 young, healthy good sleepers participated in four UaMT6s sampling sessions spaced 1 day apart. During the sampling sessions subjects remained indoors under low light conditions and hourly urine samples were collected from 19:00 to 02:00 h. Samples were subsequently assayed for UaMT6s using standard radioimmunographic techniques. UaMT6s-onset was determined by the time at which melatonin production exceeded the average of three proceeding trials by 100%. Sleep onset times were derived from sleep diary and actigraphic measures taken before the melatonin collection nights. We found that there was no significant variation between nights in group mean UaMT6s-onset times, and intraindividual variability was small. In addition, UaMT6s-onset times were highly and significantly correlated between nights (grand mean r = 0.804). Our results suggest that within 95% confidence interval limits, individual UaMT6s-onset estimates obtained from a single night UaMT6s-onset study can be used to predict subsequent UaMT6s-onset times within ±97 min. A close temporal relationship was also found between the timing of UaMT6s-onset and sleep onset. Overall, our results suggest that under entrained conditions single-session UaMT6s-onset studies can provide reliable individual UaMT6s-onset phase estimates and that the protocol described in this study is a practical and noninvasive methodology. (Chronobiology International, 13(6), 411-421, 1996) 相似文献
2.
3.
Flowering phenology has normally been viewed as fundamental to a plant species' reproductive ecology. Researchers in the field have emphasized the adaptive importance of flowering at a particular time relative to other individuals in the population, or other species in the community. An alternative view, however, is that flowering phenology is a trait that may not be under strong selection, and this may have allowed some variation to appear in populations by chance. 相似文献
4.
H. Walter Lack 《Plant Systematics and Evolution》1979,131(1-2):35-52
Three species of the genusPicris L. are native in Tropical Africa:P. abyssinica
Sch. Bip. (Ethiopia),P. xylopoda
Lack, spec. nova (Nigeria, Ethiopia) andP. humilis DC. (Senegal, Mali). There are indications that the two perennial species,P. abyssinica andP. xylopoda, are related to and have evolved from a primitive Central Asiatic stock in a manner parallel to many African species ofCrepis L.P. humilis, on the other hand, is a small annual plant with a high number of derived characters. The introduced species of European origin growing south of the Sahara are briefly mentioned. 相似文献
5.
The five step synthesis of 7alpha-hydroxycholesterol utilizes the solvolysis of 7alpha-bromocholesterol benzoate with potassium acetate in acetic acid as the key step in controlling the stereospecificity of the reaction sequence. This reaction yields 7alpha-acetoxycholesterol benzoate with retention of configuration at position seven. The diester is readily reduced with lithium aluminum to 7alpha-hydroxycholesterol. 相似文献
6.
David Lack 《Bird Study》2013,60(1):14-17
Capsule This study is the first ever documented evidence of an interglacial refugium during the Last Interglacial for birds in Anatolia and suggests the need of a re-examination of the effects of the Last Interglacial on the geographic distribution and genetic structure of species.Aims We tested whether, in accordance with the ‘refugia within refugia’ model, multiple refugia existed for Kruper's Nuthatch Sitta krueperi during the Last Glacial Maximum or the species survived along the coastal belt of Anatolia through the Late Quaternary glacial–interglacial cycles.Methods An ecological niche model was developed to predict the geographic distribution of Kruper's Nuthatch under reconstructed past (the Last Interglacial and the Last Glacial Maximum), present, and projected future bioclimatic conditions. Also, robust coalescent-based analyses were used to assess demographic events over the history of Kruper's Nuthatch.Results Kruper's Nuthatch survived the Last Glacial Maximum almost along the coastal belt of Anatolia, but not in multiple refugia, and surprisingly, contrary to expectations, it survived the Last Interglacial in southern Anatolia, but not along the coastal belt of Anatolia.Conclusion A kind of the ‘refugia within refugia’ model (i.e. the ‘refugium within refugium’ model) was supported because range shifts took place within Anatolia (itself also a refugium) for Kruper's Nuthatch. 相似文献
7.
Justin B. Lack Amir Yassin Quentin D. Sprengelmeyer Evan J. Johanning Jean R. David John E. Pool 《Ecology and evolution》2016,6(16):5893-5906
Understanding the physiological and genetic basis of growth and body size variation has wide‐ranging implications, from cancer and metabolic disease to the genetics of complex traits. We examined the evolution of body and wing size in high‐altitude Drosophila melanogaster from Ethiopia, flies with larger size than any previously known population. Specifically, we sought to identify life history characteristics and cellular mechanisms that may have facilitated size evolution. We found that the large‐bodied Ethiopian flies laid significantly fewer but larger eggs relative to lowland, smaller‐bodied Zambian flies. The highland flies were found to achieve larger size in a similar developmental period, potentially aided by a reproductive strategy favoring greater provisioning of fewer offspring. At the cellular level, cell proliferation was a strong contributor to wing size evolution, but both thorax and wing size increases involved important changes in cell size. Nuclear size measurements were consistent with elevated somatic ploidy as an important mechanism of body size evolution. We discuss the significance of these results for the genetic basis of evolutionary changes in body and wing size in Ethiopian D. melanogaster. 相似文献
8.
An NMR spectroscopy study ((31)P, (1)H, (13)C) of the postulated crosslinking mechanism of sodium trimetaphosphate (STMP) on polysaccharides is reported using methyl alpha-D-glucopyranoside as a model. In a first step, reaction of STMP with Glc-OMe gives grafted sodium tripolyphosphate (STPP(g)). On the one hand, STTP(g) can react with a second alcohol functionality to give a crosslinked monophosphate. On the other hand, a monophosphate (grafted phosphate) could be obtained by alkaline degradation of STPP(g). NMR spectroscopy allows to detect the various species formed and to obtain the crosslinking density of STMP-polysaccharides hydrogels. 相似文献
9.
A. A. Echelle J. C. Hackler J. B. Lack S. R. Ballard J. Roman S. F. Fox D. M. LeslieJr. R. A. Van Den Bussche 《Conservation Genetics》2010,11(4):1375-1387
A previous mtDNA study indicated that female-mediated gene flow was extremely rare among alligator snapping turtle populations
in different drainages of the Gulf of Mexico. In this study, we used variation at seven microsatellite DNA loci to assess
the possibility of male-mediated gene flow, we augmented the mtDNA survey with additional sampling of the large Mississippi
River System, and we evaluated the hypothesis that the consistently low within-population mtDNA diversity reflects past population
bottlenecks. The results show that dispersal between drainages of the Gulf of Mexico is rare (F
STmsat
= 0.43, ΦSTmtDNA = 0.98). Past range-wide bottlenecks are indicated by several genetic signals, including low diversity for microsatellites
(1.1–3.9 alleles/locus; H
e = 0.06–0.53) and mtDNA (h = 0.00 for most drainages; π = 0.000–0.001). Microsatellite data reinforce the conclusion from mtDNA that the Suwannee River population might eventually
be recognized as a distinct taxonomic unit. It was the only population showing fixation or near fixation for otherwise rare
microsatellite alleles. Six evolutionarily significant units are recommended on the basis of reciprocal mtDNA monophyly and
high levels of microsatellite DNA divergence. 相似文献
10.