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121.
Molecular evidence for genetic mixing of Arctic and Antarctic subpolar populations of planktonic foraminifers 总被引:16,自引:0,他引:16
Bipolarity, the presence of a species in the high latitudes separated by a gap in distribution across the tropics, is a well-known pattern of global species distribution. But the question of whether bipolar species have evolved independently at the poles since the establishment of the cold-water provinces 16-8 million years ago, or if genes have been transferred across the tropics since that time, has not been addressed. Here we examine genetic variation in the small subunit ribosomal RNA gene of three bipolar planktonic foraminiferal morphospecies. We identify at least one identical genotype in all three morphospecies in both the Arctic and Antarctic subpolar provinces, indicating that trans-tropical gene flow must have occurred. Our genetic analysis also reveals that foraminiferal morphospecies can consist of a complex of genetic types. Such occurrences of genetically distinct populations within one morphospecies may affect the use of planktonic foraminifers as a palaeoceanographic proxy for climate change and necessitate a reassessment of the species concept for the group. 相似文献
122.
Horses, donkeys, and therefore, probably all equids, secrete a nonglycosylated, progesterone-dependent, 19-kDa protein (P19)
into the uterine lumen during early pregnancy, and significant quantities of it are taken up by the developing conceptus.
Sequence analysis and structural modelling have identified P19 as a lipocalin with greatest similarity to the murine major
urinary protein lipocalins. However, lack of strong identity with any particular group of lipocalins and several unusual structural
features, including a unique amino acid triplet within one of the invariant domains and an unusual external tryptophan residue,
classify it as a new member of the lipocalin family. P19 is therefore likely to be a transport protein involved in supporting
early embryonic development. Preliminary evidence using recombinant-derived P19 and fluorescently tagged ligands suggests
that it may transport a fatty acid or retinol-like molecule. Although an initial search failed to identify homologues of P19
in other mammals, they may nevertheless exist but are synthesised and secreted in much smaller quantities, making them difficult
to detect. Equids appear to need particularly large quantities of the protein during early pregnancy because of the unusually
late implantation in this species and the presence of a capsule surrounding the conceptus until about day 23 of gestation. 相似文献
123.
The ability to cool and slow atoms with light for subsequent trapping allows investigations of the properties and interactions of the trapped atoms in unprecedented detail. By contrast, the complex structure of molecules prohibits this type of manipulation, but magnetic trapping of calcium hydride molecules thermalized in ultra-cold buffer gas and optical trapping of caesium dimers generated from ultra-cold caesium atoms have been reported. However, these methods depend on the target molecules being paramagnetic or able to form through the association of atoms amenable to laser cooling, respectively, thus restricting the range of species that can be studied. Here we describe the slowing of an adiabatically cooled beam of deuterated ammonia molecules by time-varying inhomogeneous electric fields and subsequent loading into an electrostatic trap. We are able to trap state-selected ammonia molecules with a density of 10(6) cm(-3) in a volume of 0.25 cm3 at temperatures below 0.35 K. We observe pronounced density oscillations caused by the rapid switching of the electric fields during loading of the trap. Our findings illustrate that polar molecules can be efficiently cooled and trapped, thus providing an opportunity to study collisions and collective quantum effects in a wide range of ultra-cold molecular systems. 相似文献
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126.
Sarcobatus Nees., a genus of North American halophytic shrubs, consists of 2 species: S. vermiculatus (Hook.) Torr. ( n = 18, 36), which is widespread in North America, and S. baileyi Cov ( n = 54), endemic to Nevada. Within S. vermiculatus , populations of n = 36 are widely distributed, whereas populations of n = 18 are found only in the Sonoran Desert, northern California, and northwestern Great Plains, locations at the periphery of the species range. Although the chromosome number of n = 18 is apparently a tetraploid, failure to form and n = 27 race intermediate to those of n = 18 and n = 36 suggests than n = 18 S. vermiculatus is of significant age and that it behaves chromosomally as a diploid. Sacrobatus has a long fossil pollen record and endured Pleistocene climatic extremes with little range displacement. 相似文献
127.
Goudie DR D'Alessandro M Merriman B Lee H Szeverényi I Avery S O'Connor BD Nelson SF Coats SE Stewart A Christie L Pichert G Friedel J Hayes I Burrows N Whittaker S Gerdes AM Broesby-Olsen S Ferguson-Smith MA Verma C Lunny DP Reversade B Lane EB 《Nature genetics》2011,43(4):365-369
Multiple self-healing squamous epithelioma (MSSE), also known as Ferguson-Smith disease (FSD), is an autosomal-dominant skin cancer condition characterized by multiple squamous-carcinoma-like locally invasive skin tumors that grow rapidly for a few weeks before spontaneously regressing, leaving scars. High-throughput genomic sequencing of a conservative estimate (24.2 Mb) of the disease locus on chromosome 9 using exon array capture identified independent mutations in TGFBR1 in three unrelated families. Subsequent dideoxy sequencing of TGFBR1 identified 11 distinct monoallelic mutations in 18 affected families, firmly establishing TGFBR1 as the causative gene. The nature of the sequence variants, which include mutations in the extracellular ligand-binding domain and a series of truncating mutations in the kinase domain, indicates a clear genotype-phenotype correlation between loss-of-function TGFBR1 mutations and MSSE. This distinguishes MSSE from the Marfan syndrome-related disorders in which missense mutations in TGFBR1 lead to developmental defects with vascular involvement but no reported predisposition to cancer. 相似文献
128.
129.
Stewart B. Peck 《西北部美国博物学家》2011,41(2)
Seven large caves in the Uinta Mountains, Utah, were surveyed for their invertebrate faunas. Thirty-eight species were found, and 30 of these are typical cave inhabitants. Diptera are the predominant group. Cave-restricted species are an amphipod, two diplurans, and possibly a Rhagidia mite. The caves were probablv uninhabitable in the past glacial because of severe periglacial environmental conditions, and the faunas have moved into the present cave sites since deglaciation of the Uintas. 相似文献
130.
Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4 st1\:*{behavior:url(#ieooui) } /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-qformat:yes; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:11.0pt; font-family:"Calibri","sans-serif"; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-fareast-font-family:"Times New Roman"; mso-fareast-theme-font:minor-fareast; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;} Hydroperla crosbyi in Texas exhibited a univoltine, fast life cycle over the three - year study period. Adults emerged in February – March when mean daily stream temperature reached ca. 15 C. Reared females in the lab deposited up to three egg masses. Mean fecundity of dissected females was 787 eggs/female. Oviposition in the field was observed and described. Eggs were triangular in cross section, brown, and measured 400 µ m × 535 µ m. They underwent an ca. seven-month diapause until mean daily stream temperature decreased to 18 C. Eyespots appeared, and hatching followed in two to three weeks. First instar nymphs were measured and described. Male and female nymphs underwent 12 and 14 instars, respectively, and could be sexed by the sixth. Fast growth occurred in the coldest season and Simuliidae and Chironomidae larvae were preferred food throughout development. Eggs contained a mean of 6.21 cal/mg. Ash - free mean caloric value of last instar nymphs was 6.0 cal/mg. Adult males and females lost 33.8 percent and 57.6 percent, respectively, of their caloric pool through their ca. 12 days of life. 相似文献