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971.
Sympatric populations of Cophosaurus texanus and Callisaurus draconoides were periodically sampled from March 1973 through April 1974 at Burro Creek, Mohave County, Arizona. Callisaurus were also sampled at Rock Valley, Nye County, Nevada. Sex ratios were skewed in favor of males in the adult Cophosaurus but were equal in both adult populations of Callisaurus. Both species became sexually mature as yearlings. Mean clutch sizes were 3.55 (±0.83) for Cophosaurus, and 4.25 (±1.08) and 5.07 (±1.33) for Callisaurus at Burro Creek and Rock Valley respectively. Evidence of multiple clutches was exhibited by both species. Egg weight/body weight ratios for both species and clutch weight/body weight ratios for Cophosaurus were notably smaller than previously reported. At Burro Creek both species were highly insectivorus, with orthopterans comprising the largest food group of each. Niche overlap for food was high at the ordinal level, but at the familial level it is apparent that Callisaurus probably fed in the more xeric areas of the riparian habitat. No differences were found in the temperature responses of these two lizards. However, minor temporal separations and substantial spatial partitioning were observed. Callisaurus preferred sandy open areas, while Cophosaurus preferred the presence of some rocks and boulders. 相似文献
972.
The idea of atomic-resolution holography has its roots in the X-ray work of Bragg and in Gabor's electron interference microscope. Gabor's lensless microscope was not realized in his time, but over the past twelve years there has been a steady increase in the number of reports on atomic-resolution holography. All of this work involves the use of electrons or hard X-rays to produce the hologram. Neutrons are often unique among scattering probes in their interaction with materials: for example, the relative visibility of hydrogen and its isotopes is a great advantage in the study of polymers and biologically relevant materials. Recent work proposed that atomic-resolution holography could be achieved with thermal neutrons. Here we use monochromatic thermal neutrons, adopting the inside-source concept of Sz?ke, to image planes of oxygen atoms located above and below a single hydrogen atom in the oxide mineral simpsonite. 相似文献
973.
974.
The activation of ubiquitin and related protein modifiers is catalysed by members of the E1 enzyme family that use ATP for the covalent self-attachment of the modifiers to a conserved cysteine. The Escherichia coli proteins MoeB and MoaD are involved in molybdenum cofactor (Moco) biosynthesis, an evolutionarily conserved pathway. The MoeB- and E1-catalysed reactions are mechanistically similar, and despite a lack of sequence similarity, MoaD and ubiquitin display the same fold including a conserved carboxy-terminal Gly-Gly motif. Similar to the E1 enzymes, MoeB activates the C terminus of MoaD to form an acyl-adenylate. Subsequently, a sulphurtransferase converts the MoaD acyl-adenylate to a thiocarboxylate that acts as the sulphur donor during Moco biosynthesis. These findings suggest that ubiquitin and E1 are derived from two ancestral genes closely related to moaD and moeB. Here we present the crystal structures of the MoeB-MoaD complex in its apo, ATP-bound, and MoaD-adenylate forms, and highlight the functional similarities between the MoeB- and E1-substrate complexes. These structures provide a molecular framework for understanding the activation of ubiquitin, Rub, SUMO and the sulphur incorporation step during Moco and thiamine biosynthesis. 相似文献
975.
Clustering of organisms can be a consequence of social behaviour, or of the response of individuals to chemical and physical cues. Environmental variability can also cause clustering: for example, marine turbulence transports plankton and produces chlorophyll concentration patterns in the upper ocean. Even in a homogeneous environment, nonlinear interactions between species can result in spontaneous pattern formation. Here we show that a population of independent, random-walking organisms ('brownian bugs'), reproducing by binary division and dying at constant rates, spontaneously aggregates. Using an individual-based model, we show that clusters form out of spatially homogeneous initial conditions without environmental variability, predator-prey interactions, kinesis or taxis. The clustering mechanism is reproductively driven-birth must always be adjacent to a living organism. This clustering can overwhelm diffusion and create non-poissonian correlations between pairs (parent and offspring) or organisms, leading to the emergence of patterns. 相似文献
976.
John R. Spence 《西北部美国博物学家》2011,65(1)
Symphyotrichum expansum (Puepp ex Spreng.) Nesom is reported new to Utah from the Escalante River drainage. A major range extension is reported for Aralia racemosa L. in the Escalante drainage, and additional populations are reported of the rare species Imperata brevifolia Vasey in Utah, including the 1st record for the Grand Staircase--Escalante National Monument. Heterotheca grandiflora Nutt. is reported new to north central Arizona. New locations and notes on an additional 22 rare species in Glen Canyon National Recreation Area are listed. 相似文献
977.
Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4 /* 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;} Carebareia, n. gen., and its type - species, C. johnstoni, n. sp., are described. The genus Quadraseta Brennan, 1970, is redefined and a key to the 11 included species given. Four new species, Quadraseta tachirensis, holotype ex Akodon sp., Q. rotstieri, ex Proechimys guyannensis, Q. mirandae, holotype ex Oryzomys albigularis, and Q. falconensis, ex Sylvilagus floridanus, are described. 相似文献
978.
Rose Ella Warner 《西北部美国博物学家》2011,36(4)
A new species of weevil, Phyllotrox canyonaceris Warner, is described, new synonomy, and distribution records of eight species of the genus Phyllotrox in North America are given. 相似文献
979.
Richard L. Wallace J. S. Griffith Jr. D. M. Daley Patrick J. Connolly G. B. Beckham 《西北部美国博物学家》2011,44(2)
Cottus greenei, a potentially threatened species endemic to Idaho, was collected from 49 localities in 25 springs/streams in south central Idaho. Most localities were along the north bank of the Snake River in waters of the Thousand Springs formation, Gooding County. One population was found in a spring in the main Snake River. Another sculpin, Cottus bairdi, was collected with C. greenei at 23 locations in 16 springs/streams. Confusion concerning the type locality of Cottus greenei is discussed. 相似文献
980.
L. Vanderkelen J. M. Van Herreweghe K. G. A. Vanoirbeek G. Baggerman B. Myrnes P. J. Declerck I. W. Nilsen C. W. Michiels L. Callewaert 《Cellular and molecular life sciences : CMLS》2011,68(6):1053-1064
Lysozymes are antibacterial effectors of the innate immune system in animals that hydrolyze peptidoglycan. Bacteria have evolved
protective mechanisms that contribute to lysozyme tolerance such as the production of lysozyme inhibitors, but only inhibitors
of chicken (c-) and invertebrate (i-) type lysozyme have been identified. We here report the discovery of a novel Escherichia coli inhibitor specific for goose (g-) type lysozymes, which we designate PliG (periplasmic lysozyme inhibitor of g-type lysozyme).
Although it does not inhibit c- or i-type lysozymes, PliG shares a structural sequence motif with the previously described
PliI and MliC/PliC lysozyme inhibitor families, suggesting a common ancestry and mode of action. Deletion of pliG increased the sensitivity of E. coli to g-type lysozyme. The existence of inhibitors against all major types of animal lysozyme and their contribution to lysozyme
tolerance suggest that lysozyme inhibitors may play a role in bacterial interactions with animal hosts. 相似文献