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991.
Recent studies have demonstrated that changes in scale number are correlated with ecological variables such as precipitation,
and this suggests that scale number may be under selection to maintain water balance in reptiles. Here, we present new evidence
that variation in scale numbers within and among species of Anolis lizards is under ecologically based natural selection. We measured scalation of the brown anole, Anolis sagrei, in two habitat types on each of five islands in the Bahamas. We also measured scalation for 12 species of anole representing
six different ecomorphs from the Greater Antilles. Within populations of A. sagrei, scale numbers increased with increasing precipitation and with decreasing temperature in open arid habitats. Variation measured
among species of Anolis from the Greater Antilles showed similar patterns with temperature, precipitation, and elevation. Independent contrasts using
scale count data indicated that variation in scale number was congruent within and between species, even after accounting
for the influence of phylogeny. We measured natural selection (survival to maturity) on scale number in A. sagrei over two different habitat types in the Bahamas. Patterns of natural selection were congruent with the correlational results
described. Finally, results from a breeding experiment in the laboratory provide preliminary evidence that variation in scale
number is heritable, and suggests a mechanism for generating these correlations. Our results provide new evidence that the
diversification of anoles has been shaped by natural selection and that ecologically based selection pressures help explain
diversification at both the population and species levels.
Co-ordinating editor: M. Klaassen 相似文献
992.
Phosphorylation of Chk1 by ATR is antagonized by a Chk1-regulated protein phosphatase 2A circuit
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In higher eukaryotic organisms, the checkpoint kinase 1 (Chk1) contributes essential functions to both cell cycle and checkpoint control. Chk1 executes these functions, in part, by targeting the Cdc25A protein phosphatase for ubiquitin-mediated proteolysis. In response to genotoxic stress, Chk1 is phosphorylated on serines 317 (S317) and 345 (S345) by the ataxia-telangiectasia-related (ATR) protein kinase. Phosphorylation of Chk1 on these C-terminal serine residues is used as an indicator of Chk1 activation in vivo. Here, we report that inhibition of Chk1 kinase activity paradoxically leads to the accumulation of S317- and S345-phosphorylated Chk1 in vivo and that ATR catalyzes Chk1 phosphorylation under these conditions. We demonstrate that Chk1 phosphorylation by ATR is antagonized by protein phosphatase 2A (PP2A). Importantly, dephosphorylation of Chk1 by PP2A is regulated, in part, by the kinase activity of Chk1. We propose that the ATR-Chk1-PP2A regulatory circuit functions to keep Chk1 in a low-activity state during an unperturbed cell division cycle but at the same time keeps Chk1 primed to respond rapidly in the event that cells encounter genotoxic stress. 相似文献
993.
Ryan C Zaitsev V Tindal DJ Dyason JC Thomson RJ Alymova I Portner A von Itzstein M Taylor G 《Glycoconjugate journal》2006,23(1-2):135-141
Viruses of the Paramyxoviridae family are the leading cause of respiratory disease in children. The human parainfluenza viruses (hPIV) are members of the
Paramyxovirinae subfamily, which also includes mumps virus, Newcastle disease virus (NDV), Sendai virus (SV) and simian type 5 virus (SV5).
On the surface of these viruses is the glycoprotein hemagglutinin-neuraminidase (HN), which is responsible for cell attachment,
promotion of fusion and release of progeny virions. This multifunctional nature of HN makes it an attractive target for the
development of inhibitors as a treatment for childhood respiratory diseases. Here we report the crystal structure of NDV HN
in complex with a derivative of 2-deoxy-2,3-dehydro-N-acetylneuraminic acid, Neu5Ac2en, that has a functional group designed to occupy a large conserved binding pocket around
the active site. The purpose of this study was to examine the effect of a bulky hydrophobic group at the O4 position of Neu5Ac2en,
given the hydrophobic nature of the binding pocket. This derivative, with a benzyl group added to the O4 position of Neu5Ac2en,
has an IC50 of ∼10 μM in a neuraminidase assay against hPIV3 HN. The IC50 value of the parent compound, Neu5Ac2en, in the same assay is ∼25 μM. These results highlight the striking difference between
the influenza neuraminidase and paramyxovirus HN active sites, and provide a platform for the development of improved HN inhibitors. 相似文献
994.
To date, most studies of nest site selection have failed to take into account more than one source of nest loss (or have combined
all sources in one analysis) when examining nest site characteristics, leaving us with an incomplete understanding of the
potential trade-offs that individuals may face when selecting a nest site. Our objectives were to determine whether northern
flickers (Colaptes auratus) may experience a trade-off in nest site selection in response to mammalian nest predation and nest loss to a cavity nest
competitor (European starling, Sturnus vulgaris). We also document within-season temporal patterns of these two sources of nest loss with the hypothesis that flickers may
also be constrained in the timing of reproduction under both predatory and competitive influence. Mammalian predators frequently
depredated flicker nests that were: lower to the ground, less concealed by vegetation around the cavity entrance and at the
base of the nest tree, closer to coniferous forest edges and in forest clumps with a high percentage of conifer content. Proximity
to coniferous edges or coniferous trees increased the probability of nest predation, but nests near conifers were less likely
to be lost to starlings. Flickers may thus face a trade-off in nest site selection with respect to safety from predators or
competitors. Models suggested that peaks of nest predation and nest loss to eviction occurred at the same time, although a
competing model suggested that the peak of nest loss to starlings occurred 5 days earlier than the peak of mammalian predation.
Differences in peaks of mammalian predation and loss to starlings may constrain any adjustment in clutch initiation date by
flickers to avoid one source of nest loss. 相似文献
995.
Using behavioural and state variables to identify proximate causes of population change in a seabird
Changes in animal population size are driven by the interactions between intrinsic processes and extrinsic forces, and identifying
the proximate mechanisms behind population change remains a fundamental question in ecology. Here we report on how measuring
behavioural and state proxies of food availability among populations experiencing different growth rates can be used to rapidly
identify proximate drivers of population trends. In recent decades, the Cape gannet Morus capensis has shown a major distributional shift with historically large colonies in Namibia decreasing rapidly, whilst numbers at
South African colonies have increased, suggesting contrasting environmental conditions in the two regions. We compared per
capita growth rates of five of the six extant colonies with foraging range (using miniaturised Global Positioning System loggers),
foraging work rate, food delivery rates and body condition of breeding adults. We found significant associations between the
rate of population change, individual behaviour, energetic gain and body condition that indicate that recent population changes
are associated with extrinsic effects. This study shows that behavioural and state data can be used to identify important
drivers of population change, and their cost-effectiveness ensures that they are an appealing option for measuring the health
of animal populations in numerous situations. 相似文献
996.
Jacqueline A. Aitkenhead-Peterson Jess E. Alexander Jana Albrechtová Pavel Krám Barrett Rock Pavel Cudlín Jakub Hruška Zuzana Lhotaková Ryan Huntley Filip Oulehle Tomáš Polák William H. McDowell 《Plant and Soil》2006,283(1-2):187-201
Dissolved organic carbon and nitrogen (DOC and DON) produced in the forest floor are important for ecosystem functions such
as microbial metabolism, pedogenesis and pollutant transport. Past work has shown that both DOC and DON production are related
to litterfall and standing stocks of C and N in the forest floor. This study, conducted in spring, 2003, investigated variation
in forest floor water extractable DOC (WEDOC) and DON (WEDON) and forest floor C and N as a function of lignin, cellulose
and N contained in live canopy foliage across eight Picea abies [L.] Karst stands in northern Bohemia. Based on Near Infrared Spectroscopy (NIR) analysis of foliar materials, lignin:N and
cellulose:N content of the youngest needles (those produced in 2002) were positively and significantly related to WEDOC (R2 = 0.82–0.97; P<0.01) and to forest floor C:N ratio (R = 0.72–0.78; P<0.01). Foliar N was strongly and negatively related to WEDOC and C:N ratio (R = −0.91 and 0.72; P<0.05) among our study sites. WEDON was positively correlated to foliar lignin:N (R = 0.48; P<0.05; n=40). Forest floor C pools were not positively correlated with foliar lignin and cellulose and forest floor N pools were not
positively correlated with foliar N. Instead, a significant negative correlation was found between forest floor N pools and
foliar cellulose (R=−0.41; P<0.05), and between forest floor C pools and foliar N (R = −0.44; P<0.05). From a remote sensing standpoint, our results are important because canopy reflectance properties are primarily influenced
by the most recent foliage, and it was the chemistry of the most recently produced needles that showed a stronger relationship
with forest floor WEDOC and C:N ratio suggesting forest floor production of WEDOC can be calculated regionally with remote
sensing. 相似文献
997.
Ontogenetic changes in the human femur associated with the acquisition of bipedal locomotion, especially the development of the bicondylar angle, have been well documented. The purpose of this study is to quantify changes in the three-dimensional structure of trabecular bone in the human proximal femur in relation to changing functional and external loading patterns with age. High-resolution X-ray computed tomography scan data were collected for 15 juvenile femoral specimens ranging in age from prenatal to approximately nine years of age. Serial slices were collected for the entire proximal femur of each individual with voxel resolutions ranging from 0.017 to 0.046 mm depending on the size of the specimen. Spherical volumes of interest were defined within the proximal femur, and the bone volume fraction, trabecular thickness, trabecular number, and fabric anisotropy were calculated in three dimensions. Bone volume fraction, trabecular number, and degree of anisotropy decrease between the age of 6 months and 12 months, with the lowest values for these parameters occurring in individuals near 12 months of age. By age 2-3 years, the bone volume, thickness, and degree of anisotropy increase slightly, and regions in the femoral neck become more anisotropic corresponding to the thickening of the inferior cortical bone of the neck. These results suggest that trabecular structure in the proximal femur reflects the shift in external loading patterns associated with the initiation of unassisted walking in infants. 相似文献
998.
A total of 430 avian-derived fecal specimens were randomly collected from selected Western Australian commercial aviaries, poultry farms, hatcheries, wildlife parks, and the Perth Zoo and screened for the presence of Cryptosporidium by PCR. Of these, 27 Cryptosporidium-positive isolates were detected, characterized, and compared with 11 avian-derived isolates from the Czech Republic at the 18S rRNA and actin gene loci. Sequence and phylogenetic analysis identified four genetically distinct genotypes, avian genotypes I to IV, from various avian hosts. In addition, the host range for Cryptosporidium galli was extended. Cryptosporidium muris and Cryptosporidium andersoni were also identified in a tawny frogmouth and a quail-crested wood partridge, respectively. 相似文献
999.
Hollibaugh JT Budinoff C Hollibaugh RA Ransom B Bano N 《Applied and environmental microbiology》2006,72(3):2043-2049
We characterized the arsenate-reducing, sulfide-oxidizing population of Mono Lake, California, by analyzing the distribution and diversity of rrnA, cbbL, and dissimilatory arsenate reductase (arrA) genes in environmental DNA, arsenate-plus sulfide-amended lake water, mixed cultures, and isolates. The arsenate-reducing community was diverse. An organism represented by an rrnA sequence previously retrieved from Mono Lake and affiliated with the Desulfobulbaceae (Deltaproteobacteria) appears to be an important member of the arsenate-reducing, sulfide-oxidizing community. Sulfide oxidation coupled with arsenate reduction appears to proceed via a two-electron transfer, resulting in the production of arsenite and an intermediate S compound that is subsequently disproportionated. A realgar-like As/S mineral was formed in some experiments. 相似文献
1000.