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991.
When phylogenetic trees constructed from morphological and molecular evidence disagree (i.e. are incongruent) it has been
suggested that the differences are spurious or that the molecular results should be preferred a priori. Comparing trees can
increase confidence (congruence), or demonstrate that at least one tree is incorrect (incongruence). Statistical analyses
of 181 molecular and 49 morphological trees shows that incongruence is greater between than within the morphological and molecular
partitions, and this difference is significant for the molecular partition. Because the level of incongruence between a pair
of trees gives a minimum bound on how much error is present in the two trees, our results indicate that the level of error
may be underestimated by congruence within partitions. Thus comparisons between morphological and molecular trees are particularly
useful for detecting this incongruence (spurious or otherwise). Molecular trees have higher average congruence than morphological
trees, but the difference is not significant, and both within- and between-partition incongruence is much lower than expected
by chance alone. Our results suggest that both molecular and morphological trees are, in general, useful approximations of
a common underlying phylogeny and thus, when molecules and morphology clash, molecular phylogenies should not be considered
more reliable a priori. 相似文献
992.
Acorn dispersal estimated by radio-tracking 总被引:2,自引:0,他引:2
Bird-dispersed seeds are difficult to track, especially in the case of long-distance dispersal events. To estimate the oak
dispersal distance and the seed shadow generated by the European jay (Garrulus glandarius), we inserted radio-transmitters in 239 acorns, placed them in bird-feeders and then located them by radio-tracking. Using
this methodology we located the exact caching site of 94 Quercus ilex and 54 Q. suber acorns and determined the caching habitat characteristics (vegetation type, distance, spatial distribution). The results
show that: (1) there is no differences in the dispersal distance distribution between the different acorn species or sizes,
(2) dispersal distances range from approximately 3 m up to approximately 550 m (mean = 68.6 m; median = 49.2 m), (3) recently
abandoned fields and forest tracks were the sites preferred by jays to cache acorns, whereas fields and shrublands were avoided
and (4) seed shadows showed acorn aggregation zones (i.e. clusters of caches) close to the feeder as well as isolated caches
at longer distances. The results also suggest that radio-transmitters are a cheap and reliable way to determine seed shadows
and quantify both seed dispersal and post-dispersal seed predation for medium to large seeds. 相似文献
993.
Vincent J. Tepedino Trent R. Toler Brosi A. Bradley Jessica L. Hawk Terry L. Griswold 《Plant Ecology》2007,193(1):59-69
We studied the breeding system and flower visitors of the endangered plant, Penstemon haydenii, at several south-central Wyoming, USA occurrences. In agreement with earlier studies of the species 300 km to the east in
Nebraska, we found Wyoming plants to be self-incompatible and pollinator-dependent for sexual reproduction. Flower visitors
were several species of native bees in the families Apidae (particularly bumblebees), Halictidae (small sweat bees), and Megachilidae
(especially in the genus Osmia); and the masarid wasp Pseudomasaris vespoides. Especially important was Osmia brevis, an abundant megachilid bee, and one of only two species (the sweat bee Lasioglossum (Dialictus) pruinosum was the other) present at all five sites. As in Nebraska, fruit set did not differ between our experimental cross-pollination
treatment and an open-pollinated control. However, unlike Nebraska, open-pollinated treatments in Wyoming produced significantly
fewer seeds per fruit than the experimental out-crossing treatment. We discuss several possible explanations for seed limitation:
(1) a scarcity of pollinators early in the flowering season; (2) resource competition for developing ovules on open-pollinated
inflorescences but not on experimental inflorescences; (3) the deposition of self pollen through intra-inflorescence and intra-genet
pollinator movements; (4) few S-alleles and mating types in the Wyoming metapopulation compared to the Nebraska metapopulation,
from which it likely derives. 相似文献
994.
Claude E. Steck Matthias Bürgi Thomas Coch Peter Duelli 《Biodiversity and Conservation》2007,16(7):2075-2086
The success of the hotspot approach for biodiversity conservation depends on the spatial scale and the indicator species used.
In this study, we investigated grasshopper species richness in Switzerland at a 1 ha resolution including a total of 111 species.
We compared the representativeness of common and of endangered grasshopper species for the overall grasshopper species richness
and we assessed the efficiency of the hotspot approach for grasshopper conservation. The pattern of overall grasshopper species
richness was well represented by both the number of common and the number of endangered grasshopper species. For evaluating
the efficiency of different hotspot approaches for conservation, we compared hotspots of common species, hotspots of endangered
species (rarity hotspots), and hotspots of all grasshopper species (richness hotspots). Among these hotspot types, richness
hotspots not only featured most common grasshopper species, but they even contained more endangered species than the rarity
hotspots. The combination of rarity hotspots and hotspots of common species featured more species than the other combinations
of hotspot types. However, the gain of combining two hotspot types compared to the single-hotspot approach was low (max. 3
species). About 24% of the species were not contained in any of the hotspots. These grasshopper species require species-specific
action plans. As rarity hotspots were located in areas that are rather strongly affected by landscape change, species richness
in rarity hotspots may decrease in the future. We conclude that, for grasshoppers, the hotspot approach on the 1 ha scale
can be an effective way to conserve a high proportion of species richness. 相似文献
995.
An S-adenosylmethionine synthetase gene (metK) from Streptomyces spectabilis was cloned into an expression plasmid under the control of an inducible T7 promoter and introduced into a strain of Escherichia coli (BAP1(pBP130/pBP144)) capable of producing the polyketide product 6-deoxyerythronolide B (6-dEB). The metK coexpression in BAP1(pBP130/pBP144) improved the specific production of 6-dEB from 10.86 to 20.08 mg l−1
. In an effort to probe the reason for this improvement, a series of gene deletion and expression experiments were conducted
based on a metK metabolic pathway that branches between propionyl-CoA (a 6-dEB precursor) and autoinducer compounds. The deletion and expression
studies suggested that the autoinducer pathway had a larger impact on improved 6-dEB biosynthesis. Supporting these results
were experiments demonstrating the positive effect conditioned media (the suspected location of the autoinducer compounds)
had on 6-dEB production. Taken together, the results of this study show an increase in heterologous 6-dEB production concomitant
with heterologous metK gene expression and suggest that the mechanism for this improvement is linked to native autoinducer compounds. 相似文献
996.
Jesús Iván Murillo-Álvarez Gustavo Hernández-Carmona 《Journal of applied phycology》2007,19(5):545-548
The marine waters of the Baja California peninsula (Mexico) are a rich source of brown seaweeds with a great potential for
exploitation. For that reason, Sargassum sinicola, Eisenia arborea, and Macrocystis pyrifera collected from different locations were subjected to extraction of sodium alginate using a pilot-plant scale process developed
in our facilities. The composition and sequence parameters of the recovered alginate were studied by infrared and nuclear
magnetic resonance spectroscopy. The spectral analysis of the products revealed that sodium alginate from S. sinicola contains a greater proportion of guluronate monomers (64%) than that from E. arborea (48%), and M. pyrifera (38%). Computation of the frequencies of diads and triads indicated that the alginate from S. sinicola was constructed by intercalated guluronate-blocks of 14 residues in length. In contrast, the length of the G-block in the
alginates from E. arborea and M. pyrifera were 7 and 4 residues, respectively. The results show that S. sinicola, E. arborea, and M. pyrifera are sources of sodium alginate with different mannuronate/guluronate ratios, as well as a varied building-block length. In
consequence, aqueous dispersions of sodium alginate from the three studied species are expected to exhibit different physical
properties. 相似文献
997.
Kim J Temple KA Jones SA Meredith KN Basko JL Brady MJ 《The Journal of biological chemistry》2007,282(15):11038-11046
The localized activation of circulating glucocorticoids in vivo by the enzyme 11beta-hydroxysteroid dehydrogenase type 1 (11beta-HSD1) plays a critical role in the development of the metabolic syndrome. However, the precise contribution of 11beta-HSD1 in the initiation of adipogenesis by inactive glucocorticoids is not fully understood. 3T3-L1 fibroblasts can be terminally differentiated to mature adipocytes in a glucocorticoid-dependent manner. Both inactive rodent dehydrocorticosterone and human cortisone were able to substitute for the synthetic glucocorticoid dexamethasone in 3T3-L1 adipogenesis, suggesting a potential role for 11beta-HSD1 in these effects. Differentiation of 3T3-L1 cells caused a strong increase in 11beta-HSD1 protein levels, which occurred late in the differentiation protocol. Reduction of 11beta-HSD1 activity in 3T3-L1 fibroblasts, achieved by pharmacological inhibition or adenovirally mediated delivery of short hairpin RNA constructs, specifically blocked the ability of inactive glucocorticoids to drive 3T3-L1 differentiation. However, even modest increases in exogenous 11beta-HSD1 expression in 3T3-L1 fibroblasts, to levels comparable with endogenous 11beta-HSD1 in differentiated 3T3-L1 adipocytes, were sufficient to block adipogenesis. Luciferase reporter assays indicated that overexpressed 11beta-HSD1 was catalyzing the inactivating dehydrogenase reaction, because the ability of both active and inactive glucocorticoids to activate the glucocorticoid receptor were largely suppressed. These results suggest that the temporal regulation of 11beta-HSD1 expression is tightly controlled in 3T3-L1 cells, so as to mediate the initiation of differentiation by inactive glucocorticoids and also to prevent the inhibitory activity of prematurely expressed 11beta-HSD1 during adipogenesis. 相似文献
998.
At the edges of tropical rain forest fragments, altered abiotic and biotic conditions influence the structure and dynamics
of plant communities. In Neotropical rain forests, palms (Arecaceae) are important floristic and ecological elements. Palms’
responses to edge effects appear to be idiosyncratic and to depend on the level of disturbance at edges. This paper explores
how variation in forest structure at the edges of two old-growth forest fragments in a tropical rain forest in western Ecuador
affects palms of different species, life-forms, and size classes. We investigate (1) how edge effects influence the relative
proportion of palm adults and juveniles, (2) how distance from the forest edge affects palm density and species richness,
(3) how altered forest structure along edges affects palm density. We found that at edges (1) palm communities had a lower
proportion of adults relative to juvenile individuals compared to continuous forests, (2) the density of two species of palms
and the overall species richness of the palm community tended to decrease toward the edges within forest fragments, and, (3)
altered forest structure decreased the density of adult palms. Hence, edge effects on palms were controlled by the degree
of modification of the forest structure, and by species responses to edge-related disturbance. 相似文献
999.
Kazuhiro Nakaya 《Ichthyological Research》1988,34(4):431-442
Data on the individual variation and changes with growth in proportions and morphology are presented for the poorly known Apristurus longicephalus, and compared with those of other species. A. longicephalus is concluded to be a distinct species without synonyms, characterized by its long snout, widely separate nostrils, long caudal fin, short abdomen, very sparse teeth, and low number of monospondylous vertebrae. It is a species of small size, maturing at about 42 cm in total length. 相似文献
1000.
Improvement of canine somatic cell nuclear transfer procedure 总被引:4,自引:0,他引:4
Jang G Oh HJ Kim MK Fibrianto YH Hossein MS Kim HJ Kim JJ Hong SG Park JE Kang SK Lee BC 《Theriogenology》2008,69(2):146-154
The purpose of the present study on canine somatic cell nuclear transfer (SCNT) was to evaluate the effects of fusion strength, type of activation, culture media and site of transfer on developmental potential of SCNT embryos. We also examined the potential of enucleated bovine oocytes to serve as cytoplast recipients of canine somatic cells. Firstly, we evaluated the morphological characteristics of in vivo-matured canine oocytes collected by retrograde flushing of the oviducts 72 h after ovulation. Secondly, the effectiveness of three electrical strengths (1.8, 2.3 and 3.3 kV/cm), used twice for 20 micros, on fusion of canine cytoplasts with somatic cells were compared. Then, we compared: (1) chemical versus electrical activation (a) after parthenogenetic activation or (b) after reconstruction of canine oocytes with somatic cells; (2) culture of resulting intergeneric (IG) embryos in either (a) mSOF or (b) TCM-199. The exposure time to 6-DMAP was standardized by using bovine oocytes reconstructed with canine somatic cells. Bovine oocytes were used for SCNT after a 22 h in vitro maturation interval. The fusion rate was significantly higher in the 3.3 kV/cm group than in the 1.8 and 2.3 kV/cm treatment groups. After parthenogenesis or SCNT with chemical activation, 3.4 and 5.8%, respectively, of the embryos developed to the morula stage, as compared to none of the embryos produced using electrical activation. Later developmental stages (8-16 cells) were transferred to the uterine horn of eight recipients, but no pregnancy was detected. However, IG cloned embryos (bovine cytoplast/canine somatic cell) were capable of in vitro blastocyst development. In vitro developmental competence of IG cloned embryos was improved after exposure to 6-DMAP for 4 h as compared to 0, 2 or 6h exposure, although the increase was not significantly different among culture media. In summary, for production of canine SCNT embryos, we recommend fusion at 3.3 kV/cm, chemical activation, culture in mSOF medium and transfer of presumptive zygotes to the oviduct of recipient animals. The feasibility of IG production of cloned canine embryos using bovine cytoplasts as recipient of canine somatic cells was demonstrated. 相似文献