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At least 829 records · Page 46Linked to original sources
PubMed1983

Evidence of three major polypeptide species and two major polysaccharide species in the Brucella outer membrane.

Polypeptide and polysaccharide outer membrane components of Brucella abortus 99 (S) were investigated by analysis of cell-wall fractions by sodium dodecyl-sulfate polyacrylamide gel electrophoresis and staining with coomassie blue and periodic acid silver stain. Crude cell-walls were deprived by Triton X-100 treatment of most cytoplasmic material as seen by electron microscopy and cytochrome determination (cell-walls). They were submitted to hot SDS to obtain intentionally after centrifugation, peptidoglycan in the insoluble fraction: SDS-I fractions or peptidoglycan sacculi, and outer membrane components in the SDS soluble fraction as for Enterobacteriaceae. The SDS-soluble fraction contained two major components: a high molecular weight broad band of smooth lipopolysaccharide (S-LPS) and a 43k polypeptide band. The SDS-I fractions were treated by lysozyme to solubilize peptidoglycan before analysis. They contained two major polypeptide groups 36-37-38k, 25-26-27k, a minor one at 31k and variable amounts of high molecular weight S-LPS. The polypeptide and polysaccharide patterns of the entire outer membrane obtained from lysozyme hydrolysed cell-walls are the sum of both SDS soluble and insoluble fraction patterns. These results mean that 25-27k and 36-38k bands are strongly bound to peptidoglycan, probably covalently. The 25-26-27k bands heavily stained for polysaccharides would be glycopolypeptides. In addition, the polysaccharide patterns of S-LPS fraction appears as a high molecular weight broad band, contrary to the multiple regularly spaced bands of high molecular weight E. coli S-LPS. The B. abortus outer membrane is composed of four major components: LPS, 43k and 36-37-38k polypeptides and 25-26-27k glycopeptides.

Brucella abortus↗
PubMed1994

Anti-bacillus substance in the marine sponge, Hyatella species, produced by an associated Vibrio species bacterium.

The bacterial isolate, M22-1, belonging to the genus Vibrio was obtained from an homogenate of the sponge, Hyatella sp. The bacterium was cultured in marine agar and was found to produce an anti-Bacillus compound. The substance was chemically identified as a peptide antibiotic, an andrimid. The same substance was found in the sponge extract, suggesting that the active component was synthesized by the associated microorganism.

Animals↗
PubMed1998

Individuality and the existence of species through time.

The individuality of species provides the basis for linking practical taxonomy with evolutionary and ecological theory. An individual is here defined as a collection of parts (lower-level entities) that are mutually connected. Different types of species individual exist, based on different types of connection between organisms. An interbreeding species is a group of organisms connected by the potential to share common descendants, whereas a genealogical species is integrated by the sharing of common ancestors. Such species definitions serve to set the limits of species at a moment of time and these slices connect through time to form time-extended lineages. This perspective on the nature of individuality has implications that conflict with traditional views of species and lineages: (1) Several types of connections among organisms may serve to individuate species in parallel (species pluralism); (2) each kind of species corresponds to a distinct kind of lineage; (3) although lineage branching is the most obvious criterion to break lineages into diachronic species, it cannot be justified simply by reference to species individuality; (4) species (like other individuals) have fuzzy boundaries; (5) if we wish to retain a species rank, we should focus on either the most- or least-inclusive individual in a nested series; (6) not all organisms will be in any species; and (7) named species taxa are best interpreted as hypotheses of real species. Although species individuality requires significant changes to systematic practice and challenges some preconceptions we may have about the ontology of species, it provides the only sound basis for asserting that species exist independently of human perception.

Phylogeny↗
PubMed2000

Phylogenetic relationships and climatic adaptations in the Drosophila takahashii and montium species subgroups.

We analyze phylogenetic relationships among temperate, subtropical highland, and subtropical lowland species of the Drosophila takahashii and montium species subgroups based on sequence data of COI and Gpdh genes and discuss the evolution of temperate species in these subgroups with reference to their climatic adaptations. In the takahashii subgroup, D. lutescens (the temperate species) branched off first in the tree based on the combined data set, but D. prostipennis (the subtropical highland species) branched off first in the trees based on single genes. Thus, phylogenetic relationships in this subgroup are still ambiguous. In the montium subgroup, the cool-temperate species are phylogenetically close to the warm-temperate species, and these cool- and warm-temperate species form a cluster with the subtropical highland species. This suggests that perhaps the cool-temperate species derived from the warm-temperate species and the warm-temperate species derived from the subtropical highland species. In comparison with the subtropical lowland species, the subtropical highland species may be better able to colonize temperate areas since, as in the temperate species, they have an ability to develop their ovaries at moderately low temperature. However, the subtropical highland species, as well as the subtropical lowland species, were much less cold tolerant than the temperate species. Therefore, considerable genetic reformation would be required for both the subtropical highland and the subtropical lowland species to adapt to temperate climates.

Acclimatization↗
PubMed2006

A mechanistic approach to evaluation of umbrella species as conservation surrogates.

Although species with large area requirements are sometimes used as umbrella species, their general utility as conservation tools is uncertain. We surveyed the species diversity of birds, butterflies, carabids, and forest-floor plants in forest sites across an area (1,600 km2) in which we delineated large breeding home ranges of Northern Goshawk (Accipiter gentilis). We tested whether protection of the home ranges could serve as an effective umbrella to protect sympatric species of the four taxa. We also used an empirical habitat model of occupancy of home range to examine mechanisms by which the Northern Goshawk acts as an umbrella species. Among species richness, abundance, and species composition of the four taxa, only abundance and species composition of birds differed between sites located inside and outside home ranges, which was due to greater abundance of bird species that were prey of Northern Goshawks inside the home ranges. Thus, although home range indicated areas with high abundance of certain bird prey species, it was not effective as an indicator of the species diversity of all four taxa. We also did not find any difference in species richness, abundance, and species composition between sites predicted as occupied and unoccupied using the habitat model. In contrast, when we selected sites on the basis of each habitat variable in the model, habitat variables that selected sites either in agricultural or forested landscapes encompassed sites with high species richness or particular species composition. This result suggests that the low performance of the Northern Goshawk as an umbrella species is due to this species' preference for habitat in both agricultural and forested landscapes. Species that can adjust to changes in habitat conditions may not act as effective umbrella species despite having large home ranges.

Animals↗
PubMed2004

[Dynamics of species diversity in artificial restoration process of subalpine coniferous forest].

Through plot investigation and by adopting the concept of space as a substitute for time, the developments of species diversity of trees, shrubs and herbaceous plants in subalpine coniferous plantations at different restoration stages were studied, and the correlation coefficients of species in each layer were discussed. The results indicated that in the restoration process, the species richness, diversity and evenness in subalpine coniferous plantations were gradually increased in a fluctuating way. The restoration process of Picea asperata plantations showed a tendency of development that in favor of resuming species diversity. The indices of species richness (species number and Margalef index) and species diversity (Shannon-Wiener index and Simpson index) of trees increased rapidly from the early stages of plantation establishment to the stage of canopy closing (about 30 yr of stand age) and then presented a tendency of decrease with some slight fluctuations, while the index of species evenness showed a periodical rising trend. For the shrub layer, the indices of species richness (Simpson index and Macintosh index) gradually increased with increasing restoration years, whereas the indices of species diversity (Shannon-Wiener index) decreased in the early stages, sharply increased during the stages of canopy closing, and then slowly decreased, which exhibited a tendency of high-->low-->high. In the layer of herbaceous plants, the indices of species richness (Margalef index and number of species) and species diversity (Simpson index, Macintosh index and Shannon-Wiener index) presented a trend of decrease in the early stages of plantations establishment to canopy closing and increased later on. During this process, herbaceous species and their life forms changed greatly, with shade tolerant species gradually substituting the intolerant species. Among the plantations of different stand ages, the average correlation coefficients of trees, shrubs and herbaceous species were 41.88%, 50.61% and 37.22%, respectively, indicating that in the 70 years of artificial forest restoration, the continuity and stability of shrub species were the highest, those of herbaceous species showed greatest fluctuation because of the disappearance and regeneration occurred with the alteration of the environmental conditions of plantations, and those of the trees were intermediary.

Altitude↗
PubMed2006

Is abundance a species attribute? An example with haematophagous ectoparasites.

Population density is a fundamental property of a species and yet it varies among populations of the same species. The variation comes from the interplay between intrinsic features of a species that tend to produce repeatable density values across all populations of the same species and extrinsic environmental factors that differ among localities and thus tend to produce spatial variation in density. Is inter-population variation in density too large for density to be considered a true species character? We addressed this question using data on abundance (number of parasites per individual host, i.e. equivalent to density) of fleas ectoparasitic on small mammals. The data included samples of 548 flea populations, representing 145 flea species and obtained from 48 different geographical regions. Abundances of the same flea species on the same host species, but in different regions, were more similar to each other than expected by chance, and varied significantly among flea species, with 46% of the variation among samples accounted by differences between flea species. Thus, estimates of abundance are repeatable within the same flea species. The same repeatability was also observed, but to a lesser extent, across flea genera, tribes and subfamilies. Independently of the identity of the flea species, abundance values recorded on the same host species, or in the same geographical region, also showed significant statistical repeatability, though not nearly as strong as that associated with abundance values from the same flea species. There were also no strong indications that regional differences in abiotic variables were an important determinant of variation in abundance of a given flea species on a given host species. Abundance thus appears to be a true species trait in fleas, although it varies somewhat within bounds set by species-specific life history traits.

Animals↗
PubMed2003

The microhabitat distribution of two Dactylogyrus species parasitizing the gills of the barbel, Barbus barbus.

The microhabitat distribution of two congeneric species Dactylogyrus carpathicus and D. malleus (Monogenea) parasitizing the gills of the barbel (Barbus barbus L.) was investigated. We tested whether congeneric species exhibited microhabitat preference and whether interspecific interactions could be attributed to the microhabitat segregation of congeners. The outlying mean index method was used to evaluate species microhabitats. Gill variables (different microhabitats within gills) were used as environmental factors characterizing the gills. When abundances of both species were highest, and no significant difference was found between the abundance of the two species, the gill segments and gill areas were the most important factors segregating the Dactylogyrus species on the gills. Niche overlap was low within each of the four gill arches, and parasites were segregated in the same microhabitats within each gill arch. When abundances of both species were low, each monogenean species was segregated at the level of the gill arches. When abundances of both species increased, the niche and overlap between species increased. The distribution of both congeneric species confirmed microhabitat preference within the gills. The results suggest that microhabitat preference is dependent on species abundances, species being segregated in the case of low abundance, possibly to increasing mating opportunities. Both niche and overlap between species increased with species abundance. In the case of the high abundance of both species, microhabitat preference seems to be related to interspecific interactions between monogenean species, as previously found for endoparasitic species.

Animals↗
PubMed2002

A comparison of crop and non-crop plants as sensitive indicator species for regulatory testing.

The effectiveness of regulatory non-target plant testing using crop species to predict the phytotoxicicity of herbicides to non-crop species was evaluated for eleven herbicides. These herbicides were representative of eight chemical classes and six modes of action. Data for non-crop plants from pre-emergence and post-emergence efficacy screening studies were compared with those for the most sensitive crop species defined by regulatory tests conducted to meet US EPA requirements. Testing under pre-emergence conditions for ten compounds indicated that for five of the compounds (K-815910, trifluralin, pyridyloxy A, pyridyloxy B and cyanazine), the most sensitive crop species was more sensitive than all the non-crop species evaluated. For metsulfuron-methyl, chlorimuron-ethyl, hexazinone and bromacil, only one of the non-crop species evaluated was more sensitive than the most sensitive crop species from regulatory tests. Data for the tenth compound, chloroacetamide, showed that four of 32 non-crop species tested in efficacy screens had at least one rate at which greater visual effects were observed than were observed for the most sensitive crop response in a regulatory test. The results of post-emergence exposure comparisons for five of the compounds (pyridyloxy A, cloransulam-methyl, chlorimuron-ethyl, cyanazine and hexazinone) indicated that the most sensitive crop species were more sensitive than all the non-crop species evaluated. Data for pyridyloxy B, metsulfuron-methyl and bromacil indicated that only one of the non-crop species evaluated was more sensitive than the most sensitive crop species. For trifluralin, three of the eight non-crop species were more sensitive than the most sensitive crop species. Data for K-815910 indicated that four of the fourteen non-crop species tested were marginally more sensitive than the most sensitive crop, but were within the same range of sensitivity. These results indicate that the current regulatory test batteries and methods using crop species effectively provide suitable sensitive indicator plants for the eleven diverse herbicides evaluated. This comparison indicates that crop species sensitivity to test substances is likely to be representative of non-crop herbaceous species response, regardless of chemical class, mode of action and magnitude or route of exposure.

Crops, Agricultural↗
PubMed1999

Life History Differences between Rare and Common Flowering Plant Species of California and the British Isles.

Generalizations about rare and endangered species are important for the development of conservation management policy and for understanding of the nature of rarity. Therefore, we sought such generalizations by statistically comparing eight life history and reproductive traits of rare and common plant species in two better-studied but climatically and geographically distinct Holarctic floras-those of California and the British Isles. Trends were often similar in both floras. Rare and common species differ significantly for a number of characters. In both floras, a woody habit was significantly more frequent for the rare species than the common species. Also, in both floras, monocarpy was less frequent in the rare species, significantly so in California. The rare species of both floras were, on average, significantly shorter in stature than the common species. This trend in stature remained significant when nonwoody species were compared but did not do so for woody species. Rare and common species differed with regard to their frequency of inflorescence structure types, but these differences were not concordant for both floras. The rare species of the British Isles had significantly higher proportions of mixed and polymorphic flower colors; the trend was not significant in California. In both floras, rare species had a higher frequency of many-seeded fruits, significantly so in California. California's rare species had a significantly higher frequency of dehiscent fruits than common species; the trend was reversed and not significant for the British Isles. We found no significant differences for characters associated with fruit dispersal. Finally, in California, the median altitude of the range of the common species was significantly greater than that of the rare species. At present, these correlates cannot be assigned as possible causes or consequences of rarity. Nonetheless, they may represent "high-risk" traits that could be used to identify other species already at risk or potentially at risk of becoming rarer.

Journal Article↗
PubMed2002

Biosynthesis of triacylglycerol molecular species in an oleaginous fungus, Mortierella ramanniana var. angulispora.

The incorporation of radiolabeled lipid precursors into triacylglycerol (TG) molecular species in Mortierella ramanniana var. angulispora, an oleaginous fungus, was studied to determine the biosynthetic pathways for TG molecular species. Radiolabeled TG molecular species were separated and quantified by reverse-phase high performance liquid chromatography with a radioisotope detector. The major TG molecular species labeled by [1-(14)C]oleic acid at 30 degrees C were OOP, OOO, and OPP (TG molecular species designations represent three constituent acyl groups. G, gamma-linolenic acid; L, linoleic acid; O, oleic acid; S, stearic acid; P, palmitic acid), which were abundant TG molecular species in this fungus. The incorporation of [1-(14)C]oleic acid at 15 degrees C into these molecular species was the same, while that into most other species was decreased, suggesting that biosynthesis of major molecular species such as OOP, OOO, and OPP differs from that of other TG molecular species. [1-(14)C]Linoleic acid incorporation indicated that the major labeled molecular species were LOP and LOO, which may be due to acylation of oleoyl, palmitoyl-glycerol, or dioleoyl-glycerol by exogenous linoleic acid. This is basically the same mechanism as for OOP and OOO biosynthesis from exogenous oleic acid. [(14)C(U)]Glycerol incorporation suggested that TG molecular species containing palmitic acid such as OPP were more readily synthesized through the de novo pathway. Further experiments involving inhibitors such as sodium azide and cerulenin suggested that OOO biosynthesis included a mechanism differing from that in the cases of OOP and OPP. Trifluoperazine, which inhibits the conversion from phosphatidic acid to TG, decreased [1-(14)C]oleic acid incorporation into all molecular species, suggesting that the incorporation into all molecular species included the de novo TG biosynthetic pathway via phosphatidic acid. These results revealed that the biosynthetic pathways for TG molecular species can be classified into several groups, which exhibit different sensitivities to low temperature and inhibitors of lipid metabolism. This implies that the composition of TG molecular species is regulated through different biosynthetic pathways responsible for specific TG molecular species, providing a new insight into the biosynthesis of TG molecular species.

Carbon Radioisotopes↗