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51.
DANIELA PESSANI RENATA BURRI LAURA SALTON 《Invertebrate reproduction & development.》2013,57(2-3):191-199
Summary Based on the accounts by various authors, an identification key has been constructed for the planktonic zoeae of the 70 species of Mediterranean Brachyura whose larvae are known. The key is based on primary (spines of the carapace, exopodite of the antenna, spines of telson forks) as well as secondary (setation of mouthparts, processes and spines on abdominal somites) morphological characteristics. It allows the identification of the zoeae of 64 species plus those of Liocarcinus genus (six species). 相似文献
52.
LAURA BENITEZ ANA MARTIN-GONZALEZ JUAN C. GUTIERREZ 《The Journal of eukaryotic microbiology》1994,41(4):387-391
ABSTRACT. The application of an immunocytochemical method to identify precystic stages and to analyse the encystment kinetics, by using a polyclonal antiserum against isolated cyst walls from the ciliate Colpoda inflata , is reported for the first time. Three different precystic phases were chosen on the basis of morphological changes and degree of cyst wall formation. By using this procedure a better identification of mature resting cysts with regard to precystic cells or young cysts is provided. An average consensus encystment kinetics of C. inflata , by using an accumulated class frequency analysis, is reported. 相似文献
53.
M. G. HARASEWYCH S. LAURA ADAMKEWICZ MATTHEW PLASSMEYER PATRICK M. GILLEVET 《Zoologica scripta》1998,27(4):361-372
Phylogenetic analyses of partial sequences spanning approximately 450 nucleotides near the 5'end of the 18s rDNA strongly support the monophyly of Apogastropoda and its constituent clades, Caenogastropoda and Heterobranchia. Representatives of the architaenioglossan groups Cyclophoroidea, Ampullariidae and Viviparidae invariably emerge within Caenogastropoda in all analyses. While the Cyclophoroidea and Ampullariidae are monophyletic, the varying position of Viviparidae in all outcomes contradicts its hypothesized sister group relationship with Ampullariidae, and thus the monophyly of Ampullarioidea. Because of the position of Viviparidae, Architaenioglossa does not emerge as a clade in any of our analyses. Campanile consistently emerges between Cyclophoroidea and Cerithioidea, or in a clade with Cyclophoroidea and Ampullariidae, a position not predicted by previous morphological studies. Maximum parsimony analyses of sequence data show Caenogastropoda to comprise a series of sequentially diverging higher taxa. However, maximum likelihood analyses as well as maximum parsimony analyses using only trans-versions divide Caenogastropoda into two clades, one containing the architaenioglossan taxa, Campaniloidea and Cerithioidea, the other containing the higher caenogastropod taxa included in Eucaenogastropoda (Haszprunar, 1988) [= Hypsogastropoda (Ponder & Lindberg 1997)l. Denser taxon sampling revealed insertions to be present in the 18s rDNA gene of several caenogastropod taxa. Earlier reports (Harasewych et al. 1997b) of reduced sequence divergence levels in Caenogastropoda are shown to be restricted to Hypsogastropoda. Based on a broader taxonomic sampling, divergence levels within Caenogastropoda are comparable to those found within Heterobranchia. 相似文献
54.
55.
Effects of mute swan grazing on a keystone macrophyte 总被引:2,自引:0,他引:2
MATTHEW T. O'HARE RICHARD A. STILLMAN JO MCDONNELL LAURA R. WOOD 《Freshwater Biology》2007,52(12):2463-2475
1. This study describes the early summer foraging behaviour of mute swans (Cygnus olor) on the River Frome, a highly productive chalk stream in southern England in which Ranunculus penicillatus pseudofluitans is the dominant macrophyte. 2. A daily maximum of 41 ± 2.5 swans were present along the 1.1 km study reach during the study period (late May to the end of June). The river was the primary feeding habitat. Feeding activity on the river at dawn and dusk was much lower than during daylight, but we cannot rule out the possibility that swans fed during the hours of darkness. 3. The effects of herbivory on R. pseudofluitans biomass and morphology were quantified. Biomass was lower in grazed areas and swans grazed selectively on leaves in preference to stems. A lower proportion of stems from grazed areas possessed intact stem apices and flowering of the plant was reduced in grazed areas. 4. A model, based on the swans’ daily consumption, was used to predict the grazing pressure of swans on R. pseudofluitans. The model accurately predicted the number of bird days supported by the study site, only if grazing was assumed to severely reduce R. pseudofluitans growth. The proportion of the initial R. pseudofluitans biomass consumed by a fixed number of swans was predicted to be greater when the habitat area was smaller, initial R. pseudofluitans biomass was lower and R. pseudofluitans was of lower food value. 5. We concluded that the flux of N and P through the study reach was largely unaffected by swan activity. The quality of R. pseudofluitans mesohabitat (the plant as habitat for invertebrates and fish) was significantly reduced by grazing which also indirectly contributed to reduced roughness (Manning's n) and by inference water depth. Wetted habitat area for fish and invertebrates would also be lowered over the summer period as a consequence of the reduction in water depth. It was estimated that, while grazing, an individual swan may eat the same mass of invertebrates per day as a 300‐g trout. 6. There is a need to manage the conflict between mute swans and the keystone macrophyte, R. pseudofluitans, in chalk streams, and the modelling approach used here offers a potentially useful tool for this purpose. 相似文献
56.
LAURA POLITI EMILIA CHIANCONE LAURA GIANGIACOMO LAURA CERVONI ANNA SCOTTO D’ABUSCO STEFANO SCORSINO ROBERTO SCANDURRA 《Archaea (Vancouver, B.C.)》2009,2(4):221-231
Recombinant amidase from Sulfolobus solfataricus
occurred as a dimer of 110 kDa comprising identical subunits.
Only dimers were present at pHs above 7.0, but with decreasing pH,
dimers associated into octamers, with complete oligomerization
occurring at pH 3.0. Oligomerization showed reversible
temperature-dependence, with octamer formation increasing with
temperature from 36 °C to between 70 and 80° C. Increasing
salt concentrations, favored dissociation of the octamers. Among the
three investigated factors affecting the dimer–octamer
equilibrium, the most important was pH. Among four mutants obtained by
site-specific mutagenesis and selection for pH and temperature
sensitivity, the T319I and D487N mutant amidases, like that of the
native Sulfolobus solfataricus, responded to changes
in pH and temperature with a conformational change affecting the
dimer–octamer equilibrium. The Y41C and L34P mutant amidases
were unaffected by pH and temperature, remaining always in the dimeric
state. The differences among mutants in protein conformation must be
related to the position of the introduced mutation. Although the L34P
and Y41C mutations are located in the helical region 33–48
(LLKLQLESYERLDSLP), which is close to the amino-terminal segment of
the protein, the T319I mutation is located in a strand on the surface
of the protein, which is far from, and opposite to, the amino-terminal
segment. The D487N mutation is located in the center of the protein,
far distant from the 33–48 segment. These observations suggest
that the segment of the protein closest to the amino-terminus plays a
key role in the association of dimers into octamers. 相似文献
57.
MARGRET STEINTHORSDOTTIR KAREN L. BACON MIHAI E. POPA LAURA BOCHNER JENNIFER C. McELWAIN 《Palaeontology》2011,54(4):867-882
Abstract: Bennettites are an abundant and frequently well‐preserved component of many Mesozoic fossil floras, often playing an important ecological role in flood plain vegetation communities. During a recent study focusing on stomatal indices of Triassic–Jurassic fossil plants, it became evident that the leaf fragments of two bennettite genera Anomozamites Schimper (1870) emend. Harris (1969) and Pterophyllum Brongniart (1825) display a significant overlap of leaf shape as well as cuticular characters. Owing to the preference of recognition of single taxa (ideally species) for the stomatal method, we use a database of 70 leaf fragments of Anomozamites and Pterophyllum compressions from five isotaphonomic Late Triassic sedimentary beds of Astartekløft in East Greenland to test whether leaf and cuticle fragments of the two genera can be separated using a range of quantitative and qualitative morphological and statistical analyses. None of the observed characters – including stomatal frequencies – could be applied to separate the fragments of the two genera into well‐defined groups. Our results therefore indicate that fragmented material and dispersed cuticles cannot be utilized to distinguish between Anomozamites or Pterophyllum at the genus level, but that instead these cuticle fragments may be used interchangeably as stomatal proxies. Classification of fossil leaves into either of these genera is thus only possible given adequate preservation of macro‐morphology and is not possible based solely on cuticle morphology. We suggest that this large inter‐ and intra‐generic morphological variation in both leaf and cuticle traits within Anomozamites and Pterophyllum may be related to the bennettites’ role as understory plants, experiencing a range of micro‐environmental conditions, perhaps depending mainly on sun exposure. Based on the results obtained in this study, we conclude that Anomozamites and Pterophyllum cuticle fragments can be employed interchangeably in palaeo [CO2] reconstructions based on the stomatal method, thus potentially annexing a plethora of bennettitalean fossil plant material as CO2 proxies, including dispersed cuticles. 相似文献
58.
Abstract Woodpeckers are considered keystone species for webs of cavity nesters and habitat and resource specialists that strongly depend on availability of trees suitable for cavity excavation. Most studies carried out in northern hemisphere temperate coniferous forests emphasize the importance of old growth stages of forests or large dead trees as habitat for cavity builders. We present a study of Nothofagus pumilio tree selection by the magellanic woodpecker (Campephilus magellanicus) that incorporates dendroecological data on long‐term growth trends of trees that provides new insights into the processes that create suitable habitat for cavity excavating species. We analysed 351 cavity and neighbouring control trees in terms of age and radial growth patterns, as well as external tree characteristics. In addition, from a subsample of these trees we developed tree‐ring chronologies for each group using standard methods in order to analyse potential differences in radial growth patterns between cavity and non‐cavity trees. Multivariate models that account for differences between paired cavities versus control trees indicated that growth decline and the degree of crown dieback were the primary variables explaining magellanic woodpecker tree selection for cavity building. In contrast to previous work, neither diameter (above a certain threshold) nor age, were important determinants of selection. Furthermore, trees that became present cavity are those that had synchronously declined in radial growth during the 1943–44 and 1956–57 droughts and the 1985–86 massive caterpillar defoliation. Insect outbreaks and extreme climatic events may episodically reduce vigour, induce partial crown mortality, trigger increased fungal attack and heart rot formation at different tree heights on the bole in a group of trees and thus increase availability of soft substrate and their likelihood of cavity excavation by the magellanic woodpecker. These results underscore the importance of drought/biotically‐induced canopy dieback events in creating habitat for woodpeckers and their dependent cavity users. 相似文献
59.
60.
Dual role for an allelochemical: (±)-catechin from Centaurea maculosa root exudates regulates conspecific seedling establishment 总被引:4,自引:1,他引:3