摘要:

The newtTriturus carnifexis endowed with a mechanism of respiratory compensation which allows the animal to hoard erythrocytes in its spleen and release often large quantities of these into the blood stream, a factor which causes notable variations in all the hematological parameters according to variations in the environmental conditions. The mean arterial pressure, measured at the level of the right aortic arch with a Statham P23 XL transducer, also showed notable variations (from a minimum of about 11 cm to a maximum of about 30 cm of H2O). A statistical analysis of these pressure variations showed a positive correlation to blood volume and negative correlation to spleen volume in groups of 8 chlorbutol‐anaesthetized animals kept at 6°, 12° or 18° C with all their body surface exposed to the air (optimal respiratory condition). In identical groups of animals kept in stagnant water (hypozia‐inducing condition), at the same three temperatures, the spleens appeared empty, and both blood volume and pressure showed constant values, intermediate to those of the animals exposed to the air. Thus, the depletion of the spleen in hypoxia is not due to an increase in pressure; however, this factor seems to control the maximum degree of congestion that the spleen can reach in optimal respiratory conditions.

ISSN:1125-0003    

DOI:10.1080/11250009609356134

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The size and the number of thyroid masses in medium larval, climax, and postmetamorphic developmental stages ofPleurodeles waltlwere examined in histological sections. Morphological data were also obtained from postmetamorphic specimens, that had been treated for a year with thiourea. In addition to a pair of lateral thyroid glands that developed during larval stages, microscopic examination revealed the presence of two or three supernumerary thyroid glands that were very small in the climax stage, but increased appreciably in size and development in 1‐year‐old postmetamorphic animals. Structural modifications in the supernumerary thyroids similar to those observed in the lateral thyroid glands were observed in thiourea‐exposed, postmetamorphic animals. These super numerary thyroids can be classified as one or two thyroid glands located in the anterior medial sagittal region of the lower jaw, and one posterior thyroid gland located in a left parasagktal region near the pericardial sac. On the basis of the thyroid control on body development and growth in the postmetamorphic stage, reported in other studies, including our own, and of the postmetamorphic mor phology of the supernumerary thyroid glands inP. waltl, an evolutive adaptation of the thyroid system to the habitat of this species is hypothesized.

ISSN:1125-0003    

DOI:10.1080/11250009609356135

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

For the construction of their skeleton, several species of Demospongiae utilise foreign material such as sand grains, sponge spicules, diatom oozes and other particles. Even though selection mechanisms were widely debated, no investigation comparing en vironmental sedimentation and particle incorporation had been carried out. The aim of this work is to compare the environmental sedimentation, studied by traps, with the particles found inside the body of the common demosponge,Chondrosia reniformis, collect ed along a depth transect on the vertical rocky cliff of the Portofino Promontory (Ligurian Sea, Italy). The mineralogical analysis eviden ces an active choice regarding the quality of the incorporated matter, with a strong affinity for siliceous particles. The size of the particles incorporated by the sponges at different depths is similar to that of the fine inorganic fraction in the water column. This phenomenon involves two mechanisms: (1) a physical uptake related to the mucous surface of the sponge and (2) the etching action on quartz particles typical ofChondrosia.

ISSN:1125-0003    

DOI:10.1080/11250009609356136

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

AParamuricea clavatapopulation thriving between 29 and 39 m depth on a shoal at the northern entrance to the Strait of Messina (Tyrrhenian Sea) was affected by mucilage coverage at the end of summer 1993. Mucilage became entangled in projecting branches and necrotized the coenenchyme below, leaving the axial skeleton bare. The entire population was heavily affected, extent of injuries being negatively correlated with size of colonies. Colony size, scale and location of damage were related to successful regeneration after six months. Smaller colonies showed a higher mortality, while colonies with over 50–60% of their total branch length damaged were overgrown by invaders and died. The extent of injuries in the central part of the colony was found to be a critical parameter in determining colony regrowth. A number of injured colonies grew during the six months following the disappearance of mucilage, which shows that their regrowth was apparently not influenced by stress due to mucilage.

ISSN:1125-0003    

DOI:10.1080/11250009609356137

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

A population of the Mediterranean gorgonianParamuricea clavatawas heavily damaged by a mucilage coverage of colonies at the end of summer 1993, and suffered a relatively high mortality. Gorgonian population structure before (summer 1992), and two years after (summer 1995) the mucilage event was compared in order to assess the recovery of the population. Despite gorgonian mean density being practically identical on both dates, suggesting that the local population had fully recovered its effectives, the demographic structure of theP. clavatapopulation showed changes from one sampling date to the other. The most striking effect of disturbance due to mucilage was the rejuvenation of the population: in 1995, juveniles constituted 26.1% of the population, while in 1992 they were only 4.2%.

ISSN:1125-0003    

DOI:10.1080/11250009609356138

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Nest‐building behaviour was studied inXylocopa violacea, with particular attention to that exhibited in the construction of each cell, from the formation of the pollen paste to the construction of the diaphragm. Seven inside characteristics of 28 nests excavated in driedArundo donaxcanes were determined. The cell length ranged from 14 to 20 mm. The diaphragms separating the cells were 2 mm thick in the middle, and 4–5 mm at the edge. In 37 additional nests, only data on some characteristics were taken: (a) colour of the pollen paste; (b) cane internode used for nesting.X. violaceais univoltine and solitary, and as in all the otherXylocopaspecies, female average fecundity is very low (7.43 eggs per nest), despite considerable maternal investment. UnivoltineXylocopaspecies are less fertile than multivoltineXylocopaspecies because of the one to three sup plementary generations per year.

ISSN:1125-0003    

DOI:10.1080/11250009609356139

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Female budgerigars that had been given the opportunity to choose their mate laid more promptly, produced a higher number of eggs and reared a higher number of fledgings than females that had been denied the possibility to choose a mate and had been paired at ran dom. In addition, males of self‐selected pairs performed courtship singing at higher rate than those of random pairs. However, in the following brood most differences disappeared as the number of eggs laid and young fledged increased in the random group and the rate of courtship singing decreased in the self‐selected group. It appears, therefore, that choosy females do enjoy a reproductive advantage even though they do not necessarily choose genetically superior males. Male budgerigars singing too little might be simply unable to stimulate ovarian development and sexual response of the female.

ISSN:1125-0003    

DOI:10.1080/11250009609356140

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The reproductive activity of swifts is affected by seasonal fluc tuations of aerial insects which are largely unpredictable, depending day by day on climatic conditions. In this work we investigated whether the parental food provisioning is influenced by hourly fluc tuations of insect abundance or if adults maintain a constant feeding rate. We found during each day that the amount of food delivered to nestlings was not related to hourly insect availability. We also verified that daily insect abundance is related to daily minimum and maximum temperature (38% of variability explained) and is unrelatedtorainfall. Finally we compared, during different reproductive seasons, the aerial insect abundance and the biomass (eggs and nestlings) produced by adult swifts. Insect abundance was constantly high from June to September and did not precisely match the main period of biomass production (first clutch), which reached a maximum in July.

ISSN:1125-0003    

DOI:10.1080/11250009609356141

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Two new species of Tethyidae (Porifera Demospongiae),Halicometes stoneifrom the Andamane Islands andStellitethya murrayifrom the South‐Arabian coast, on material coming from the Natural History Museum of London, are described.H. stoneiis a stalked species characterized by large oxyasters while 5.murrayis encrusting with typical giant megasters, the largest for all the Tethyidae.

ISSN:1125-0003    

DOI:10.1080/11250009609356142

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Investigation of the extensive Italian and European material of the subgenusSigaraprovided definitive evidence thatSigara basalisis a valid species. This taxon, whose neotype has been designated, is described again and its distribution, of an endemic type (Apennines), is established. Comparative observations of the three species ofSigaraliving in the Italian peninsula(S. basalis, S. dorsalis, andS. striata)revealed that the characters useful for specific identification are primarily related with the morphology of the parameres and the 8th dextral abdominal tergite.

ISSN:1125-0003    

DOI:10.1080/11250009609356143

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor