摘要:

The sessile macrofauna, in spite of the taxonomic and phylogenetic heterogeneity of its components, may be regarded as an ecological unity with a well characterized role in marine ecosystems. This paper reviews the aspects of sessile macrofauna that have the greatest ecological relevance: the building of a physical structure for the community; the intra‐ and interspecific interactions; the different adaptive strategies and the developmental and morphological plasticity.

ISSN:0373-4137    

DOI:10.1080/11250008609355518

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

This paper concerns a hypothesis on vertebrate sex‐differentiation, which although very familiar to zoologists, is still viewed with caution. The hypothesis is that the onset of gonadic sex‐differentiation depends upon a preliminary discrimination between the developmental powers shown by embryos that belong to a homogametic or to a heterogametic karyotype. Only in the heter‐ogametic‐sex would there occur a precocious ubiquitarian synthesis of a peculiar cell‐surface antigenic protein, that acts as a primary sex‐determining factor able to alternatively direct the organogenesis of either testicular or ovarian structures in developing gonads of vertebrate species endowed respectively with a male and a female heterogamety. In later developmental stages, after the differentiation of the gonadic endocrine glands, the steroid hormone typical of the heterogametic‐sex (testosterone when the heterogametic‐sex is the male, for instance in mammals; or estradiol when the heterogametic‐sex is female, for instance in birds) could induce further synthesis of the same sex‐determining cell‐surface antigenic protein, this time, however, only at the level of the somatic cells of developing gonads. In this way, gonadic sex‐reversals may be obtained by treating precociously homogametic‐sex individuals with the steroid hormone typical of the heterogametic‐sex.

ISSN:0373-4137    

DOI:10.1080/11250008609355519

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

An experiment was performed to investigate the genetic and behavioural mechanisms responsible for the persistance of the vestigial phenotype in a laboratory mixed population ofDrosophila melanogaster. Successive backcrosses between a vestigial and a wild strain, determining modifications of thevg'sgenetic background, produced an increase of its reproductive fitness. Nevertheless, the homogeneity of fitness between the two phenotypes is not sufficient to guarantee the equilibrium in a mixed population. Behavioural factors related to sexual attraction and not to size and shape differences, by promoting heterogeneous matings, induce a decrease of thevgindividuals. In particular, a pheromonal control of mating patterns is thought to function as a recognition mechanism in selective matings.

ISSN:0373-4137    

DOI:10.1080/11250008609355520

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The somatic and meiotic chromosomes ofLemniscomys barbarus, belonging to an isolated Maghreb population, were studied. The karyotype was analysed using and G banding techniques and silver‐staining for the nucleolus organizer regions (NORs) and was found to consist of 54 chromosomes. The constitutive heteroch‐romatin was widely distributed throughout the centromeric regions of numerous autosomes and of the X heterochromosomes, while two pairs of chromosomes displayed NOR bands. Karyotypic differences ascribable to pericentric inversions emerged from a comparison with Matthey's (1954) observations for the same species.

ISSN:0373-4137    

DOI:10.1080/11250008609355521

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Nuclear heterogeneity of Purkinje neurons has been studied cy‐tochemically in five species of reptiles, on the basis of the response of DNA to the Feulgen reaction, and of the distribution area of the Feulgen‐positive material.

ISSN:0373-4137    

DOI:10.1080/11250008609355522

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The present paper reports that in 3‐month‐old red‐legged partridges(Alertons rufa)early experience of certain foods, restricted to the 10 days after hatching, determines some later shifts of preference towards known foods. Vegetable seeds, insect larvae or commercial food dust were the foods used during the treatment period. The increase of preference, measured as grams of food eaten, was independent of the type of food tasted after hatching. The adaptive and applied implications of such a tendency are discussed.

ISSN:0373-4137    

DOI:10.1080/11250008609355523

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

In a non deciduous oak wood near Rome, earth heaps formed over fallen trees and mainly covered by moss and blackberry shrubs are common. These heaps shelter many rodents’ nests. The dominant species captured in the area were the yellow‐necked mouse (Apodemus flavicollis)and the bank vole (Clethrionomys glareolus). A manifest copresence of the two species in the area and particularly in the heaps was observed. The choise of a heap by one species and/or the other does not seem to be influenced by the overhanging vegetation, as indicated by the traps placed on the heaps.

ISSN:0373-4137    

DOI:10.1080/11250008609355524

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Guanylate cyclase activity has been studied biochemically and cytochemically in the testis ofEsox luciusat the time of spermiation. The results of biochemical assays indicate that the specific activity of the soluble form is about three times higher than that of the paniculate form and that Mn++is required for maximal enzyme activity. The cytochemical results demonstrate that the reaction product of guanylate cyclase is localized primarily on the plasma membranes of Sertoli cells and also on myoid and endothelial cells. This distribution of cyclase activity may indicate that this enzyme modulates the transfer of metabolites and hormones from the blood and/or lumen to Sertoli cells andvice versa.

ISSN:0373-4137    

DOI:10.1080/11250008609355525

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

The authors have studied the effects of insulin and glucagon administration on the blood glucose levels of the lizardPodarcis s. siculaRaf. during the winter. The administration of insulin induces hypoglycaemia with the blood glucose levels reaching a minimum after 3 injections of 4 IU of insulin and a subsequent partial recovery during the course of the treatment. Glucagon treatment on the contrary causes a strong hyperglycaemia which is dose‐dependent and reaches the maximum values about 2.30 hours after the administration of the hormone. The hyperglycaemic action of glucagon is evident also in specimens previously treated with insulin. The glucagon action is not long lasting and the blood glucose levels become normal within 24 hours of the administration of glucagon.

ISSN:0373-4137    

DOI:10.1080/11250008609355526

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor

摘要:

Direct effects of gonadotrophin releasing hormone analogs (GnRHa) on gonadal steroidogenesis have been shown, eitherin vitroorin vivo, in male and female mammals, in the granulosa cell of fowls, and in the testis of amphibians.

ISSN:0373-4137    

DOI:10.1080/11250008609355527

出版商:Taylor & Francis Group    

年代:1986

数据来源: Taylor