摘要:

The ciliary reversal ofParamecium primaureliamating reactive cells was studied using both electrical and chemical stimuli. In an electric field, mating type II cells move towards the cathode at a higher speed rate than mating type I cells. This allowed us to assume that the cathode ciliary reversal is weaker in mating type II than in mating type I cells and, therefore, that a higher influx of Ca2+across ciliary membrane occurs in mating type II cells. Experiments with K+supported this view by showing that ciliary reversal is longer in mating type I than in mating type II cells. Moreover, the threshold values for ciliary reversal induced by electrical and chemical stimuli were shown to be different in the two mating types.

ISSN:0373-4137    

DOI:10.1080/11250009509356042

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Gross morphometric parameters in the Mediterranean gorgonianParamuricea clavatahave been considered with an aim to describe their intraspecific relationships. Bertalanffian growth curves have been calculated, as well as regression equations between parameters. Basal diameter proved to be the best parameter for describing growth of the species.

ISSN:0373-4137    

DOI:10.1080/11250009509356043

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A study is reported of a yellow‐legged gull (Larus cachinnans michaellis)colony located on a flat island in the lagoon of Venice, Italy. Nests and dead chicks, presumably killed by non parental adults, have been recorded and mapped in the same area in three different years. A density index, obtained by summing the squared reciprocals of the distances of each nest from all the others was used, to show the heterogeneity of nest distribution in the colony. By subdividing the colony into quadrats of a size (10 000 m2) that maximizes the variation in average nest number per quadrat, it is seen that the number of killed chicks/nests/quadrat increases with local nest density.

ISSN:0373-4137    

DOI:10.1080/11250009509356044

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Twelve series of releases performed with first flight pigeons reared in four Italian lofts are reported. The presence of preferred compass directions (PCDs) in the initial orientation of the birds is clearly evident, even if less pronounced than in other countries. Young birds show initial bearings which are less homeward oriented and more polarized towards a PCD than do older pigeons.

ISSN:0373-4137    

DOI:10.1080/11250009509356045

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

In a small marine cave of the Oman coasts in the Gulf of Oman a species new for science,Tethya omanensis(Porifera, Demospongiae), has been found. The cave, Tiwi Sink Hole, shows very peculiar hydrological parameters such as low salinity, high temperature and lack of hydrodynamism. Asomanensisis distinguished in the genusTethyaby uncommon spicular characters, it was suggested that these traits represent a special adaptation of the species to its habitat.

ISSN:0373-4137    

DOI:10.1080/11250009509356046

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Abrochtha intermedia(de Beauchamp, 1909) is a bdelloid rotifer belonging to the Philodinavidae family. This species has not been recorded since its discovery and original description in 1909. In this paper we redescribe this rotifer. Scanning electron microscopy revealed its unique rotatory apparatus that is hitherto unknown. Unlike that of other bdelloids its corona consists of a ciliated band limited by a preoral ciliation, an undivided trochus, and by a postoral ciliation, the cingulum. Other morphological characters, such as the rostrum, the dorsal antenna and the foot with spurs and toes, are common to all bdelloids. Some observations ofA. intermediafeeding and swimming behaviour are given.

ISSN:0373-4137    

DOI:10.1080/11250009509356047

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

ISSN:0373-4137    

DOI:10.1080/11250009509356048

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The present paper contends that multiple influences, particularly hermetic‐neoplatonic‐lullian, shaped a widespread attitude towards systematic categories which still largely influences the systematic debate. This also influences the common craving for regularities in evolutionary events which has bedevilled evolutionary studies and systematics. It is argued, instead, that a truly darwinian systematics should be built on purely empirical appreciation of predominantly random events.

ISSN:0373-4137    

DOI:10.1080/11250009509356049

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A theoretical approach to the problem of speciation is developed starting from Lovelock's Gaia hypothesis. In this hypothesis the metaphor of the Biosphereas‐aorganism is present. Developing the metaphor implies that evolution is the way the Biosphere maintains dynamic homeostasis, and speciation has the adaptive value of an increase of biological diversity. An experimental analysis carried out on speciation in the Savi pine vole suggests that the speciation event is connected with heterochromatin amplification in sex chromosomes of these incipient species. Do gene amplifications have adaptive value? A working hypothesis where amplification is a way to start the speciation process, and where speciation has the adaptive value of increasing diversity, is proposed.

ISSN:0373-4137    

DOI:10.1080/11250009509356050

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

General biological and phylogenetic species concepts are compared and contrasted. They are applied to studies on insect herbivores and particularly to variation in populations of the planthop‐persNilaparvata lugensandN. bakeriin Asia and Australia. Speciation processes for these herbivores are discussed in the light of contrasting species concepts. Emphasis is placed on the evolution of reproductive isolation.

ISSN:0373-4137    

DOI:10.1080/11250009509356051

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor