摘要:

In the compound ascidianBotryllus schlosseri, phagocytes change their morphology and frequency during the colonial blastogenic cycle. In the regression phase, characterized by intense phagocytosis, zooids of the old generation are progressively resorbed, the frequency of hyaline amoebocytes falls abruptly, and the frequency of macrophage‐like cells increases significantly. Moreover, the hyaline amoebocytes engulf foreign materials, withdraw their cytoplasmic projections, and change their shape from flat and fusiform to spherical or ovoidal: all these processes suggest that hyaline amoebocytes represent the precursors of macrophage‐like cells. During regression, a significant increase in blood levels of hydrogen peroxide and acid phosphatase is observed, in agreement with data obtained inin vitroexperiments showing an increase in reactive oxygen metabolite production, nitrite ion release, and acid phosphatase secretion associated with phagocytosis.

ISSN:1125-0003    

DOI:10.1080/11250009609356159

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Poeciliidae are a family of viviparous fishes characterized by reversed sexual size dimorphism. Although in all species males are smaller than females, there is a large variability in size dimorphism both between and within species. It has been suggested that variation in the degree of sexual size dimorphism across the family is related to differences in intensity and direction of both intra‐ and intersexual selection. Here the relationship between male body size and in‐trasexual competition, and its effect on male mating success, have been studied in four poeciliid species. Wide interspecific variation was found in the intensity of male‐male competition and in the importance of body size to achieve dominance. InBelonesox belizanusandGirardinus falcatus, larger dominant males almost completely excluded other males from access to the females. Males ofPhalloceros caudimaculatusare less aggressive and dominance influences their access to females to a lesser degree. InHeterandria formosa, aggressive interactions are frequent, but the outcome of fighting and the access to females is not influenced by the size of competitors.

ISSN:1125-0003    

DOI:10.1080/11250009609356160

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Human persecution may have been the major cause of extirpation of the bearded vultureGypaetus barbatusin the western Alps around 1920–1930. However, as shown in a previous work (Mingozzi & Estève, 1996), historical information by itself is insufficient to uphold this hypothesis because the real extent of the shooting pressure endured by the species is not ascertainable. The aim of this paper was to test whether the rapid population decline (30–40 years) shown by historical data is consistent with human persecution. By making assumptions about hypothetical population size and natural survival rates, we tried to assess what rate of additional adult mortality caused by human impact would eventually have led to extirpation. The size of our hypothetical population was estimated by comparison between the current population size (number of breeding pairs) of the golden eagleAquila chrysaetosin the Pyrenees and in the western Alps. All the life‐history parameters available in the recent European literature were used as reference data for a Population Vulnerability Analysis (PVA). A series of computer simulations was performed with R.C. Lacy's programme, VORTEX. Three different scenarios were explored: one without hunting persecution and two with different killing rates. The results suggest that the vulnerability ofG. barbatuswas extremely high and even a moderate rate of killing would have led to extirpation within a very few decades, as suggested by the historical data. Moreover, the species vulnerability shown by the simulations has led to cautious conclusions about the success rate of the current reintroduction project of the bearded vulture in the Alps.

ISSN:1125-0003    

DOI:10.1080/11250009609356161

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

A new species ofAspidisca, Aspidisca terranovaesp. n., was collected from sea ice and sand sediments of Terra Nova Bay (Ross Sea, Antarctica). It is characterized by: seven frontoventral cirri showing a ‘polystyle‐arrangement’, five transverse cirri, a prominent peristomial spur, and a smooth dorsal surface carrying four kineties.

ISSN:1125-0003    

DOI:10.1080/11250009609356162

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The results of a medium‐term survey of cetaceans in the central Tyrrhenian Sea, the first ever all‐year‐round one to be made in the Mediterranean, are reported. Individuals ofBalaenopterasp. were sighted throughout the year, although with significant seasonal differences, in agreement with the hypothesis of a resident population making seasonal migrations around, but remaining inside the Mediterranean Sea. Striped dolphins (Stenella coeruleoalba), the most frequently observed species, are present all year round with no significant seasonal differences. Some observations on the presence and group structure of bottlenose dolphins (Tursiops truncatus) and Cuvier's beaked whale (Ziphius cavirostris) are reported. Individuals of four other species (Physeter macrocephalus, Grampus griseus, Globicephala melaenaandDelphinus delphis) were also sighted.

ISSN:1125-0003    

DOI:10.1080/11250009609356163

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

ISSN:1125-0003    

DOI:10.1080/11250009609356164

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

ISSN:1125-0003    

DOI:10.1080/11250009609356148

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor