摘要:

Both new palaeontological and embryological evidence on chordates require a reassessment of traditional ideas on their early phylogeny and on the evolution of their Bauplan and tissues. A revision of the available data from both palaeontological and zoological points of view is useful both to clarify the better justified possible hypotheses and to point to the more profitable lines of investigation for further advancing our understanding of these problems. Recent advances in the knowledge of the morphology of Cambrian protochordates and of conodonts provide significant evidence for the understanding of the earliest phases of development of typical vertebrate morphology. It appears that, in the oldest lineages related with the evolution of vertebrates, mineralized tissues may have been restricted to the bucco‐pharyngeal region and be of ectodermal and ectomesenchymal origin. The development of dermal and visceral skeletal structures in living vertebrates further supports the overall significance of ectodermal‐ectomesenchymal interactions as the first step towards the origin of the vertebrate skeleton.

ISSN:1125-0003    

DOI:10.1080/11250009909356245

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Two breeds ofBombyx mori, one resistant (Nistari) to BmNPV(Bombyx morinuclear polyhedrosis virus) and the other sensitive (Hosa Mysore), were inoculated with the virus, and changes in the levels of alkalinity and the level of alkaline protease activity were estimated separately at different time intervals. The midgut epithelial cells and fat bodies were also examined at transmission electron microscope at different intervals after inoculation with BmNPV to understand the mode of entry and multiplication of the virus. The alkaline protease activity in the midgut of the tolerant breed showed a sharp increase up to three days after inoculation, which was significantly higher than the increase in the fore‐gut and hindgut and than that of the sensitive breed. The ultra‐structural studies showed that the invasion and multiplication of the virus take place only in the sensitive breed. The study indicated that the tolerance to BmNPV infection is positively correlated with alkaline protease activity, and that the enzyme is more active in the midgut of the tolerant breed.

ISSN:1125-0003    

DOI:10.1080/11250009909356246

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The visual abilities ofZosterisessor ophiocephalus, an ambushing predator inhabiting the intertidal seagrass meadows of lagoons, were studied by morphological and behavioural methods. In its retina, a high number of rods, double and single cones packed in a square mosaic were found, together with the retinomotor response involving the pigment granules and both kinds of photoreceptors. The retinal topography was made by analysing the cone density and density of cells in the ganglion cell layer, and it revealed thearea centralisin the dorso‐temporal region of the retina. No influence of different light intensities (2.4 pimol m‐2s‐1, 0.7 μmol m‐2s‐1and 0.1 μmol m‐2s‐1) on its visual abilities for prey detection was found by comparing the detection and capture efficiencies and the detection and capture distance. A preference for larger food targets was observed. Two capture strategies are described: fast direct and slower hopping capture, the latter exhibited with higher frequency under dim light. Histo‐logical visual acuity was 7’ and behavioural visual acuity was 15’. The morphological and behavioural studies showed thatZ. ophiocephaluscan use vision for feeding in bright and dim light conditions, but it probably feeds more at dusk to avoid predators.

ISSN:1125-0003    

DOI:10.1080/11250009909356247

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Neogastropod snails are gonochorist, i.e. the sexes are separate, but when exposed to tributyltin, a biocide used in marine antifouling paints, the female becomes masculinized, typically developing a penis and a vas deferens. This process is termed ‘imposex’ (describing a superimposition of male sex organs onto the female) and the phenomenon has been recorded in many species world‐wide. Evidence suggests it is caused by an hormonal imbalance induced by tributyltin at a very low ambient concentration of just a few nanograms per litre. Thus, imposex can be used as a highly sensitive bioindicator of tributyltin pollution, especially as the degree of its development appears to be dose‐dependent. In the Mediterranean, onlyHexaplex trunculus(Muricidae) has been studied in this context, but information is limited and the status ofH. trunculuspopulations along the Italian coast remain to be investigated in detail. The present survey is based on examinations of nearly 3000 specimens collected at various localities around Italy. The development of imposex inH. trunculusis described and its ecological implications for the species are discussed.

ISSN:1125-0003    

DOI:10.1080/11250009909356248

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The brittle starAmphiura filiformisis a dominant infaunal species in a silty‐sand community in Galway Bay (west coast of Ireland). The species has been studied since the 1970s at the “Margaretta Station” in Galway Bay, where high‐density populations have been revealed. In previous works at Margaretta Station, recruitment was found to be almost absent, with adults accounting for more than 90% of the populations. The present study shows the occurrence of an annual recruitment in the autumn period, and of a disturbance related recruitment, occurring after a powerful storm. The detection of an annual recruitment might be due to the efficacy of the actual sampling method. Rare events such as heavy storms affect the recruitment pattern, increasing the number of juveniles settling, thanks to a displacement of juveniles which had already settled elsewhere, but then arrived at Margaretta Station by means of a characteristic water circulation system.

ISSN:1125-0003    

DOI:10.1080/11250009909356249

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Spiders are generalist predators, abundant in terrestrial ecosystems, and hence good candidates for interspecific competitive constraints. Contrary to these premises, evidence of interspecific competition in web‐weaving spiders is ambiguous, and new experiments on natural communities are interesting. This paper reports on an experiment designed to test competitive effects in a natural community of web‐weaving spiders, accomplished by selective removal of each of the three locally dominant species:Araneus marmoreus, Argiope bruennichi, andAgelena labyrinthi‐ca.No statistically significant difference was found among control plots and the plots where one of the three species had been removed, for any of the variables measured, but the small number of replicates limited statistic power. Considering only effect direction, and not statistical significance, these removal experiments supported competitive effects on community structure, habitat overlap, and spider body size. On the other hand, effects were contrary to competitive expectations as regards abundance and habitat breadth. These results are in line with the findings of the other removal experiments conducted so far on spiders, that uncovered small intra‐ and interspecific competitive effects for some variables but not for others. So far, there is no evidence that interspecific competition may affect spider communities, although a low‐level competition remains possible, but difficult to test statistically for its evolutionary consequence.

ISSN:1125-0003    

DOI:10.1080/11250009909356250

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Examination of the necessary conditions for parsimony analysis to be a reliable tool in the evaluation of alternative dendrograms shows that such conditions do not obtain in evolutionary events; moreover it is seen that simulations will show that the probability of identifying a correct phylogeny by parsimony analysis of a range of alternative cladograms is practically nil. It can be concluded that parsimony analysis cannot be used in evolutionary studies with any confidence and that, if it is renounced, as it appears necessary, current methods of cladistic analysis (be it framed according to classic hennigian principles or according to pattern cladistics) become unmanageable.

ISSN:1125-0003    

DOI:10.1080/11250009909356251

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Electrophoretic analyses of the tetrameric lactate dehydrogenase isozyme patterns of the endangered cyprinodontid fishAphanius fasciatuswere carried out. Organ and tissue samples of ten individuals of each sex were analysed by cellulose acetate elec‐trophoresis and isoelectric focusing. Isozyme electrophoretic patterns indicated that three LDH loci (Ldh‐A, Ldh‐BandLdh‐C)were active and showed differential tissue expressions. No differences between sexes were observed. TheLdh‐AandLdh‐Bloci were expressed in all tissues analysed, and the A subunits possessed a net negative charge greater than B subunits. Heterote‐tramers including subunit A were not observed, but a complex heterotetramer banding pattern of subunits B and C was detected. On the basis of the staining intensity of the electromorphs,Ldh‐Apredominated in all tissues analysed, with the exception of the liver, whereLdh‐Bpredominated. Instead,Ldh‐Cwas characterised by high relative anodal mobility and was expressed only in the eye. Furthermore, at this locus two alleles were observed in specimens analysed. The LDH banding pattern ofA. fasciatuswas consistent with that of advanced teleosts and it showed an inversion of the net negative charge of products of theLdh‐AandLdh‐Bloci.

ISSN:1125-0003    

DOI:10.1080/11250009909356252

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

The relationships between the tropical spongeAnomoianthella lamellaPulitzer‐Finali & Pronzato, 1999 (from Papua‐New Guinea) and its endobionts, the barnacleAcastasp. and the polychaeteHaplosyllis spongicola(Grube, 1855), were analysed using optical and scanning electron microscope techniques. The specimens ofAcastasp. live in the mesohyl, close to the inhalant surface of the sponge, where they reach a mean density of 12.7‐10 cm‐2. Their apical region is delimited by a thin layer of sponge collagen, whereas sponge cells (archeocytes and lophocytes) gather along the rest of the body of the endobiont. While the barnacles adhere to the spongin skeleton network, the polychaetesH. spongicolaare esclusive to the exhalant canals of the sponge aquiferous system, where they reach a mean density of 57 individuals‐cm"2. No evidence of sponge reaction toH. spongicolawas observed. Potential benefits for the barnacle are protection, against predation and mechanical disturbance, and trophic advantages. Conversely, the barnacle may contribute to strengthen the sponge skeletal network. The association with polychaetes can be regarded as a simple commensalism‐parasitism relationship.

ISSN:1125-0003    

DOI:10.1080/11250009909356253

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Twenty‐four macrodasyid and thirteen chaetonotid species of marine Gastrotricha are reported. Two of these species ‐Urodasys apuliensisandU. bucinastylis ‐are new, while the macrodasyid genusCrasiellais reported for the first time in Italy and the Mediterranean basin. Samples were taken at depths varying from 1 to 34 metres. Altogether, the number of species found was relatively high and comparable with the range of fauna found on the major Italian islands. A possible evolution of the reproductive system in the genusUrodasysis briefly discussed.

ISSN:1125-0003    

DOI:10.1080/11250009909356254

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor