摘要:

All multicellular organisms ‐ animals, fungi and plants ‐ are derived from unicellular protists which themselves arose from symbiotic associations of various prokaryotes. The position of protists in relation to other living beings and their tremendous genetic diversity is discussed in relation with studies by Sogin and others on comparative sequencing of small subunit ribosomal RNA. Current views on the symbiotic origin of protists and their organelles (nucleus, 9 + 2 flagellum, mitochondria and plastids) are reviewed with particular reference to extant model organisms from phototrophic dinoflagellates and cryptomonads which are examples of ≪eukaryotes within eukaryotes≫. It is emphasised that in addition to mutation and selection, symbiosis is an equally important motor of evolution in general. Protists currently seem to fall into three major groups. The early group seems to lack mitochondria primarily and is represented by the Microspora.Giardia, certain amoeboflagellates, trichomonads and polymastigotes. But recent discovery of mitochondrial chaperons throws some doubts on this view. The second, middle group contains the Euglenozoa (kinetoplastids, euglenoids) and the majority of the former rhizopods. The last one, called crown group, due to a rapid radiation, gave rise to the alveolates (which contain the apicomplexean sporozoans and the dinoflagellates, forming together the sister‐group of the ciliates), the heterokont algae including brown algae, plus oomycetes and net‐slime molds, the cryptomonads, the haptomonads, and the three main branches with multicellular organisms, e.g. plants and animals and true fungi, the latter being the sister group of the animals. Finally, some ideas are developed for a unifying concept of teaching ≪protistology≫ in modern systematic biology. Protists do not form a monophyletic taxon, but exemplify a particular, unicellular organisational level; their classification should avoid any hierarchical categories, but search for true sister‐group relationships.

ISSN:1125-0003    

DOI:10.1080/11250009709356181

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A high decrease in fertility was earlier reported inDugesia polychroaafter induced self‐fertilization. Similar results have now been obtained inPlanaria torvafrom a comparative analysis of cocoon fertility between cross‐ and self‐pairs. The data reported provide further support to the view of ≪inbreeding depression≫ occurring in freshwater planarians.

ISSN:1125-0003    

DOI:10.1080/11250009709356182

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Allozyme structures ofTapes philippinarum, Tapes decussatus, Venerupis aureaandPaphia undulatawere electrophoretically analysed and species similarities established. High rates of polymorphism and significant Hardy‐Weinberg disequilibria were found. InT. decussatusandV. aureahigh levels of both intra‐ and inter‐population genotypic structuring, possibly related to year‐cohort heterogeneities, were ascertained. InT. philippinarumno in‐trapopulation genotypic variance was found, but a high level of an interpopulation genotypic heterogeneity was apparent, as a possible outcome of its introduction in the Adriatic lagoons from different hatchery stocks. Nei's genetic distances were also evaluated and dendrograms obtained. A clear inconsistency emerged between the generic allocation of the taxa and allozyme data, sinceT. philippinarumproved the most dissimilar to the congenericT. decussatus.

ISSN:1125-0003    

DOI:10.1080/11250009709356183

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Mitotic chromosomes of the moray eel,Gymnothorax unicolor, were digestedin situwith Alul, Haelll, Mbol and Ddel restriction endonucleases, and the results were compared with those obtained in the other Mediterranean species of the same family,Muraena helena. Thanks to restriction endonuclease‐ (RE‐) banding technique, it is possible to study the distribution and structure of heterochromatic regions, since subsets of constitutive heterochromatin sensitive/resistant to nuclease action can be observed. From an analysis of the banding patterns it was possible to study the karyotypic structural changes between the two species.

ISSN:1125-0003    

DOI:10.1080/11250009709356184

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Specimens ofLophopus crystallinus, a freshwater bryozoan, were collected from the Lake of Piediluco (Umbria, Italy) at monthly intervals and studied for their protein content and 5'nucleotidase activity. They showed considerable differences in protein content, ranging from 0.2 to 2.5 mg/ml. The activity of non‐specific phosphatase and 5'‐nucleotidase showed a regular decrease which followed in reverse order the increase of protein content. Specimens, collected in December showed the highest protein content and the lowest activities. Furthermore, 5'nucleotidase activity was largely coincident with that of non‐specific phosphatase. In each preparation, alkaline phosphatase activity was higher than acid phosphatase, and the activity of these enzymes decreased in parallel with an increase of protein content. A correlation of 5'nucleotidase activity ofLophopus crystallinuswith its environment was tentatively proposed.

ISSN:1125-0003    

DOI:10.1080/11250009709356185

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The effects of salinity and diet on survival and growth rate of the nereidid polychaetePerinereis rullierihave been investigated under controlled laboratory conditions. The experiment began from nectochaetes at 5–6 setigerous segments to exclude the high mortality occurring immediately after hatching. The tested salinities were 10 ‐20 ‐ 30 and 40%o that slightly exceed those recorded in the natural environment during larval emergence. The larvae were fed with Tetramin MicroMin dry fish food and Tetramin MicroMin added with freeze‐dried lyophilisedUlva rigidato test the possible antistress effect of vitamins C and E, in which the alga is rich. The experimental results highlight the influence of salinity on survival and growth rate ofP. rullieri. Enrichment with alga does not significantly affect survivorship and growth rates under all experimental conditions.

ISSN:1125-0003    

DOI:10.1080/11250009709356186

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The aim of the study was to assess the use of sound level measurement as an index of cicadaCicada orniabundance in Mediterranean coastal habitats, to compare such measurements with indices of larval density at the same sites and to estimate the density of singing males. Sound levels were significantly higher in pinewood than in Mediterranean scrub and were intermediate in olive groves. There was a close correlation between sound level and the number oflarvalskins per tree, which explained 95% of the variation in sound. Measurements of the sound produced by individual cicadas (mean 97.43 dB at 1 cm) allowed an estimate, by computer simulation, of the density of singing males in July. Mean estimates of 9 861 males per hectare in pinewood and 1 618 in olive grove were obtained. The pinewood values were considerably lower than densities of final‐instar larvae, measured in late May, but the discrepancy can be accounted for by larval and adult mortality in the period between the two sets of measurements.

ISSN:1125-0003    

DOI:10.1080/11250009709356187

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Blue‐spotted individuals are found in many populations of the slow worm (Anguis fragilis)throughout Europe. The frequency of occurrence of this colour morph was studied in eight populations from a mountainous territory of northeastern Italy (Tarvisio Forest, Carnic Alps, 750–1600 m a.s.l.). Blue‐spotted individuals were very rare (0.8% of the total sample;n= 744). However, the population inhabiting the town of Tarvisio presented a significantly higher proportion of blue‐spotted individuals than did the other sampled populations. All the blue‐spotted individuals were adult males of large size (average SVL = 173.5 ± 6.8 mm), with heavy body (average body mass = 41 ± 6 g), while the sole blue‐spotted animal captured in Valais was subadult. The presence of blue‐spotted animals within a population was apparently not correlated with habitat type, altitude and latitude, but was positively correlated with increase of longitude from Greenwich (Spearman'sr =0.73,n =8, P = 0.038). A predation experiment with model slow worms demonstrated that the blue‐spotted individuals suffered higher risks of predation than normal coloured ones. Taking into account the result of this experiment, and considering that (1) the frequency of occurrence of the blue‐spotted males within populations was inversely correlated with the proportion of individuals with broken tails (Spearman'sr= ‐ 0.91,n =8, P = 0.002), and that (2) higher frequencies of broken tails may mean higher risks of prédation for natural lizard populations, we conclude that blue‐spotted individuals should be rare in the areas where the density of potential predators is high. It is also suggested that the blue‐spotted colouration may be intrasexually selected for augmenting the individual success of male slow worms in sexual contexts.

ISSN:1125-0003    

DOI:10.1080/11250009709356188

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The paper reports the results obtained over a period of 19 months (June 1992 to December 1993) from the study of the mounting behaviour of a pair of crested porcupines kept in semicaptivity under red light illumination. Forty‐two mounting episodes which occurred inside the artificial burrow were recorded by a videocamera and subsequently analysed to describe the sequence of the mounting and copulation behaviour. The crested porcupine has a rather articulate courtship pattern. In this species, as in the Indian crested porcupine, mounting and copulation occurs throughout the year and appears to be independent of the reproductive status.

ISSN:1125-0003    

DOI:10.1080/11250009709356189

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The methods used to assess a red squirrelSciurus vulgarisreintroduction experiment at Parco Groane, northern Italy, are described. Population size at the removal site was estimated (c. 2400 squirrels) using drey counts, to evaluate the effect of removing animals for reintroduction. Suitability of the release site was investigated in two ways: (1) beforehand, by comparing tree seed abundance with that at the removal site, (2) retrospectively, by comparing drey‐site choice between removal and release site. Increase and dispersion of the reintroduced population were monitored using drey counts and searching for species‐specific feeding signs. Although only eight squirrels could be released (four males, four females), the experiment was successful and by 1996 all wooded habitats at Parco Groane were inhabited by squirrels.

ISSN:1125-0003    

DOI:10.1080/11250009709356190

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor