摘要:

The temporal sequence of eggshell organization (vitelline envelope and chorion) inSilo mediterraneus saturniae(Trichoptera, Goeridae) is highlighted by means of ultrastructural investigation on ovarioles of newly emerged females. Precursors of the vitelline envelope, initially accumulating in the space around egg microvilli, merge together to give rise to a striated border. Discrete striae fuse into the final electron‐dense vitelline envelope. Choriogenesis takes place along the apical region of the follicle cells facing the egg, throughout the progressive release of precursor material synthesized by the follicular epithelium. The onset of chorionic layer deposition is marked by irregular patches which gradually interconnect. As choriogenesis progresses, the follicular epithelium reduces in thickness. An epichorion, with a fibrillar texture, becomes gradually distinct from the follicle cell cytoplasmic matrix and is superimposed on the chorion. At the end of choriogenesis (chorion and epichorion synthesis) the follicular epithelium progressively separates from the egg and folds markedly, giving the chorion a pleated appearance. The synthesis and morphology of the eggshell in 5.mediterraneus saturniaeare compared with those described for other insects laying eggs in water.

ISSN:1125-0003    

DOI:10.1080/11250000009356306

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Anopheles stephensiListon, 1901, is a recognized vector of urban malaria in India. The species occurs in two forms, i.d., the type formA. stephensi stephensi,and the varietyA. stephensi mysorensis.The surface: morphology of the egg ofA. stephensi stephensisensu stricto is described with the aid of optical and scanning electron microscoy. The egg is shiny jet black, ‘skiff‐shaped’ in appearance with its anterior end slightly broader than the posterior one. The average length and width of the egg is 596 ± 8.35 and 196 ± 1.73 (x ± SE) μm, respectively. The number of ridges on the membranous egg‐float varies from 16 to 19. The entire surface of the egg, except the micropyle, is covered with outer chorionic cells which are mostly pentagonal or hexagonal. The tubercles are equispaced. The micropyle is located at the apex of the dorso‐anterior end of the egg, and has a well‐built collar with a minute aperture in the centre.

ISSN:1125-0003    

DOI:10.1080/11250000009356307

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The sexual reproductive cycle of the Tetractinomorpha SpirophoridaCinachyra tarentinawas studied mainly using light microscopy on samples collected in South Italy over a 2‐year period. Some aspects of the egg morphology were observed using transmission electron microscopy. Each year, young oocytes in pre‐vitellogenesis appeared in May and coexisted with growing oocytes. Yolk‐filled eggs were present in June and July. Oogenesis preceded spermatogenesis which occurred only in June.Cinachyra tarentinais an oviparous species having small eggs ranging from 40 to 50 pm in diameter which are scattered in the mesohyl and have a nucleolated nucleus surrounded by dictyosomes of the Golgi apparatus. Growing oocytes and yolk‐filled eggs have an irregular surface because of the presence of numerous pseudopodia which protrude into the mesohyl. Even though apparently gonochoric individuals were mostly observed, the rare specimens with sperm clusters and young oocytes proved the occurrence of successive hermaphroditism as an underlying mechanism. Some aspects of the reproductive biology ofC. tarentinaare compared with that of other Tetractinomorpha.

ISSN:1125-0003    

DOI:10.1080/11250000009356308

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

PCR was used to investigate the genetic differentiation and phylogenetic relationships among five Greek horse breeds at the mitochondrial DNA level. Specifically, a 1350‐bp segment comprising the entire cytochrome b gene of mitochondrial DNA was amplified and subsequently screened for RFLPs. Six out of ten restriction endonucleases were found to detect variability, and nine different haplotypes were observed, all belonging to the same phylogenetic assemblage. Haplotype‐1 was the most common and possessed the highest frequency in all five breeds. The average values of the observed interpopulation and intrapopulation diversity among breeds were similar (mean = 0.30% and 0.27%, respectively). The results obtained contrast with the theory of a separate origin for Greek horse breeds and indicate an extensive admixture among them. This is also the case with the Skyros pony. Finally, the genetic relationships among breeds suggested by mtDNA data were in accordance with RAPD data.

ISSN:1125-0003    

DOI:10.1080/11250000009356309

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Many recent studies have demonstrated that, in monitoring surveys, identification of organisms to the lowest possible taxon may not always be necessary to describe spatial patterns. In this study we examine faunal patterns at different taxonomic levels by means of multivariate analysis. The study site was located in the Bay of Marina Grande (Scilla, Tyrrhenian Sea), in the proximity of an outlet of a drain of domestic sewage. Macrofaunal abundance data from four hard‐bottom stations were analysed at the level of species, genus, family, class, and phylum. Transformation of data was also considered. The gradient of change in community structure was clearly detectable from matrices derived from species, genus, and family abundances constructed using identical transformation. This study, which is the first of this kind on Mediterranean hard‐bottom macrofaunal communities, demonstrated that the taxonomic sufficiency for impact studies is similar to studies in soft‐bottom benthic assemblages, and that identification of organisms to the level of family probably will be acceptable for most monitoring studies.

ISSN:1125-0003    

DOI:10.1080/11250000009356310

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The structure of bat assemblages was studied in relation to variation in forest landscapes in four localities of the eastern Niger Delta (southern Nigeria). The study areas were inhabited by thirteen species, seven Megachiroptera and six Microchiroptera, among whichEidolon helvum, Hypsignathus monstrosus, Rousettus egyptiacus, Saccolaimus peli,andHipposideros cafferwere recorded for the first time, whereasEpomophorus gambianus, Scotonycteris zenkeri, Megaloglossus woermanni, Scotophilus viridis,andMops thersiteswere first cited only recently. The majority of captures occurred in secondary forest habitat (99 specimens belonging to 10 species), followed by primary forest (40 specimens, 5 species), and by the bush (13 specimens, 5 species). A multivariate set of analyses arranged the various species into six ‘ecological groups’: (i)Eidolon helvum, Mops thersites;(ii)Hipposideros caffer,(iii)Hypsignathus monstrosus;(iv)Rousettus egyptiacus, Epomops franqueti, Scotonycteris zenkeri, Nycteris arge,(v)Saccolaimus peli, Scotophilus viridis, Nycteris hispida;(vi)Epomophorus gambianus, Megaloglossus woermanni.The various groups are interpreted in the light of the available information on the ecology and distribution of Nigerian bats.

ISSN:1125-0003    

DOI:10.1080/11250000009356311

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Functional specializations of the right and left side of the brain have been shown to occur in all vertebrate classes and are known to affect various aspects of behaviour. Recent evidence suggests that cerebral lateralization influences cooperative predator inspection in fish. In order to confirm these findings, predator inspection was studied in female guppies (Poecilia reticulata) while a shoalmate (their own mirror image) was visible either on their left or right side. We used laboratory‐reared guppies with no natural experience of predators. One half of the subjects were sensitized to a predator by repeatedly introducing a hungry individual of the speciesLepomis gibbosusinto their home tank prior to the test, while the other half remained without any experience of predators. Guppies with prior experience of the predator showed a greater tendency to approach a live predator when their shoalmate was visible on their right side.

ISSN:1125-0003    

DOI:10.1080/11250000009356312

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

The evolution of megadriles is analysed employing the traditional comparative method supplemented with palaeogeographic information drawn from plate tectonics. The origin of the group is considered in relation to special physiological and developmental strategies which evolved in response to life in compact soil and the acquisition of a larger body size. Further evolution, also related to the terricolous habits, implied differentiations of intestinal structures and modifications of the mating mechanics. The required modifications went on in divergent ways in the three superfamilies Lumbricoidea, Megascolecoidea, and Eudriloidea. The most primitive among the Lumbricoidea, which stemmed from some strain akin to the Haplotaxidae, are limicolous and are distributed over a broad territory corresponding to the northern and central regions of the Lower Triassic Pangaea. Based on ovarian structure, these megadriles may be divided into a northern strain, that originated in Laurasia, and a southern strain, that originated in Gondwana. The geographical range of the main families of Lumbricoidea suggests that they differentiated at a time when the continental masses were separated during the Cretaceous. The most primitive among the Megascolecoidea are the Ocnerodrilidae, which are mostly limnic. Some peculiarities of their sexual apparatus suggest that they might have derived from a strain akin to the Alluroididae. On account of their more advanced adaptations of the copulatory apparatus, the fully terrestrial families Acanthodrilidae and Octochaetidae appear to have derived from some ocnerodrilid ancestor. The geographical range of the Octochaetidae suggests that they evolved in the central region of Triassic Pangaea. The distribution of the Acanthodrilidae supports the hypothesis that they originated in southern and eastern Gondwana and then spread into the western and northern regions, but the taxon is possibly polyphyletic. The Megascoleci‐dae, which are the most diverse family of the group, appear to have stemmed from some ancestor akin to the acanthodrilids following their acquisition of further anatomical and physiological modifications of the copulatory apparatus. Native to Australia and New Zealand, they spread northwards to Indochina and the Asian Far East, as well as to the Pacific coast of North America ‐ possibly during the Cenozoic era. The Eudriloidea, endemic to intertropical Africa, are characterized by the extreme variation of the sexual apparatus, particularly the female structures. They probably took origin from an alluroidid ancestor, but not the same one from which the Megascolecoidea originated. In this superfamily, evolutionary processes seem to have proceeded more rapidly. More generally, the evolution of megadriles is characterized by numerous instances of convergence and remarkably slow speed, but speciation events in Megascolecidae and Eudrilidae were apparently very frequent.

ISSN:1125-0003    

DOI:10.1080/11250000009356313

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

A collection of boring sponges from the Maldives and Seychelles coral reefs was studied. From the etched organogenous material, 16 boring sponge species (belonging to seven genera and five families), were identified; three of these species are new and two are reported for the Indian Ocean for the first time. A list of the boring species hitherto recorded from the area is given. The boring sponge faunas from the Maldives and Seychelles show certain affinities among them and also with that of the entire Indo‐Pacific region.

ISSN:1125-0003    

DOI:10.1080/11250000009356314

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor

摘要:

Echiniscoides sigismundi verrucariaeandE. sigismundi porphyrae,two new subspecies ofEchiniscoides sigismundisensu lato, from the intertidal zone of sub‐Antarctic Macaroni Bay in Marion Island are described. The two subspecies show important peculiarities in cuticle structure, claw number, and male and female gonopores.

ISSN:1125-0003    

DOI:10.1080/11250000009356315

出版商:Taylor & Francis Group    

年代:2000

数据来源: Taylor