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551.
Feeding in early life stages of the sedentary snail Crepidula is effected both by the use of the radula and by filtering with the gill. The present study is a contribution to the knowledge
of the mechanisms of feeding by early juvenile snails of Crepidula fecunda. Experimental observations were made on specimens of known ages as they were fed constant concentrations of microalgae in
the presence of a primary biological film on a glass substrate. Feeding activity was filmed under the microscope, and images
were digitized for the identification and quantification of feeding structures. A morphological analysis was made of the structures
associated with this process. Results showed that the radula was functional beginning in 1-day-old juveniles, and the gill
functioned in respiration. Gill function in filter-feeding began in juveniles of 9 days old when dorsal and ventral ciliation
had developed, as well as the food pouch. The latter structure begins activity as soon as the gill starts food collection.
Osphradia appeared simultaneous with development of the filter feeding capacity by the gill. In their earliest stages after
metamorphosis, the young snails begin life by radular scraping of primary biofilms, gradually shifting to filter feeding as
the gill developed a critical number of filaments and cilia. 相似文献
552.
Regina?H.?F.?MacedoEmail author Mariana?O.?Cariello Jeff?Graves Hubert?Schwabl 《Behavioral ecology and sociobiology》2004,55(3):213-222
Guira cuckoos, Guira guira, exhibit a rare polygynandrous reproductive system with groups containing several male and female breeders, allowing for important tests of reproductive skew models. Female reproductive strategies involve leaving the group, varying clutch size, egg ejection and infanticide, among others. Here we examined the predictions of reproductive skew models relative to reproductive partitioning among females in groups. We used yolk protein electrophoresis to identify individual females eggs in joint nests. We found that reproductive partitioning favors early-laying females, which lay and incubate more eggs than females that begin laying later. Because the female that lays first tends to switch between repeated nesting bouts, and females do not always contribute eggs to each bout, female reproductive success tends to equalize within groups over time. The pattern of reproductive partitioning differs from that described for anis, another crotophagine joint-nester. We calculated reproductive skew indices for groups in 2 years, for both laying and incubation, as well as an overall population value. These were compared to random skew generated by simulations. Varying degrees of skew were found for different groups, and also across sequential nesting bouts of the same groups. Overall, however, skew did not deviate from random within the population. Nests that reached incubation tended to have lower skew values during the laying phase than nests terminated due to ejection of all eggs followed by desertion. Groups had higher reproductive skew indices in their first nesting bout of the season, and these nests frequently failed. These results illustrate the importance of social organization in determining not only individual, but group success in reproduction, and highlight the flexibility of vertebrate social behavior.Communicated by J. Dickinson 相似文献
553.
Investigations on the influence of pressure on the activity of alkaline phosphatase of some marine invertebrates from the Baltic Sea were carried out at temperatures between 5° and 55°C. The results obtained indicate that the influence of pressure on alkaline phosphatase activity is modified by temperature. At low temperatures, pressure has a decreasing effect on enzyme activity, while it has an increasing effect at higher temperatures. The gill homogenates of the relatively pressure-resistent bivalves Cyprina islandica and Mytilus edulis show a lower decrease of activity under pressure at low temperatures than the gill-homogenate of Carcinus maenas and a purified enzyme preparation of a homoiothermal animal. 相似文献
554.
A Geochemical Survey of Topsoil in the City of Oslo, Norway 总被引:9,自引:0,他引:9
The city of Oslo is situated centrally in the Oslo-graben, which is a Permian rift basin consisting of different kinds of volcanic and sedimentary rocks. In the summer of 1998, approximately 300 samples of surface soil (2–3cm) were taken systematically, 1km–2. The investigated area covers about 500km2. Samples were dissolved in 7M HNO3 and analysed for 29 elements with ICP-AES, mercury with cold-vapour technique (CV-AAS) and arsenic and cadmium with a graphite furnace (GF-AAS). A factor analysis is frequently used to identify relationships among sets of interrelated variables. To describe the covariant relationships among the elements, a factor analysis has been completed. The first factor contains the elements Sc, Fe, Li, Co, Al, Cr, Be, K, Ni, V, Mg, Y, Ba, Zr, Mn and As (listed with decreasing communality). These elements are typical for the minerals in the area and most of these elements have a near normal distribution. Sources for this factor are probably geological. The second factor contains Cd, Hg, P, Zn, Cu, Ba and Pb. They have a log-normal distribution. Road traffic is probably one of the sources contributing to this factor. In Norway studded tyres are used frequently in the winter season which results in large amounts of road dust. Leaded petrol has been a major source for Pb but is not in use any more. Wear and tear of tyres and brakes contribute also to this factor. Other sources contributing to this factor are probably industry, rubbish incineration, crematoria and release of some of these elements from structural material by fire. Factors 3, 4 and 6 with elements such as Ca, Na, La, Ti and Sr probably have geological sources. They are associated with minerals like amphiboles, pyroxenes and feldspars and some of the elements are from sea aerosols. Factor 5 contains Mn, Cd, Zn, As and Pb. Manganese may be derived from many different sources such as rock weathering, windblown dust, agriculture and traffic. Since As and Mn are placed in both factor 1 and 5 they probably have both geological and anthropogenic sources. Concentrations of the elements in the second factor are much higher in the central parts of Oslo, than in the rest of Oslo. The median value of Hg in the centre is 0.48mgkg–1, which is 8 times higher than that in the rest of the city. Also, the other elements have much higher levels in the centre. The industrial district north-east of the centre also has high values. The distribution of arsenic is regular throughout the whole city, but has a slightly higher level in the centre. Norm values for contaminated land used by the Norwegian authorities are 2mg As kg–1 and 25mg Cr kg–1. Of 297 samples, 61% contain more than 25mg Cr kg–1 and 79% more than 3mg As kg–1, which is the detection limit of the analysis. These samples will therefore be regarded as contaminated. Factor analysis places these elements in the geological factor. The Norm value of zinc is 150mgkg–1, and 40% of the samples contain more than this. The Norm value of lead is 150mgkg–1, and 35% of the samples contain. Road traffic is probably the major source for these elements. 相似文献
555.
The marine planktonic diatom Chaetoceros anastomosans, which was isolated from Sagami Bay, was used for a study of resting spore formation mechanisms in batch culture experiments.
Vegetative cells could grow at salinities ranging from 20.7 to 45.5‰, and resting spore formation was enhanced significantly
in nitrate-depleted, high salinity media (40.0 to 45.5‰). The rate of resting spore formation (1.9 d−1) was comparable to the specific growth rate (1.8 d−1) of vegetative cells in the exponential growth phase in normal salinity medium. The size of resting spores formed under high
salinity conditions was smaller than that of spores formed in normal salinity media. Unlike vegetative cells, resting spores
seemed to possess some mechanisms to survive over a wider range of salinities by resisting bacterial attacks on their cell
walls.
Received: 4 August 1996 / Accepted: 27 August 1996 相似文献
556.
Solid waste collection services in Ilorin, Nigeria are shown to be unsatisfactory. The poor service is related to rapid population growth, insufficient data and inconsistent government policies. Surveys have been conducted to assess the quantities and types of solid waste and to show how these, in part, vary according to the nature of the land use and the properties being served. Suggestions for an improved service are offered. 相似文献
557.
Lynne Tolland Jaime G. Cathcart S. O. Denis Russell 《Journal of the American Water Resources Association》1998,34(4):787-794
ABSTRACT. Estimates of peak flows, with specified return periods, are needed in practice for the design of works that affect streams in forested areas. In the province of British Columbia (B.C.), Canada, the new Forest Practices Code specifies the 100-year instantaneous peak flow (Q100) for the design of bridges and culverts for stream crossings under forest roads; and many practitioners are engaged in making such estimates. The state of the art is still quite primitive, very similar to the state of urban hydrology 30 years ago, when popular estimating techniques were used with little consideration given to their applicability. Urban hydrology then evolved on a much more scientific basis, such that within about a 10-year period, standard approaches to design were developed. Forest hydrology should follow the same pattern, at least as far as estimating design flows is concerned. Popular present day design procedures include the rational method and other empirical approaches based on rainfall data, as use of the standard flood frequency approach is limited by the paucity of relevant flow data. Estimating procedures based on peak streamflow measurements and statistics are likely to evolve, and these will include distinctions for rain, snowmelt, and rain on snow floods. Guidelines will also be developed for selecting and applying appropriate procedures for particular areas. 相似文献
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