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The dynamics and mechanical forces generated during burrowing in Polyphysia crassa (Annelida: Polychaeta) and Priapulus caudatus (Priapulida) were investigated. Both animals live in soft marine muds and burrow by utilizing a direct peristaltic wave alternating with a high internal pressure event which thrusts the anterior part of the body into the substratum. Forces generated during the various phases of a typical burrowing cycle were measured in animals moving beneath the natural substratum at 5±3 °C using electronic transducers and recorder. During 'head' advance Polyphysia generated 0.027 N, and during 'tail' advance 0.020 N, with peak internal pressures averaging 0.95 kPa (= 0.095 N/cm2 ). Force by Priapulus during head advance and tail advance was 0.081 N and 0.121 N, respectively, with peak internal pressures averaging 2.47 kPa (= 0.247 N/cm2 ). Polyphysia moves more slowly (0.24 cm/min) than does Priapulus (0.76 cm/min) and expends more energy on mass moved per unit distance. These force measurements during a burrowing cycle were used in place of respirometry as a basis for computation of net cost of transport (NCT) for each animal. NCT for Polyphysia was 635 J kg-1 m-1 and for Priapulus was 314Jkg-1 m-l . Cost of transport for all burrowing animals thus far investigated is high compared to swimming, running and flying. For soft-bodied invertebrates that live an entirely buried existence this high cost must be interpreted in the broader context of the adaptive value of infaunal life, especially protection against predation, and not as simply a means of moving about. 相似文献
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An ecological investigation of the Portneuf River, Idaho: a semiarid-land stream subjected to pollution 总被引:2,自引:0,他引:2
The Portneuf River (mean monthly discharge near mouth 1.4-15.4 m3/s) in southeastern Idaho, U.S.A., flows through an area of reduced precipitation (approx. 33 cm/year) and is dependent on underground aquifers and snowmelt runoff from the surrounding mountains for its water. The stream was examined at ten locations, distributed over its 156-km course, during the period 1967-1971. The Portneuf River is shown to have undergone a number of changes from its natural state as evidenced by alterations in water quality and the distribution of benthic invertebrates along the stream course. Of particular interest are changes brought about by the use of the stream for irrigation and by runoff from agricultural lands, factors whose effects are magnified by the semiarid conditions of the region and by poor soil-conservation practices. However, the stream also is affected by wastes from a sewage-treatment plant, phosphate-processing operations, and an assortment of scattered urban sources. Benthic invertebrates were collected during all four seasons by means of artificial substratum samplers and during summer and autumn by a qualitative dip-net technique. In general, the samplers were more effective in obtaining a representative picture ofthe fauna. However, neither procedure alone gave as much information as the combined results. The artificial substratum collections are not believed to be representative of the usual effects of stream devvatering by irrigation withdrawal in as much as the samplers provide refugia for the benthos during the periods of reduced habitat. 相似文献
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Adventitious bud formation on Sitka spruce [ Picca sitchensis (Bong.) Carr.] needle explants was strongly dependent upon the rigidity of the culture medium. In general, of organogenesis was greatest on weak gels and poorest on more rigid gels resulting from increased medium pH or agar strength. There was a significant interaction between agar strength and pH, with the optimum pH for organogenesis declining with increasing agar strength. Poor organogenesis at high agar concentrations was not due to toxic impurities since increased adventitious bud production could be stimulated by decreasing the medium pH whilst maintaining a high agar strength and an agar washing treatment had no significant effect. Although high levels of organogenesis could be sustained on weak gels the resultant adventitious shoots often showed severe vitrification. The frequency of shoots showing vitrification could be reduced by growing the tissues on harder media but this resulted in reduced shoot elongation. Vitrification of needle tissues did not stimulate the formation of adventitious buds in the absence of cytokinins. 相似文献
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ABSTRACT Four new species of the collembolan genus Xenylla, X. convexopyga, X. longistriata, X. dotata and X. marina from Korea are described. X. convexopyga is characterized by an absence of the dorsal seta m3 on Th. II-III. While the other three new species share similarities in dorsal chaetotaxic characters. However, they are dissimilar in the following respects: ventral chaetotaxy, body colour, presence or absence of inner teeth on unguis, the length proportion of abdominal segments and thoracic segments, arrangement of anal papillae and the general shape of apical bulb of fourth antennal segment. As a result of this study, a total of 25 species in 6 genera of Hypogastruridae have been recorded from the Korean Peninsula. 相似文献
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Development of Vacuolar Volume in the Root Tips of Pea 总被引:1,自引:0,他引:1
Cell and vacuole areas were measured by light microscopy inlongitudinal and transverse sections cut at 0.4-mm intervalsalong the apical 7.2 mm of the primary root of pea. The vacuolararea (or volume) fraction that is, vacuole area (orvolume) divided by cell area (or volume) increased fromabout 15 % in cells 0.4 mm from the distal boundary of the apicalmeristem (the cap /root junction), to about 85% in cells situated6.87.2 mm from that boundary. At each distance, vacuoledevelopment tended to be greater in the cortex than in the stele.Vacuoles occupied about 22% of the tissue volume in the first1 mm length of root (measured from the cap/root junction), about31 % of the tissue volume in the first 2 mm, and about 45% whensummed over the apical 5-mm length of root. Phosphorus supplyor deprivation produced only minor and non-significant changesin vacuole development. The results have implications affectingprevious estimates of cytoplasmic and vacuolar phosphate concentrationsin pea root tips. Pisum sativum L., pea, root, vacuole, volume 相似文献
10.
NIKOLAAS J. van der MERWE JULIA A. LEE THORP RICHARD H. V. BELL† 《African Journal of Ecology》1988,26(2):163-172
Stable carbon isotope ratios have been successfully used to assess modern animal diets and to reconstruct prehistoric diets of animals and humans (Vogel & van der Merwe, 1977; van der Merwe & Vogel, 1978; Burleigh & Brothwell, 1978; Vogel, 1978a; DeNiro & Epstein, 1978; Tieszen et al., 1979; Tieszen & Imbamba, 1980; Chisholm, Nelson & Schwarcz, 1982; Tauber, 1981). We have used 13C/12C ratio measurements of bone collagen to study the diets of African elephants in twelve wildlife refuges. These represent most of the habitats in which elephants live, including such diverse plant communities as primary rain forest, savanna woodland and desert. The δ13C values were found to have a simple linear relationship with tree density in most cases. When translated into relative amounts of dietary browse (C3 plants) and graze (C4 plants), the grass content is seen to be systematically under-represented, presumably due to inefficient metabolism. This does not affect the relationship between elephant diet and tree density, which has implications for the study of elephant-woodland interactions, and for reconstructions of past African environments. 相似文献