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51.
Species of the genus Paradoxostoma Fischer are an important component of marine and estuarine ostracod faunas throughout the world. This revision of the genus in British waters deals with 17 species of which six are described as new. Each species is diagnosed and illustrated in detail, and comments are made on their ecology and distribution. The specialized mouthparts which characterize the genus are illustrated by means of the scanning electron microscope for the first time. A key to the genus is given. 相似文献
52.
Eight isolates of Naegleria australiensis were obtained from a small lake in Tulsa, Oklahoma. The eight strains were isolated during the hot summer months of July through September, when water temperatures ranged from 27 to 33°C. All eight isolates were pathogenic for mice. The mean time to death for mice was 10 days (range 6–13 days). This pathogenic free-living ameba has not before been reported from the United States or the Western Hemisphere. 相似文献
53.
'Anemotactic' flight paths of tsetse flies in relation to host odour: a preliminary video study in nature of the response to loss of odour 总被引:1,自引:0,他引:1
ABSTRACT. Free-flying, wild Glossina pallidipes Aust. and G. morsitans Westw. were video-recorded in the field in Zimbabwe as they flew out of air permeated with host odour (camera 2.5 m up, looking down at the ground). Analysis of the flight tracks supports the proposal of Bursell (1984) that tsetse flies attracted to an invisible source of host odour respond weakly if at all to wind direction while in flight: on losing contact with the odour the flies made a sharp turn that was uncorrelated with wind direction. The size of the turn varied considerably, with a marked discontinuity in the log-survivorship curve at 120° (a fly which had turned through at least 120° was 5 times as likely to stop the turn as a fly which had turned <120°). Over half the flies made turns of >90° (and <2 m diameter) within the 2×2.5 m field of view of the camera. It is suggested that these turns initially served to arrest the upwind progress of the fly, with the size of the turn determining the degree to which the fly backtracked towards where it last detected odour or continues cross-wind. Mean flight speed was c. 5 ms-1 (min. 2.5, max. probably 7ms-1 ). 相似文献
54.
Envelope development in Trachelomonas lefevrei (Deflandre) begins with the production of short, coarse mucilaginous strands, morphologically similar to the mucilage produced by non-enveloped euglenoids. These initial mucilaginous secretions subsequently become impregnated with manganese (Mn) and/or iron (Fe). Continued mucilage secretion and mineralization results in a mature envelope that is characteristic for the species. When these mature envelopes are treated with oxalic acid to remove the Mn and Fe, the envelopes collapse and are composed only of short, coarse mucilaginous strands similar to those present during early stages of development, prior to their mineralization. Brief treatment with 10 mM EDTA renders dark envelopes colorless, and our EM-EDS analyses show that this corresponds to a loss of Mn from the envelope; however, if Fe is present in the envelope, it is unaffected by the brief treatment. The mucilage present during early stages of envelope development and that remaining after complete demineralization is also morphologically similar to the mucilage in the plug at the anterior end of the envelope. 相似文献
55.
JOHN MOYSE 《Zoological Journal of the Linnean Society》1984,80(1):323-336
Limb movements of restrained stage VI nauplii of Lepas pectinata were studied by cine-photography. Outline drawings were made of successive limb positions in both swimming and grooming activity. The antennae appeared to act as leaky paddles performing both propulsion and food gathering. Free-swimming nauplii averaged 120 limb beats min-1 and a speed of c. 4 mm s-1 . Grooming occurred every 7–20 beats.
It was concluded that lack of streamlining favours filtration at the expense of propulsion. The grooming sequence differs from that of balanid nauplii and is one method of transferring food to the vicinity of the mouth, where sorting and rejection take place prior to ingestion. Fine- and coarse-mesh filters presumably exploit different plankton types. The overall behaviour pattern is well-designed for exploitation of scarce food in the oligotrophic conditions of the ocean-surface habitat. 相似文献
It was concluded that lack of streamlining favours filtration at the expense of propulsion. The grooming sequence differs from that of balanid nauplii and is one method of transferring food to the vicinity of the mouth, where sorting and rejection take place prior to ingestion. Fine- and coarse-mesh filters presumably exploit different plankton types. The overall behaviour pattern is well-designed for exploitation of scarce food in the oligotrophic conditions of the ocean-surface habitat. 相似文献
56.
The effect of changes in the environment on lipid metabolismhas been studied in the brown alga, Fucus serratus L. Lightstimulated the incorporation of radioactivity from /{I4C/}acetateinto oleic and, especially, into linoleic acid. The same effectwas caused by lowering the incubation temperature from 15 °Cto 4 °C. Incubations in the presence of Cd + +, Pb + + orZn+ + had no effect on the total uptake of /{14C/}acetate intothe frond tip samples, but lowered the labelling of total lipidsrelative to aqueous-soluble components. However, pre-exposureof the algae to heavy metal cations caused changes in the uptakeof radioactivity but had less effect on the relative labellingof lipids than incubations in the presence of heavy metal cations.Algae collected from sites where the dissolved levels of heavymetals were elevated, showed a decrease in the relative labellingof lipids from /{14C/}acetate. Concentrations of Cd+ +, Pb++ or Zn+ + at 10 x levels found at the collection site had littleeffect on the pattern of fatty acids made by Fucus serratus. Key words: Lipid metabolism, Fucus serratus L., Environmental changes 相似文献
57.
SUMMARY. We describe a model of zooplankton population dynamics that accounts for differences in mortality and physiology among animals of different ages or sizes. The model follows changes in numbers of individuals and changes in individual and egg biomass through time and it expresses mortality and net assimilation as functions of animal size.
We investigated the effect of egg size, age at first reproduction, and size at first reproduction on the per capita growth rates of populations growing under different conditions. In the absence of predation or when exposed to vertebrate predators that prefer large prey, populations achieve maximum growth rates when animals hatch from small eggs and reach maturity quickly at small sizes. Populations exposed to invertebrate predators that concentrate on small animals may increase r in two different ways. One way is for animals to increase juvenile survivorship by hatching from large eggs and by shortening the juvenile period. An alternative strategy is for animals to hatch from small eggs and to postpone maturity until they grow beyond the range of sizes available to their predators. Certain life history strategies maximize r if animals continue to grow after they reach maturity. By growing larger, non-primiparous females are able to hatch larger clutches and thereby increase the overall rate of population growth.
The model analysis shows how to assess age-dependent mortality rates from field data. The net rate of population increase and the age distribution of eggs together provide specific, quantitative information about mortality. 相似文献
We investigated the effect of egg size, age at first reproduction, and size at first reproduction on the per capita growth rates of populations growing under different conditions. In the absence of predation or when exposed to vertebrate predators that prefer large prey, populations achieve maximum growth rates when animals hatch from small eggs and reach maturity quickly at small sizes. Populations exposed to invertebrate predators that concentrate on small animals may increase r in two different ways. One way is for animals to increase juvenile survivorship by hatching from large eggs and by shortening the juvenile period. An alternative strategy is for animals to hatch from small eggs and to postpone maturity until they grow beyond the range of sizes available to their predators. Certain life history strategies maximize r if animals continue to grow after they reach maturity. By growing larger, non-primiparous females are able to hatch larger clutches and thereby increase the overall rate of population growth.
The model analysis shows how to assess age-dependent mortality rates from field data. The net rate of population increase and the age distribution of eggs together provide specific, quantitative information about mortality. 相似文献
58.
Temperature Regulation of Anthocyanin Accumulation in Apple Skin 总被引:1,自引:0,他引:1
The regulation of anthocyanin accumulation in apple skin (cv.Jonathan) by temperature was studied. In the field the increasein anthocyanin in the skin before harvest coincided with decreasingtemperatures and with increasing ethylene production by thefruit. In detached apples held under continuous white light,the optimum temperatures for anthocyanin accumulation were 12°C in unripe apples and 1624 °C in ripe apples.These effects were explained by corresponding changes in thelevel of phenylalanine ammonia-lyase (PAL), a key enzyme offlavonoid synthesis. PAL levels were higher at low than at hightemperatures and higher in ripe than in unripe apples. In intermittentlight the effects of temperature were similar but levels ofPAL and anthocyanin were lower, particularly in unripe apples.It is concluded that temperature, in conjunction with ripeningand light, is an important factor regulating anthocyanin accumulationand that its effects are mediated by effects on the level ofPAL activity. Key words: Apple, Anthocyanin, Phenylalanine ammonia-lyase 相似文献
59.
SYNOPSIS Cyclic epidermal cellular prohfeiation,with or withoutkeratinization is a vertebrate characteristic Such activityprobably obeys an autonomous rhythm which is legulated throughneuro humoral S)stcms in response to envnonmental (piox imate)stimuliand related to adaptive (ultimate) factors In seeking causeand effect lelationships, however, it becomes apparent thatthe same environmental parameter may be both an ultimate anda pioximate factor, the latter also regulating the rate of lesponseWith regard to molting in homoio'heims, tempeiatuie acts insuch a capacity in many species Peiiodic shedding of the outer epidermis in fish amphibiansand reptiles does not appear to be coirelated with seasonalfactors to the extent that avian and mammalian molts are The evolution of vertebrate molting cycles has amounted to theentraining of inherent epidermal C)cles with seasonal demandsby the organism itself and the environment,these demands actas regulating mechanisms Pieadapted structures such as feathersand hairs function collectively as plumage and pelage in theirvarious roles but separately in their growth and leplacementcycles which, however, are coordinated for maximum functionalefficiency Molting is also synchionized with the seasonal cycleaccording to the availability of energy resources and time tocomplete the essential functions (in addition to molting) Theevolved molting systems as manifested in the gieat variety ofpatterns and types in the vertebrates, may thus be legardedas almost individual responses to selective piessures actingon a umveisil vertebrate chaiacter The basic regulatoiy system involves the neuro hvpophyseal complexwhich contiols target endocrines affecting various functionswhich themselves influence epidermal mitosis and, ultimately,molting 1 he mechanism in its simplest form controls the animalsmetabolism through the thyroid acting independently in a permissivecapacity or synergistically with the adrenal and gonadal hormoneswhich are regulated directly and/or indirectly through negativefeedback 相似文献
60.