摘要:

Summary1. In analysing the ecological conditions of an animal population we have above all to focus our attention upon the most sensitive stages within the life cycle of the animal, that is, the period of breeding and larval development.2. Most animal populations on the sea bottom maintain the qualitatively composition of the species composing them, over long periods of time, though the individual species use quite different modes of reproduction and development. This shows that species producing a large number of eggs have a larger wastage of eggs and larvae than those with only a few eggs. The wastage of eggs in the sea is much larger than on the land and in fresh water.3. In the invertebrate populations on the level sea bottom, large fluctuations in numbers from year to year indicate species with a long pelagic larval life, while a more or less constant occurrence indicates species with a very short pelagic life or a non‐pelagic development.4. In most marine invertebrates which shed their eggs and sperm freely in the water, either(a)the males are the first to spawn, thus stimulating the females to shed their eggs, or(b)an ‘epidemic spawning’ of a whole population takes place within a few hours. Both methods greatly favour the possibility of fertilization of the eggs spawned and show that the heavy wastage of eggs and larvae takes place after fertilization, during the free swimming pelagic life.5. Embryos with a non‐pelagic development may originate(a)from large yolky eggs, in which case all the hatching young of the same species will be at the same stage of development, or(b)from small eggs which during their development feed on nurse eggs, when the individual embryos of the same species may vary enormously in size at the stage of hatching.6. Three types of pelagic larvae are known:(a)Lecithotrophic larvae, originating from large yolky eggs spawned in small numbers by the individual mother animals; they are independent of the plankton as a source of food although growing during pelagic life, are absent from high arctic seas but constitute about 1o% of the species with pelagic larvae in all other seas,(b)The planktotrophic larvae with a long pelagic life, originating from small eggs spawned in huge numbers by the individual mother animal; they feed from, and grow in, the plankton, constituting less than 5% of high arctic bottom invertebrates, 55–65% of the species in boreal seas, and 8o‐85 % of the tropical species, (c) The planktotrophic larvae with a short pelagic life having the same size and organization at the moment of hatching and at the moment of settling; these constitute about 5% of the species in all Recent seas.7. To find out the factors which cause the enormous waste of eggs and larvae, we thus have to study those forms (constituting 7o% of all species of bottom invertebrates in Recent seas) which have a long planktotrophic pelagic life, as only species reproducing in this way have really large numbers of eggs.8. The food requirements of the planktotrophic pelagic larvae are much greater than those of the adult animals at the bottom. The adaptability of the larvae to poor food conditions seems, nevertheless, to be greater than hitherto believed. The significance of starvation seems mainly to be an indirect one: poor food conditions cause slow growth, prolong larval life, and give the enemies a longer interval of time to attack and eat the larvae.9. At the temperatures to which they are normally exposed, northern as well as tropical larvae seem on an average to spend a similar time (about 3 weeks) in the plankton. The length of the pelagic life of the individual species may, however, vary significantly in nature. In the Sound (Denmark) the larvae are never exposed to temperatures outside the range which they are able to endure. The wastage caused by temperature, like that due to starvation, seems mainly to be an indirect one: low temperatures postpone growth and metamorphosis, and give the enemies a longer time to feed on the larvae.1o. When a larva feeding on a pure algal diet metamorphoses into a carnivorous bottom stage, a ‘physiological revolution’ occurs and a huge waste of larvae might be expected. Experiments have, however, shown that this is not the case.11. Young pelagic larvae are photopositive and crowd near the surface; larvae about to metamorphose are photonegative. Larval polychaetes, echinoderms, and presumably also prosobranchs, may prolong their pelagic life for days or weeks until they find a suitable substratum. Forced towards the bottom by their photonegativity and transported by currents over wide bottom areas, testing the substratum at intervals, their chance of finding a suitable place for settling is much better than hitherto believed.12. Continuous currents from the continental shelf towards the open ocean may transport larvae from the coast to the deep sea where they will perish. Such conditions may (for instance in the Gulf of Guinea) deeply influence the composition of the fauna, while in other areas (European western coast, southern California) they seem to be only of small significance.13. The toll levied by enemies appears to be the most essential source of waste among the larvae. A list of such enemies, comprising other pelagic larvae, holoplank‐tonic animals and bottom animals, is given on p. 2o. A medium‐sizedMytilus edulis, filtering 1–4 1. of water per hour, may retain and kill about 100,000 pelagic lamellibranch larvae in 24 hr. during the maximum breeding season in a Danish fjord.14. Species reproducing in a vegetative way, by fission, laceration, budding, etc., might be expected to have good chances of competition in such areas where conditions for sexual reproduction are unfavourable. Nevertheless, they only supply a rather small percentage of the animal populations of all Recent seas, probably because their intensity of reproduction is low and because they are unable to spread to new areas. Most forms reproducing in a vegetative way have sexual reproduction as well.15. Pelagic development is nearly or totally suspended in the deep sea, and is restricted to the shelf faunas. In the arctic and antarctic seas pelagic development is nearly or totally suppressed, even in the shelf faunas, but starting from here the percentage of forms with pelagic larvae gradually increases as we pass into warmer water, reaching its summit on the tropic shelves.16. In order to survive in high arctic areas a planktotrophic, pelagic larva has to complete its development from hatching to metamorphosis within I–I ½ months (i.e. the period during which phytoplankton production takes place) at a temperature below 2–4oC. Most larvae, that is in 95% of the species, are unable to do so and have a non‐pelagic development, but if a pelagic larva is able to develop under these severe conditions the planktotrophic pelagic life seems to afford good opportunities even in the Arctic. Thus the 5 % of arctic invertebrates reproducing in this way comprise several of the species which quantitatively are most common within the area.17. The antarctic shore fauna has poor conditions similar to those of the Arctic. The longest continuous periods of phytoplankton production are 2 and 3 weeks respectively, and pelagic larvae have, in order to survive, to complete their development within this short space of time at a temperature between 1 and 4oC. Accordingly, non‐pelagic development is the rule, but most arctic species are able to support their non‐pelagic development by means of much smaller eggs than the antarctic species, where brood protection and viviparity is dominant. The antarctic fauna has apparently had a longer time to develop its tendency to abandon a pelagic life. The greater the size of the individual born, the smaller its relative food requirements and the better its chance of competing under poor food conditions.18. The relatively few data on reproduction in deep sea invertebrates point to a non‐pelagic development. The larvae of such forms, in order to develop through a planktotrophic pelagic stage, would have to rise by the aid of their own locomotory organs through a water coen with counteracting currents) to the food producing surface layer, and to cover the same distance when descending to metamorphose and settle.19. The ecological features common to the deep sea, the arctic and the antarctic seas, which enable the same animals to live and to reproduce there, contribute to explain the ‘equatorial submergence’ of many arctic and antarctic coastal forms.20. In the tropical coastal zones where the percentage of species with pelagic larvae reaches its maximum, the production of food for the larvae takes place much more continuously than in temperate and arctic seas, because light conditions enable the phytoplankton to assimilate all the year round. The tropical species of marine invertebrates breed (in contrast to temperate and arctic species) within such different seasons that their larval stock, taken as a whole, is more or less equally distributed in the plankton all the year round. This makes the competition in the plankton less keen.21. The fact that a mode of reproduction and development, well fit for an arctic area, is unfit in a temperate or tropical area of the sea is probably one of the main reasons for the restricted distribution of species.22. In most groups of marine invertebrates the individual species have only one mode of reproduction and development, which accordingly restricts their area of distribution. In the polychaetes, however, the individual species often show an astonishing lability in their mode of reproduction and development which enables them to compete in wide areas of the sea. Thus, out of the Western European species of polychaetes, 28‐4% have been found also in the Indian Ocean, and 18%, at least, along the Californian coast, while the corresponding number of Western European echinoderms, prosobranchs and lamellibranchs found also in the Indian Ocean and California amounts to less than 2%.23. The pelagic or non‐pelagic development of marine prosobranchs has proved to be a very fine ‘barometer’ for ecological conditions. Recent observations, still not elaborated, seem to indicate that the shape of the top whorls, the apex, of the adult shells of prosobranchs may show whether the species in question has a pelagic or a non‐pelagic development. This discovery may also give us valuable information about the larval development in fossil species, and help us to form an idea about ecological conditions in sea areas from earlier geolo

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1950.tb00585.x

出版商:Blackwell Publishing Ltd    

年代:1950

数据来源: WILEY

摘要:

Summary1. If it were experimentally possible to examine muscle extracts made during defined phases of the contraction cycle, the relation of muscular work to changes in the composition of such extracts might then be elucidated. The changes of normal muscle proteins in relation to muscular function, could then be considered from a truly physiological point of view.2. Such a study is possible: the technique for making extracts(a)from resting and relaxed muscle, (6) from fatigued muscle, and(c)from contracted muscle, are described. Reasons are given for preferring certain extracting agents. Advantages of the electrophoretic method of analysis are discussed.3. Proteins extractable at μ≪ 0–15 can be assumed to be in solution in the muscle cell. Fatigue and contraction do not modify their qualitative or quantitative distribution in the extracts.4. Proteins appearing in an extract of an ionic strength>0–15 ≪ 0.5 must be assumed to be fixed in the cell as insoluble complexes; they can be released by strong salt solutions, which break down certain linkages. To this group belong actomyosin, β1bT2and γ myosins obtained from normal resting muscle.5. The qualitative and quantitative composition of extracts at μ 0–35‐0‐50 depends on the functional state of the muscle, which influences the protein linkages. Thus, during all kinds of contraction (maximal contraction) or contracture (contracture by monoiodoacetate, strychnine or rigor mortis), β1and β2myosins become inextractible, while a new protein, contractin, appears.6. These results are discussed. It appears that the contractile mechanism is characterized by the formation and dissociation of protein complexes whose constituents are numerous and mostly unidentified, practically nothing is known as to the nature of their linkage forces.7. This review deals with an early stage in the physiological study of muscle proteins: the problem is to determine which of the proteins really belong to the structures which take part in muscular contraction and relaxation–by the use of methods which test the strength of the bonds holding these proteins in position. The use of extracting agents of various ionic composition, which may act selectively on these bonds, may be expected in the future to yield important a

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1950.tb00586.x

出版商:Blackwell Publishing Ltd    

年代:1950

数据来源: WILEY

摘要:

Summary1. The available methods for histochemical analysis of lipoids having been reviewed, the following are regarded as valid for the substances or groups indicated: Sudan black: all liquid or grease‐like lipoids.Nile blue sulphate: ‘acidic’ lipoids (lipines, chromolipoids and free fatty acids) as against ‘neutral’ ones (hydrocarbons, triglycerides, higher alcohols, waxes, steroids, carotenoids, etc.).Fluorescence (without the addition of sulphuric acid): a rapidly fading green is due to vitamin A.Presence of spherocrystals: lipines, cholesteryl esters (and perhaps other sterol esters as well).Osmium tetroxide, primary blackening only: for active unsaturated bonds, most usually ethylenic linkages in fatty acid radicles and probably in carotenoids, but also for aldehyde groups (in plasmal), and for various other strong reducers which are not lipoid.Acid haematein test: phospholipines (possibly acetalphosphatides as well).Feulgen's plasmal test (not the Feulgen‐Verne test): acetalphosphatides by means of the aldehydes liberated from them.Schultz's method I (modification of Liebermann's reaction): cholesteryl group. Schultz's method II (modification of Lifschiitz's reaction):withouta previous oxidation, for certain ill‐defined oxidation products of sterols,witha previous oxidation (by light and air, or by ferric compounds) for the cholesteryl group.Antimony trichloride, and glycerol dichlorhydrin: atransientblue or blue‐green is specific for carotenoids.2. Some of the above tests are subject to interference by certain rare substances; the plasmal test and Schultz's method I may possibly give positive results with certain toad poisons.3. The following tests are rejected as definitely invalid, insufficiently investigated, or superseded by more satisfactory techniques:Fischler's technique for fatty acids;Casanova's reaction;Ciaccio's methods I and II for ‘lipoids’The Smith‐Dietrich method for phospholipines;Romieu's method for lecithin;The Feulgen‐Verne technique for plasmal;Bennett's

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1950.tb00587.x

出版商:Blackwell Publishing Ltd    

年代:1950

数据来源: WILEY

摘要:

Summary1. Enzymes and related substances may be localized in cells either,(a)by separation and analysis of cell parts, or(b)by application of light absorption methods (with or without staining) to living cells or tissue sections.2. Separation of cell parts has been achieved by microdissection, by centrifuga‐tion (sea‐urchin eggs), by sectioning (neurones or centrifugally stratified Amoebae) and by bulk centrifugation of tissue suspensions. Highly sensitive micromethods, based on titration, dilatometry, or manometry, have been evolved for measuring the enzyme content of small fragments of protoplasm.3. Precautions must be taken to minimize separation artefacts. In the bulk centrifugation techniques it is only possible to draw satisfactory conclusions when an enzyme remains associated with certain granules after repeated washing with physiological solutions. Even if an enzyme is constantly associated with, for instance, the mitochondria, it may occur only in certain of them, for they are not necessarily all identical. It is important(a)to distinguish between enzyme activity under the conditions existing in the cell and the maximum activity shown by an extract under optimal conditions,(b)to ensure that the total quantity of enzyme in the fractions separated equals that of the whole cell or tissue,(c)to distinguish between the concentration of, for instance, peptidase in any fraction and the proportion of the total cell peptidase present in the fraction.4. The investigations which have most nearly satisfied these requirements have led to the following conclusions:(a)In various nuclei, dipeptidase, alkaline and acid phosphatase, arginase, uricase and esterase have been detected, all in lower absolute amounts than in the cytoplasm and all except alkaline phosphatase, arginase and uricase in lower concentration. Chromosome‐like threads can be centrifuged from sperm and suspensions of somatic tissues; after removal of desoxyribonucleohistone, there remains a residual chromosome containing ribonucleic acid, alkaline phosphatase and a tryptophane‐containing protein as well as other components,(b)The major part of the cytochrome oxidase, of the succinic dehydrogenase and of several enzymes concerned in fatty acid oxidation and in the Krebs tricarboxylic acid cycle is present in the mitochondria in rat‐liver cells. Mitochondria contain neither dipeptidase nor catalase in sea‐urchin eggs and Amoebae, but in the latter they appear to be associated with amylase activity,(c)Microsomes (cytoplasmic particles 50–200m/j.in diameter) have been found to contain dipeptidase, catalase, phosphatases, ribonuclease, about half the esterase and half the ribonucleic acid in adult liver cells,(d)Much of the catalase, carboxylase and lactic acid dehydrogenase in yeast, of the glycolytic activity in rat liver and of the ribonucleic acid in embryonic tissues and tumours remains in the supernatant after centrifugation for 1–2 hr. at 18,000 g., whether because these substances are freely dissolved in the protoplasm, or because they are eluted from particles during separation is not clear.5. Techniques applied to whole cells or tissue sections involve absorption spectroscopy in visible or ultra‐violet light, fluorescence spectroscopy, colour reactions used as staining methods, digestion techniques which remove cell components of a certain composition, and the utilization of enzyme activity itself to produce, directly or indirectly, a coloured deposit at the enzyme site. Fixation by freezing and drying reduces fixation artefacts and uncertainties in many cases. Particularly useful are semi‐quantitative ultra‐violet absorption methods for nucleic acids and qualitative deposition methods for phosphatases. Methods for localizing nadi‐oxidase, peroxidase, dopa‐oxidase, amine oxidases, riboflavine, thiamine, zymohexase, glucuronidases, lipases and choline esterases have also been described, but some of these, in particular those for the oxidases, are unsatisfactory.6. Desoxyribonucleic acid hardly ever occurs outside the nucleus. During interphase it appears only in the so‐called heterochromatic regions of the chromosomes, but at mitosis the chromosomes become rich in desoxyribonucleic acid throughout their length, and in some cases show alternating bands rich and poor in this substance. After mitosis, the ribonucleoprotein‐rich nucleolus reappears and it has been suggested that, from the nucleolus and its associated chromatin, substances migrate through the nuclear membrane and induce the formation of ribonucleic acid in the cytoplasm. In some egg cells whole nucleolar buds undergo such a migration. After mitosis, the concentration of nucleic acid does, in fact, fall in the nucleus and rise in the cytoplasm, which is especially rich in ribonucleic acid in cells synthesizing protein during growth, regeneration and secretion.7. Information regarding the distribution of phosphatases in cells is considered under three headings:(a)cell‐border phosphatase in sites of rapid solute exchange: gut, kidney and other excretory organs, placental membranes and capillaries;(b)phosphatase in sites of normal and abnormal calcification;(c)phosphatase in sites of active nucleoprotein metabolism.8. Application of nadi‐oxidase, peroxidase and similar techniques suggests that in most, but not all, cases early determination in mosaic eggs is accompanied by regional differences in enzyme content, whereas regulative eggs show a more nearly uniform distribution until a later stage. The techniques involved are often, however, of uncertain validity and this important subject needs reinvestigation.9. Only brief reference is made to plant tissues. In the photosynthetic cells of green leaves, the enzymes concerned in carbon dioxide fixation appear to be situated in the protoplasm outside the chloroplasts, but it is the latter which are concerned with the photolysis of water liberating oxygen and the hydrogen which reduces the initial products of carbon dioxide fixation.10. General conclusions and possible future developments are briefly discussed with special reference to the use of radioactive isotopes and to the need for techniq

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1950.tb00588.x

出版商:Blackwell Publishing Ltd    

年代:1950

数据来源: WILEY