摘要:

SummaryWhat is presented here is a tentative synthesis of morphological, cytological, physiological and ecological data on planktonic algae, which I hope will help in the understanding of mutual relationships. Emphasis is put on the marine phytoplankton although effort has been made to include the more significant limnological information.(1) All the algal classes, but two, are present in the marine plankton – which makes 13 classes. Many or most of them possess one or several features that are commonly viewed as animal characters, and so Bacillariophyceae (diatoms) are the more typical ‘algae’ in marine plankton. Coincidently or not, they have received much more attention than any other class.(2) Both structurally and morphodynamically, colonies of cells often appear as something else or something more than sums of cells.(3) There is a profuse variety of flagellar types and flagellar appendages, whose functional significance is open to investigation. In general, swimming velocity (ca. 1 m h‐l) exceeds sedimentation rate (ca. 0·7 m day‐1) by one order of magnitude or more.(4) Very few phytoplankters can truly be described as “naked”. Cell coverings fall into eight major categories which differ by chemical composition, structure and ontogeny. An additional, external organic coating may be widespread. Mucus and microfibrils may also be more common than previously thought.(5) The variability of chloroplast morphology and ultrastructure has not been explored for functional relationships.(6) Evidence for the presence of intracellular bacteria and viruses is rapidly increasing.(7) The suspension of algal cells in the medium depends on a number of morphological factors whose effects are often opposite. The sinking rate increases with increasing cell size and is maximum for spheroid (not spherical) shapes; colonies sink faster than the individual cells. The incidence of various shapes, appendages, mucilage and cell orientation is, essentially, intricate and/or insufficiently known. Lipidic inclusions are no longer viewed as floating devices but the ancient theory of ionic exchange has been revived. As now understood, the suspension of phytoplankton is no more a matter of floating, but rather exploring different layers and being tossed around by physical entrainment. However, questions remain the same: how do the “morphological adaptations” contribute to this, and how do different forms compare to each other?(8) As far as the absorption of nutrients is concerned, there is an advantage for phytoplankters to be small and either motile or rapidly sinking. The permeability of the various cell coverings has been ignored. The advantage of being small is confirmed by the consideration that growth rates and all the metabolic rates decrease with increasing size. However, the balance of photosynthesis against respiration for varying sizes is a complex problem.(9) After an extensive review of the literature, the existence of several “shade species” is confirmed (without ensuring that light is the responsible factor). These taxa exhibit the full range of shapes, sizes, structures and behaviour, so that the relevant morphological adaptations, if any, are at least polymorphic.(10) Although grazing certainly moulds the size spectrum and the algological spectrum of phytoplankton to a large extent, the effect of a given morphological feature can hardly be generalized, except that long appendages, mucilages, and probably colonies discourage grazers. The role of bioluminescence and trichocyst expulsion may also be considered.(11) The hope of correlating cell size with a single factor of the environment, whether temperature or something else, should be abandoned since many more factors are involved. On the other hand, multi‐parametric models can justify or predict which cell size predominates under a given set of conditions (note the works of H. J. Semina and co‐workers, T. R. Parsons and M. Takahashi, and E. A. Laws).(12) The ratio of surface area to volume of the cell is a meaningful physiological index. Its relative conservation among the vagaries of sizes and shapes, and its ecological regulation need further investigation.(13) Considering the profusion of data that has accumulated on the structure and functioning of planktonic algae, and realizing that sophisticated techiques are available for both kinds of studies, now is the time, it seems, for fruitful research into the relationships between form and function. Such research will certainly increase our understanding of specific variability

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1982.tb00702.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

Summary1. Several methods of varying accuracy have been used to assess what sounds small laboratory animals such as rodents are capable of hearing. Most rodents can detect sounds from 1000 Hz (the frequency of the Greenwich Time Signal) up to 100000 Hz, depending on the strain, with usually one or more commonly two peaks of sensitivity within this range. Dogs can detect sound most easily from 500 Hz to 55000 Hz, depending on the breed.2. Rodents also produce sound signals as a behavioural response and for communication in a variety of situations. Ultrasonic calls in the range 22000–70000 Hz are the main communicating pathway during aggressive encounters, mating, and mothering. Similar calls have also been recorded from isolated animals associated with inactivity, rest and possibly even sleep.3. Very loud sounds cause seizures in rats and mice, or can make them more susceptible to other sounds later in life. This effect is possible even when animals are fully anaesthetized. Sound tends to startle and reduce activity in several species of animal. Even offspring of mice that have been sound‐stressed exhibit abnormal behaviour patterns. Sounds also elicit various responses in rats from increasing aggression to making them more tolerant to electric shocks.4. Levels of sound above 100 dB are teratogenic in several species of animals and several hormonal, haematological and reproductive parameters are disturbed by sounds above 80 dB. When rats are chemically deafened the disturbance to their fertility disappears. Lipid metabolism is disrupted in rats when exposed to over 95 dB of sounds, leading to increases in plasma triglycerides. Atherosclerosis can be produced in rabbits by similar levels of sound.5. It has also been shown in guinea pigs and cats that hearing damage is governed by the duration as well as the intensity of the sound and is irreversible. Work on chinchillas hs demonstrated that sounds above 95 dB lead to this injury, but that sounds of 80 dB have no permanent effect on hearing sensitiv

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1982.tb00703.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

SummaryI. Information on growth, development and care of young has been assembled for 62 species of marsupial.2. During gestation, development of the marsupial embryo proceeds only so far as to allow the neonate to make its way from the urogenital opening to the mammary area on the abdomen of the female where it attaches to a teat. Specific structural adaptations keep the neonate firmly attached to the teat for at least the first month after birth.3. Six types of pouch are distinguished ranging from lateral folds of skin, which do not cover the mammary area or enclose the developing young, to a fold of skin that covers the mammary area and forms a deep pouch, completely enclosing the developing young.4. Although the young is very small at birth and birth is rapid, specific changes in the behaviour of females occur around the time of birth, and a specific birth position is adopted.5. The time at which marsupial young leave the pouch cannot be equated with birth in eutherians, because of the considerable variations in the type of pouch and in patterns of parental care. From a consideration of the functional development of the young in the pouch, it is suggested that the nearest equivalent to eutherian birth is the time at which the marsupial young achieves homeostasis, when it is well furred and endothermic.6. Maternal behaviour is influenced by the type of pouch. In all species, the mother keeps the young and the pouch clean by licking, especially when the young are wholly within the pouch or attached to the abdomen. In species with reduced pouches where young are left in a nest at an early stage of development, maternal behaviour includes nest building, defence, and retrieving and carrying the young. These functions are performed by the pouch itself in species with large deep pouches in which the young is carried for a much larger part of its development, and other specific maternal behaviours are infrequent.7. The patterns of parental care are reviewed over all families of marsupial. Not all members of a family have the same pattern of parental care, which appears to be influenced by many factors including body size, type of pouch, diet, litter size and other aspects of life history strategy.8. Three patterns of parental care are distinguished:(A) As soon as young begin to release the teat they are no longer carried by the mother, and are left in a nest when still barely furred, ectothermic and before the eyes open. This pattern is found in species with large litter size and a pouch reduced or absent, e.g. some Dasyuridae and some Didelphidae.(B) Young remain in the pouch after they begin to release the teat but are left in a nest, at a later stage of development than in A, when well furred, endothermic and with eyes open. After first pouch exit, there is generally a period when young return to the pouch from time to time. This pattern is found in species with well developed pouches and litters of I or>1 e.g. Peramelidae, some Didelphidae.(C) Young remain in the pouch after they begin to release the teat. At first pouch exit, the young is well furred and endothermic, and leaves the pouch only for brief periods, gradually spending more time out until permanent pouch exit. It is not usually left in a nest. This pattern is found in species with well developed pouches and litters of one, e.g. Macropodidae.9. Pattern A is seen particularly in the smaller species in any family, where large litter size means that by the time young release the teat, the litter is about 50% of maternal body weight and a considerable burden. In such species, young are left in a nest as soon as possible. In larger species with patterns B or C, litter size is smaller, and by the time they are no longer carried by the female, the litter is still only 20% of maternal weight.10. Whatever the pattern of parental care, mortality from birth to permanent pouch exit is not unusually high in marsupials in comparison with eutherians.11. I suggest that the presence of the pouch and the associated patterns of parental care are important determinants of social organization in marsupials. For much of the period of dependence, the young is small, attached to a teat or in a pouch. The male can make little contribution to parental care, and there is little room for improvement in the care of young in complex social groups. In most species, the female on her own is sufficient caretaker. The male is most likely to increase his own biological fitness by going off to mate again and leaving the female to raise his offspring.12. Patterns of energy expenditure on offspring by female marsupials were assessed throughout the development of young. Investment before birth was assessed by weight of the neonate, during development by growth rate and the time for which the young was carried (pouch life), and total investment by weight of young at weaning and time from birth to weaning. Regression of measures of investment against maternal body weight allowed comparison of investment in animals of different size.13. Investment in young before birth is very small. Neonatal marsupials range in size from 0·01 to 1 g, and the largest is less than 0·2 % of the size of the mother. Larger mothers produce larger young which are smaller relative to the mother than are the young of smaller species. Individual young in the family Dasyuridae are particularly small.14. Growth rates in g/d were calculated over the period from permanent pouch exit to weaning. There is a very close correlation between growth rate and maternal body weight ‐ that of litters increases as the 0·78 power of body weight. During this period the growth rate of individuals is comparable with that of eutherian young during lactation, and in litters it is higher still, suggesting that the difference in patterns of growth are not due to the lower metabolic rate of marsupials. As in eutherians there is considerable individual variation in growth rate; it is very high in litters of small dasyurids, which have individual rates comparable to those of larger species. Young of the family Peramelidae grow and develop rapidly; those of the arboreal folivorePhascolarctosdo both slowly.I 5. Pouch life, the period for which the young is carried by the mother, increases with body size; as expected, species with pattern A parental care have shorter pouch lives than species of the same size with patterns B or C, reflecting the early stage of development at which young are left in the nest in pattern A.16. Time from birth to weaning is also longer in larger species. There is a close relationship of age at weaning with maternal weight, with some significant exceptions. For their size, the family Peramelidae have a very short time from birth to weaning, and the time from pouch exit to weaning is particularly short. Many arboreal species have longer periods of dependence than expected from their size.17. The weight at weaning of individual young is closely related to MBW0·71, but the weight of one young relative to maternal body weight shows no trend with size, and ranges from 25–61 %, with a mean of 42 %.18. Parental Investment, as measured by the function Wt. of litter at weaning × 100/MBW, decreases with increasing size of mother as MBW0·28. The highest levels of investment are found in very small species. In many small species of the family Dasyuridae, a litter at weaning is>300% MBW. By contrast, investment in the family Peramelidae is low ‐ at weaning a litter of three is about 50% MBW, comparable with investment in a single young of the family Macropodidae.19. The evolution of patterns of parental care and investment appears to follow three main lines:(1) Species with large litter size, high levels of investment in litters and in individual young. Investment is directed to growth and not to carrying the young in the pouch, since young are left in a nest at an early stage. Typical of this group is the family Dasyuridae, in which many species make few reproductive attempts per year.(2) Species with litters of more than one, low levels of investment in litters and in individuals, but rapid growth and development of young. Because of the smallze of young they are carried in the pouch for a large part of the period from birth to weaning. This pattern is shown by the family Peramelidae, and seen as an adaptation to rapid and repeated reproduction in an environment with an extended favourable season.(3) Species with small litter size, lower total investment, but investment in individual young is not low, and investment in carrying young to an advanced stage of development is high. Patterns of this type are found in the Diprotodonta, with extreme development in the Macropodidae.20. Many of the measures of investment have been expressed as a power function of maternal body weight. The exponents of body weight in these functions are such as to suggest that an important underlying variable is metabolic rate.21. It has been suggested elsewhere that the marsupial mode of reproduction evolved as an adaptation to environmental uncertainty, in that it allows a reproductive attempt to be abandoned at any time much more readily than in eutherians, thereby increasing the likelihood that a female will survive to reproduce again. I consider this suggestion in the light of patterns of parental investment. For small, short‐lived species, any reproductive attempt represents a substantial part of its lifetime reproductive output. Investment in any one reproductive attempt is high, and the cost of replacing an abandoned attempt is so high that it seems unlikely that the desertion of offspring would be an important reproductive strategy in small ancestral marsupials, although it may be an important response to environmental uncertainty in certain large modern macropodid

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1982.tb00704.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

摘要:

SummaryI. Reliability of the results of bio‐medical research clearly depends upon the animals used showing as standard responses as is possible.2. The majority of animals used in this field are small, homoiothermic mammals which have sensitive and strong homeostatic mechanisms. If a change in ambient conditions is of sufficient magnitude to unbalance homeostasis, then the neuroendocrine system is stimulated so as to restore it, and this can interfere with the response to test conditions or agents.3. The homeostatic effectors involved are diverse and can include both physiological and behavioural changes in the animal. These can affect metabolic rate, body temperature, activity, food consumption, hormone concentration, wake/sleep patterns, maturation, posture, lactation and many other bodily functions. Any of these changes is potentially capable of influencing experimental results.4. The evidence presented shows how environmental factors may affect the outcome of experiments in the fields of animal behaviour, cancer research, immunology, pathology, pharmacology, psychology, reproduction, teratology and toxicology; particular attention is paid to the effects of ambient temperature, relative humidity, air movement and quality, light and sound.5. While a constant, reproducible environment would be ideal, there is little possibility of controlling all the variables; nevertheless all investigators should minimize those environmental variables that have been shown to be important.6. To enable other investigators to repeat experiments or carry out comparative studies, environmental conditions pertaining during an experiment should be adequately described in any publication

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1982.tb00705.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1982.tb00706.x

出版商:Blackwell Publishing Ltd    

年代:1982

数据来源: WILEY