ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1989.tb00677.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SummarySince trehalose in insects, in contrast to glucose in mammals, does not enter the haemolymph directly from the digestive tract, but is all synthesized by the insect itself, and furthermore an increased trehalose synthesis during stress and flight does not lead to significant increases in haemolymph trehalose, there seems to be no physiological need for an insect homeostatic hypotrehalosaemic hormone. Experiments in which tissue extractions were found to lower haemolymph trehalose cannotprove the existence of such a hormone, while all insect species which so far have been submitted to a trehalose‐tolerance test, decrease their haemolymph trehalose concentrations at a rate which can be accounted for by the metabolic use of trehalose. These results therefore indicate the absence, and not the presence, of a homeostatic hypotrehalosaemic hormone. This is also true for blowflies, from which an insulin‐like immunoreactive peptide has been isolated. It seems therefore unlikely that this insulin‐like peptide is a homeostatic hypotrehalosaemic hormone. The physiological mechanism by which this insulin‐like peptide would have to act to function as a hypotrehalosaemic hormone is also an unlikely one. It therefore seems justified to conclude that so far, homeostatic hypotrehalosaemic hormones have not been demonstrated in insects. Furthermore, it may well be that they do no

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1989.tb00678.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SummaryThe house mouse,Mus domesticus, can thrive in natural environments much below its optimum temperature. Thermogenesis is then above that at more usual temperatures. In addition, body weight, and the weights of brown adipose tissue and the kidneys, may be higher than usual. In free populations of house mice cold lowers fertility and may prevent breeding. Other possible limiting factors on breeding are food supply, shelter for nesting and social interactions.In captivity, wild‐type house mice exposed to severe cold (around o °C) at first adapt ontogenetically by shivering and reduced activity. But raised thermogenesis is soon achieved without shivering; nest‐building improves; and readiness to explore may be enhanced. Endocrine changes probably include, at least initially, a rise in adrenal cortical activity and in catecholamine secretion. Some females become barren, but many remain fertile. The maturity of fertile females is, however, delayed and intervals between births are lengthened; nestling mortality rises. A limiting factor during lactation may be the capacity of the gut. Similar adaptive changes are observed during winter in some species of small mammals that do not hibernate. But neither the house mouse nor other species present a single, universal pattern of cold‐adaptation.Wild‐type mice bred for about 10 generations in a warm laboratory environment (20–23 °C) change little over generations. In cold they become progressively heavier and fatter at all ages; they mature earlier, and nestling mortality declines. The milk of such ‘Eskimo’ females is more concentrated than that of controls. If ‘Eskimo’ mice are returned to a warm environment, they are more fertile, and rear heavier young, than controls that remained in the warm. Despite the heavier young, litter size is not reduced: it may be increased, probably as a result of a higher ovulation rate.Parental effects have been analyzed by cross‐fostering and hybridizing. Survival, growth and fertility are all favourably influenced by the intra‐uterine and nest environments provided by ‘Eskimo’ females. ‘Eskimo’ males are also better fathers. Hence after ten generations the phenotype of cold‐adapted house mice shows the combined effects of (a) an ontogenetic response to cold, (b) a superior parental environment and (c) a changed genotype.The secular changes in the cold that lead to this phenotype give the appearance of evolution in miniature; but it is equally possible that they represent a genetical versatility that allows rapid, reversible shifts in response to environmental demands. The adaptation of house mice to extreme environments, whether progressive or reversible, is aided by a comple

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1989.tb00679.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

SummaryA search of plant breeding literature has produced 69 examples in which reasonable judgements could be made as to potential for genetic advance. The crops covered are all inbreeders (predominantly cereals) or outbred clones. The average potential for genetic advance (roughly 60 % of examples were favourable) seemed to be far higher than would usually be expected and to indicate therefore that excellent new crop varieties should be more frequent than experience suggests. The discrepancy may be partly explained by various biases but the main conclusion is that superior genotypes are indeed fairly frequent but that selection efficiency is too low to take better advantage of them.

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1989.tb00680.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Summary1. The climate changes drastically above the timberline. Diverse adaptations have been evolved by insects and other terrestrial arthropods to survive the alpine environment. The fitness of each species depends on a combination of different factors in accordance with their special habitats.2. Morphological adaptations such as reduced body‐size, are known from a number of alpine insects, increasing their possibility to find sheltered microhabitats. Selection for reduced body size in AndeanPhuliaspp. butterflies is probably a result of their rigorous environment. Wing atrophy, which is also known in insects from other extreme environments, is widespread in alpine species. In several terrestrial arthropods the absorption of solar radiation is increased by melanism. Increased pubescence, protecting against the loss of heat, is known in alpine butterflies and bumblebees.3. Several behavioural adaptations are described. Thermoregulatory behaviour is important in many species to raise their body temperatures. Alpine butterflies orient the dark basis of their wings perpendicular to the rays of the sun. Body temperatures of 30 °C may be required for flight. To increase their activities many alpine terrestrial arthropods seek warmer microhabitats in the vegetation and under rocks. The adaptive advantage of nocturnal activity as observed in several species, may be to maintain the water balance or to avoid predation.4. Tropical alpine terrestrial arthropods are faced with special problems. The large diel temperature fluctuations require cold‐hardiness during the night and tolerance to heat during the day. Many species seek sheltered microhabitats under rocks and in vegetation.5. Due to low precipitation and high evaporation rates many mountain areas are extremely dry. High resistance to desiccation may be very important to alpine species, and in particular to tropical species. Rates of water loss at low relative humidities are comparable to those of desert arthropods.6. As an adaptation to the cold alpine summers several species of terrestrial arthropods require more than one year to complete their life‐cycles. Special to these species is their adaptation to low temperatures in two or more overwintering stages. In spite of their cold surroundings several species have univoltine life cycles, frequently combined with highly specialized adaptations. Increased metabolic rates as a compensation to low temperatures may be widespread in alpine species, but few data are available.7. Cold tolerance is of particular importance in temperature alpine species. Winter survival in Collembola and Acari depends on supercooling. Great seasonal variations have been observed in a number of species. Freezing tolerance is also known from alpine insects, e.g. in some species of beetles. At high latitudes alpine species must endure periods of up to eight or nine month at low temperatures during hibernation. Anaerobiosis is known from species that are enclosed in ice, with lactate as the main end product of meta

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1989.tb00681.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Summary1. Non‐pathogenic microorganisms, known as mycetocyte symbionts, are located in specialized ‘mycetocyte’ cells of many insects that feed on nutritionally unbalanced or poor diets. The insects include cockroaches, Cimicidae and Lygaeidae (Heteroptera), the Homoptera, Anoplura, the Diptera Pupiparia, some formicine ants and many beetles.2. Most mycetocyte symbionts are prokaryotes and a great diversity of forms has been described. None has been culturedin vitroand their taxonomic position is obscure. Yeasts have been reported in Cerambycidae and Anobiidae (Coleoptera) and a few planthoppers. They are culturable and those in anobiids have been assigned to the genusTorulopsis.3. The mycetocyte cells may be associated with the gut, lie free in the abdominal haemocoel or be embedded in the fat body of the insect. The mycetocytes are large polyploid cells which rarely divide and the symbionts are restricted to their cytoplasm.4. The mycetocyte symbionts are transmitted maternally from one insect generation to the next. In many beetles (Anobiidae, Cerambycidae, Chrysomelidae and cleonine Curculionidae), the microoganisms are smeared onto the eggs and consumed by the hatching larvae. In other insects, they are transferred from mycetocytes to oocytes in the ovary, a process known as transovarial transmission. The details of transmission in the different insect groups vary with the age of the mother (adult, larva or embryo) at which symbiont transfer to the ovary is initiated; whether isolated symbionts or intact mycetocytes are transferred; and the site of entry of symbionts to the egg (anterior, posterior or apolar).5. Within an individual insect, the biomass of symbionts varies in a regular fashion with age, weight and sex of the insect. Suppression of symbiont growth rate and lysis of ‘excess’ microorganisms may contribute to the regulation of symbiont biomass.6. Aposymbiotic (symbiont‐free) insects and isolated symbionts (including freshly‐isolated preparations of unculturable forms) are used to investigate interactions between the partners. However, some methods to obtain aposymbiotic insects (e.g. antibiotics and lysozyme) deleteriously affect certain insects and aposymbionts may differ from the symbiont‐containing stocks from which they were derived.7. The mycetocyte symbionts have been proposed to synthesize various nutrients required by the insect. The symbionts of beetles and haematophagous insects may provide B vitamins and those in cockroaches and the Homoptera essential amino acids. The role of symbionts in the sterol nutrition of insects is equivocal.8. Mycetocyte symbionts may have evolved from gut symbionts or guest microorganisms. The association is monophyletic in cockroaches but polyphyletic in many groups, including the sucking lice, beetles and scale insects.9. The mycetocyte symbioses are commonly regarded as mutually beneficial but the selective advantage to the microbial partner is unclear. It is proposed that these associations should be described exclusively in terms of the advantage to the insect which, by gaining symbionts, acquires novel metabolic capabilities, e.g. essential amino‐acid and

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1989.tb00682.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

Summary1. Freshwater fishes are the most northerly of freshwater ectotherms, followed by frogs. North American freshwater snakes, turtles, and salamanders do not range farther north than southernmost Canada.2. Freezing and desiccation are the main challenges during terrestrial hibernation of ectotherms. Oxygen depletion, water balance, and ionic balance are the major problems for air breathing ectotherms that hibernate underwater.3. The importance of accumulation of energy stores for overwintering among fishes depends upon the length and severity of the winters, whether or not there is springtime reproduction, body size, latitude, and the availability and use of food during overwintering.4. Fishes can decrease energy demands during the winter by reductions in activity, metabolic depression, and entrance in semi‐torpidity.5. Adaptations for coping with hypoxia and anoxia among overwintering freshwater fishes may include metabolic depression, a decrease in blood O2affinity, microhabitat selection, air breathing, short‐distance migration, biochemical modifications aimed at adjusting glycolytic rates, and alcoholic fermentation.6. Freshwater turtles have a worldwide northern limit of approximately 50° N, which means that some species spend about half of their lives hibernating.7. Aquatic turtles normally hibernate underwater, although occasionally they hibernate on land. In water they usually hibernate in a hypoxic or anoxic (mud) environment and in relatively shallow water. Wintertime movements of unknown frequency occur in some species.8. The hatchlings of many turtle species can overwinter in the nest. Among northern species this behaviour is most common among painted turtles, whose hatchlings can withstand freezing.9. Mortality among adult turtles is probably highest during the hibernation cycle.10. Temperature appears to the most important cue for entry and exit from hibernation among freshwater turtles.11. Little is known of the energetics of overwintering turtles. Energy stores for overwintering may be more important at lower latitudes than at higher ones, due to the higher metabolic rates of overwintering, but non‐feeding, southern turtles.12. The ability of turtles to tolerate submergence is a function of temperature, degree of water oxygenation, latitude of origin, efficacy of extrapulmonary respiratory pathways, and metabolic rate.13. For turtles that hibernate in an anoxic hibernaculum, and for those without sufficient extrapulmonary uptake of O2to allow metabolism to be completely aerobic, the most important physiological perturbation is an acidosis developed from a continuing production of lactate. If sufficient O2can be obtained, the most likely factors limiting hibernation time are water balance and ion balance.14. Mechanisms of turtles for coping with acidosis include metabolic depression, integumental CO2loss, bicarbonate buffering, and changes in ion concentrations that minimize the decrease in SID (strong ion difference). The most important among the latter are a decrease in plasma [Cl‐] and large increases in plasma calcium and magnesium.15. Turtles are unique among reptiles in their ability to maintain both cardiovascular and nervous system function during prolonged anoxia.16. Turtles gain weight from water uptake during submerged hibernation, but apparently maintain some kidney function; however, osmoregulation is one of the least known areas of the physiology of hibernation.17. Recovery of turtles upon emergence commences with a rapid hyperventilatory compensation of pH, followed by a slower adjustment of ion levels. Basking speeds recovery greatly.18. While hibernation of turtles in the northern parts of their ranges is most likely very stressful physiologically, northern range limits are more likely to be determined by reproductive restraints than by the rigors of extended hibernation.19. The superior ability of turtles to tolerate anoxia may be more the result of an annual hibernation than of their diving habits during active periods of the year.20. Freshwater snakes usually hibernate on land. However, they appear to be capable of aquatic hibernation and may not do so because of the risk of death from anoxia.21. Some species of terrestrial snakes are known to hibernate underwater, and are able to do so in the laboratory for months. In the field, this behaviour is considered opportunistic, as there is no evidence to suggest that any snakes can tolerate extende

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1989.tb00683.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1989.tb00684.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1989.tb00685.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY