摘要:

SummaryThe adaptation of the various mammals to all gradations between a totally diurnal to a totally nocturnal pattern of activity is noted and the nature of the determinants of the high proportion of species which are crepuscular or nocturnal is discussed. It is seen that detailed study of the activity patterns has been confined to a small proportion of species, principally some of the smaller rodents. Ruminants are unusual in remaining vigilant during normal sleep, loss of awareness of external events being confined to periods of paradoxical sleep which occupy a very small proportion of the 24 hours.The 24 hour rhythm of activity has an endogenous basis. Under normal conditions it is entrained by the changes in light intensity at dusk and dawn, but circadian activity rhythms can be entrained to periodicities longer or shorter than 24 hours. Relatively small variations in the intensity of the lighting between day and night are effective in maintaining entrainment, but under arctic conditions in summer the 24 hour rhythm becomes much less pronounced and activity may even develop a free–running pattern.A short–term rhythm with a regular periodicity of a small number of hours has been reported to occur by many authors in species of small eutherian mammals feeding on a bulky diet, that is insectivores and the more herbivorous of the small rodents. A summary account is given of information, much of it derived from unpublished research, indicating that in fact the patterns of diel activity of such rodents vary greatly with the environmental conditions. The duration of daylight is apparently only one of many factors affecting the distribution of their activity over the 24 hours. It is noted that versatility of this nature also occurs in some large mammals.It is concluded that an advance in knowledge of the mechanisms determining the activity patterns of mammals will require a greater emphasis on field observations of mammal behaviour and on laboratory experiments in which the variety of conditions found in nature is closely simula

ISSN:0305-1838    

DOI:10.1111/j.1365-2907.1972.tb00088.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

SummaryMammals show numerous circadian rhythms, some exogenous but nonetheless useful, some endogenous. Even in the absence of exogenous synchronizers, different physiological functions usually preserve their normal temporal relations, suggesting that a single clock controls most or all of the rhythmic manifestations. The role of adrenal corticosteroids and of temperature as means whereby the clock influences other functions is considered.

ISSN:0305-1838    

DOI:10.1111/j.1365-2907.1972.tb00089.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

ISSN:0305-1838    

DOI:10.1111/j.1365-2907.1972.tb00090.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

SummaryMoulting in mammals is a cyclic phenomenon which often occurs in a wave–like pattern. The moult cycle depends upon an inherent rhythm of activity in the hair follicles, which may be modified by systemic factors. In laboratory rodents a number of hormones affect the timing of the moult, as well as affecting the amount of hair produced and the loss of club hairs.InMicrotus agrestisa seasonal moult results in a sparse coat with coarse hairs in summer and a dense coat with fine hairs in winter. The moult appears to be adjusted to the environment by way of the endocrine system, with adrenal and thyroid hormones, as well as sex hormones, involved in the regulation. The importance of such adaptive coat changes are discusse

ISSN:0305-1838    

DOI:10.1111/j.1365-2907.1972.tb00091.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

SummaryThe differing types of oestrous cycle found in mammals seem to be manifestations of the degree to which the external environment participates in the control of the three main phases of the ovarian cycle, the follicular phase, ovulation, corpus luteum phase. The question of the importance of the external and the internal environment for the manifestations of cyclicity has been discussed by reference to the factors involved in the control of ovarian function. The control of the ovarian cycle involves an interrelated fluctuation in the secretion of the anterior pituitary gonadotrophins FSH and LH, and in certain species LTH, which are under the control of hypophysiotrophic hormones produced in the hypothalamus. The production of these hormones is modified by other hypothalamic and extra–hypothalamic mechanisms, including a probable preoptic cycling mechanism controlling the ovulatory surge of gonadotrophins. These mechanisms can be triggered and timed by means of nervous reflexes arising from a variety of sensory end organs. Also this brain–hypothalamus–pituitary unit appears to contain sex steroid and gonadotropin sensitive elements through which these factors can influence the system. The additional luteotrophin and luteolytic factors involved in corpus luteum control have not been discussed. A brief idea as to how all these factors are integrated for the control of ovarian cyclicity is pres

ISSN:0305-1838    

DOI:10.1111/j.1365-2907.1972.tb00092.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

SummaryStudy of the causation of seasonal breeding can be subdivided into a consideration of external or ecological, and internal or physiological, factors. Of the ecological ones, the role of day–length has been most extensively studied. Subjecting appropriate animals to different photoperiods should give fresh insight into mechanisms of the central nervous system. Alterations in day–length may produce changes in the C.N.S. and pituitary quite quickly, say within 24 to 48 hours. But there is still uncertainty about such basic problems as the relative significance of abrupt and gradual changes in day–length for the alteration of gonadal activity; and the existence of an annual endogenous physiological rhythm which may provoke the gonads into activity at the appropriate time. In addition, for some small rodents physical environmental factors apparently are not always equally efficient in stopping breeding in the winter, and it may be that length of breeding season is also influenced by biotic factors, such as the phase of a population cycle. Susceptibility to the effects of short photoperiods (“winter”) may be to some extent genetically controlled. Possibly then genotypes allowing winter breeding may be favoured at some, but not other, phases of populati

ISSN:0305-1838    

DOI:10.1111/j.1365-2907.1972.tb00093.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

摘要:

SummaryThe seasonal or cyclical changes in the size, histology and secretions of the male reproductive organs and accessory glands of certain mammals are reviewed briefly. Some mammals such as man and the laboratory rat are fertile throughout the year whereas others such as the Red deer stag and the mole are fertile only at certain periods. The male's cycle cannot necessarily be inferred from the female's cycle in those mammals that have a seasonal cycle, neither can it be inferred from rutting or copulatory behaviour. In some species the male is fecund throughout the year whereas the female has a well defined breeding season or seasons, which is defined as the period between conception and parturition. It is stressed that morphological changes, whether macroscopic or histological, do not necessarily reflect the secretory activity of the gland and that the presence of spermatozoa indicates fecundity, not fertility.The information available on the reproductive organs, accessory glands and breeding cycles of mammals which occur in Britain is summarized. The majority of these mammals exhibit a seasonal cycle. The reproductive cycle of Fallow, Red and Sika deer, which are temperate species, can be correlated with the shedding and growth of antlers; for Red and Sika deer this is controlled by changes in the photoperiod. Two tropical mammals, the wildebeest and the hippopotamus, are considered and in the wildebeest we may have an animal which has a well–defined rutting period although spermatogenesis proceeds throughout the year. Although the male hippopotamus is sexually active throughout the year, there are peaks in the calving season which can be correlated with the rainy seasons. In some hibernating insectivores and rodents, recrudescence of the gonads and accessory glands begins before hibernation finishes. In temperate bats insemination usually takes place in the Autumn and this is followed by hibernation, fertilization not taking place until the Spring. Fertilization in some species ofMiniopterustakes place after copulation but growth of the embryo is retarded during hibernation.Finally, the causes of the cyclical waxing and waning of the reproductive organs and accessory glands and the effects of various external stimuli are considered. Very little experimental work has been done in this field apart from that on the effect of light on some domesticated specie

ISSN:0305-1838    

DOI:10.1111/j.1365-2907.1972.tb00094.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY

ISSN:0305-1838    

DOI:10.1111/j.1365-2907.1972.tb00095.x

出版商:Blackwell Publishing Ltd    

年代:1972

数据来源: WILEY