摘要:

ABSTRACTLactation is central to mammalian reproduction, and an understanding of the origins of lactation is necessary to comprehend the early evolution of the Class Mammalia. In modern mammals, lactation is a staggeringly complex phenomenon involving morphological, physiological, biochemical, ecological, and behavioural adaptations. Because such a complex web of adaptations could not have arisende novo, lactation must have begun as a much simpler process. Hypotheses regarding the original adaptive value of proto‐lacteal secretions invoke thermoregulatory, antibiotic, behavioural or nutritive functions. In this review, we evaluate each of these hypotheses and attempt to reconstruct the origins of lactation in the light of current concepts of the biology of early mammals and their ancestors, the origin of mammary glands, the evolution of extravitelline nutrient provision, and the physiology and biochemistry of milk synthesis and secretion. Drawing upon empirical evidence and theoretical considerations, we present a gradualistic scenario involving the following steps. First, incubation of eggs was aided by development of a vascularized abdominal incubation patch. Secondly, anti‐microbial secretions from cutaneous glands of the incubation patch enhanced survival of eggs or offspring. At this stage, these secretions could have supplemented vitelline nutrients (in much the same way as oviductal secretions do in monotremes), perhaps facultatively. Subsequently, hypertrophy and specialization of cutaneous glands accompanied the controlled production of a copious, nutritious secretion, which eventually evolved into a primary source of energy for development and growth of the offspring. We outline important events in the evolution of milk, and suggest studies likely to provide indirect tests of the evolutionary hypotheses discus

ISSN:0305-1838    

DOI:10.1111/j.1365-2907.1989.tb00398.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

ABSTRACTIn the last 8 years, examples of prolonged sperm storage, delayed implantation and retarded embryonic development have been reported from some South temperate Old World Microchiroptera. It is suggested that in the species concerned, hibernation or prolonged periods of hypothermia restrict all reproductive processes to the summer months (September to April) and that this 8‐month period is too short to accommodate a ‘typical’ microchiropteran reproductive cycle. Consequently some form of reproductive adaptation, in which a period of delay occurs in the reproductive cycle, is one requirement for hibernating bats in subtropical and temperate latitudes. The inclusion of a period of reproductive delay during winter effectively lengthens the reproductive cycle and allows gametogenesis to be initiated in the middle of one summer, and parturition to occur early the following summer. It is suggested that the type of reproductive delay evolved by a species may be related to its pattern of winter activity.SUMMARYIt is suggested that in the hibernating members of the Vespertilionidae and Rhinolophidae the typical tropical reproductive strategy of seasonal monoestry has been modified by the inclusion of a period of reproductive delay. The principal effect of this is to lengthen die reproductive cycle so that gametogenesis is initiated in the middle of one summer, and parturition and lactation occur during the following summer, when food is abundant. The diree reproductive delay phenomena recorded in Microchiroptera from Soudi Africa should be regarded as different ways of lengthening the reproductive cycle, possibly determined by the winter activity of the species. Although these ideas are based on observations of the reproduction of African bats, they can equally be used to explain die evolution of reproductive delays in north temperate

ISSN:0305-1838    

DOI:10.1111/j.1365-2907.1989.tb00399.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY

摘要:

ABSTRACTWe made a preliminary survey of the present status and ecology of the White‐lipped Deer(Cervus albirostris)in the upper Huang He and Chang Jiang River regions of China. Eight mixed herds, ranging in size from 5 to 46 animals each, were observed. The deer lived from the rhododendron scrub just above the spruce forests to alpine grasslands, ranging in altitudes from 4000 to 5000 m. The peak of the rut occurred in October, when breeding herds were composed of a few large stags and hinds. The pasturing of domestic animals in the area influences not only the spatial distribution of the deer, but also the timing of seasonal shifts. The main distribution of the deer is in western Sichuan Province and some scattered populations in Qinghai Province are endangered. The species could survive, given adequate protectio

ISSN:0305-1838    

DOI:10.1111/j.1365-2907.1989.tb00400.x

出版商:Blackwell Publishing Ltd    

年代:1989

数据来源: WILEY