摘要:

Summary1. Life expectancy and mortality rates from diseases arising in various organs vary with sex because of differential exposure to external hazards and because of essential differences between males and females in aspects not directly connected with reproduction. This review attempts to collate data about the structural and functional dimorphism of mammals exclusive of the genital organs and psychological aspects.2. The primary sex ratio is not certain and like the secondary and tertiary may vary with species. In many mammals more males are aborted and born than females. Later a higher mortality of males, due to sex‐linked congenital diseases and greater exposure to external hazards, shifts the balance in favour of females at the time of sexual maturity. The average life span of females is longer than that of males, except in hamsters and in inbred strains of mice with a high incidence of mammary tumours.3. Chromosomes as well as gonadal hormones are responsible for the development of male and female characteristics. The Y‐chromosome initiates the differentiation of the testis, but gonadal hormones control the subsequent differentiation of the genital tract and other organs. In embryos the testicular secretion precedes that of the ovary. The Y‐chromosome is devoid of, but the X‐chromosome retains structural genes. The random heterochromatization of a paternal or a maternalX‐chromosome in the somatic cells of female embryos equalizes the genetic information for both sexes and produces a mosaicism of female somatic cells except in the kangaroo where the paternal X‐chromosome is selectively inactivated. Deficient genes on theX‐chromosome become manifest in hemizygous males, in homozygous females and can be detected in heterozygous women in half of the somatic cell population in some conditions.4. The testis grows faster than the ovary and starts to secrete earlier, but the maturation of female gonocytes precedes that of males. Spermatogenesis starts at puberty and is maintained throughout life, while multiplication of oogonia ceases in the perinatal period (except in lemurs), when the stage of the first meiotic division is reached. The stock of oocytes dwindles during life.5. In many mammals the male grows faster than the female before and after birth, but is less mature. Puberty tends to start earlier in females and the associated growth spurt does not last as long as in males. Testosterone has a direct anabolic effect, promotes growth and delays differentiation. Oestrogens are considered katabolic, but promote growth indirectly by stimulating the production of growth hormone in the pituitary. Progesterone has an anabolic and slight androgenic effect.6. A female pattern of differentiation of the hypothalamus, the pituitary and the pineal gland, manifested at puberty by cyclical activities of the reproductive organs requires the absence of androgens during a critical phase of ante‐ or perinatal development. Oestrogens given to males at that period produce effects similar to castration. Antiandrogens induce in males a cyclical pattern of function in the hypothalamus and the pituitary, enlargement of the breasts and formation of nipples in the rat and a female type of sexual behaviour. There is no complete sex reversal in mammals comparable to that of fish and amphibians.7. With some exceptions (hamsters, rabbits, guinea‐pigs) males are larger than females. Gender differences in weight of organs and in other parameters must be assessed as proportion to male or female weight, surface and activities. The relatively greater amount of fat in female and of connective tissue in male organs in relation to the active parenchyma complicate comparisons.8. The head and shoulder region is proportionately larger in males and the pelvic region in females. Men and male mice have heavier bones, muscles, hearts, lungs, salivary glands, kidneys and gonads in proportion to body weight, while females have proportionately heavier brains, livers, spleens, adrenals, thymus, stomach and fat deposits.9. The basal metabolic rate in women is lower than in males. A great variety of metabolic parameters, levels of enzyme activity, location of fat deposits, sensitivity to drugs is sexually dimorphic and responsive to the action of androgens, oestrogens and progestagens.10. Males tend to have more red blood corpuscles, haemoglobin and erythropoietin per unit volume of blood than women, cows, mares, sows, bitches, female cats and hamsters, but there is no sex difference in this respect in rats, rabbits, goats or sheep. Females tend to have more granulocytes and a proportionately larger lymphomyeloid complex (bone marrow, spleen, thymus, lymph nodes and lymphoepithelial tissues) and greater immunological competence than males. The cortical epithelium of the thymus in mice and rats is sexually dimorphic, responsive to castration and treatment with sex hormones and varies with the oestrous cycle.11. The kidney is proportionately larger in male mice, rats, cats and dogs, is reduced by castration and enlarged by treatment with testosterone. The kidneys of hamsters and guinea‐pigs do not differ in size with sex, nor do they respond to castration or to androgens. The proportion of tubules to glomeruli is greater in the male than the female kidney. The tubular mass increases with androgenic medication, but not the juxtaglomerular apparatus. The parietal epithelium of Bowman's capsule, the histochemistry of the kidney and the composition of the urine vary with gender and respond to sex hormones according to species and strain. The bladder of male mice is proportionately larger than that of females. Some pheromones are present in the bladder urine of intact male mice and of spayed females given testosterone, but absent from that of castrated males.12. Boars, male elephants, mastodons, horses, deer and monkeys have larger canines than the females. The submaxillary gland of male mice, rats and pigs is proportionately larger than in females, but smaller in hamsters. The proportion of mucous to serous acinar cells in female rodents is greater than in males; female hamsters produce more sialic acid. The secretory tubules of male rats and mice are larger than in females and produce a nerve‐ and an epidermal‐growth factor. Apart from amylase the levels of enzyme activity vary with sex.The liver is sexually dimorphic as regards size, content and metabolism of glycogen, fat, vitamin A, levels of enzymatic activity, phagocytic activity and in its response to castration, sex hormones, to toxic agents, drugs and carcinogens. Sex hormones affect the production of insulin by the pancreasin vivoandin vitro.13. The male larynx which enlarges and induces voice changes in many mammals at puberty or the onset of the breeding season, is affected by castration and by sex hormones. Male lungs are proportionately larger than female ones with a greater vital and maximal respiratory capacity. Breathing rate and manner varies with sex and is related to differences in the muscular development of the diaphragm.14. The epidermis and dermis of males are thicker, but the subcutis thinner than in females. The skin is sexually dimorphic in respect of dermatoglyphics, the replacement of vellus by terminal hair and pigmentation of specific regions, the colour of the face and of the sexual skin in monkeys, the development of antlers and horns. The synchrony of the hair cycle and the growth wave of the hair coat in mice and rats depend on the sex of the animals. The X‐chromosome mosaicism in the hair follicles of female mice accounts for the mosaicism in pigmentation. Apart from a genetic disorder, the sweat glands are not sexually dimorphic, but the apocrine, the sebaceous glands and their specialized forms are. The embryonic development of mammary glands depends on the absence of androgens and can be induced in male rats and guinea‐pigs by antiandrogens.15. An intact cerebral cortex is necessary for the performance of reproductive functions in male, but not in female rats, cats, rabbits and guinea‐pigs. Removal of the olfactory bulb impairs reproduction in female, but not in male mitesticular atrophy of hamsters kept in the dark. The reproductive cycles in females are regulated by the hypothalamus through the control of the ratio of FSH to LH release in the pituitary. This in turn acts on the ovary and thus affects the activity of the thyroid, thymus and lung. In males FSH and LH act synergistically and their secretion is not controlled separately. Oestrogens are more effective than androgens in inhibiting pituitary functions.Sexual dimorphism in cytology, enzyme levels and oestrogen‐binding is manifest in the preoptic area, the hypothalamus and the nucleus medialis amygdalae. The female brain is proportionately larger than the male with equal relative amounts of grey and white matter, but a bigger hypothalamic‐pituitary‐pineal complex. The pineal gland is more prone to tumour formation in boys than in girls and retains its cellularity longer in women than in men. Colour blindness is manifested less in heterozygous women than in hemizygous men. Mature women are more sensitive to the smell of synthetic musk than girls or men. Male rats and mice are more susceptible to audiogenic seizures than females.16. The activity of the thyroid gland varies at different phases of the oestrous cycle in rats, mice and guinea‐pigs. Female mice release more thyroid hormone into the blood than males or spayed animals. Oestrogens increase the level of thyroxin‐binding protein. The concentration of TSH in the blood of mature women is double that of men and of menopausal women. The incidence of non‐endemic thyroid disorders in women considerably exceeds that in men.17. The adrenals of females are much larger than those of males except in hamsters. The gland of the female mouse contains more lipid than that of the male. The juxtamedullaryX‐zone of mice involutes at puberty in males and during the first pregnancy in females. Castration induces anX‐zone in male mice, voles, hamsters and cats and an enlargement without stratification in rats. ACTH controls the secretion of glucocorticoids and since its formation is promoted by oestrogens and inhibited by androgens, sex hormones influence indirectly the size and activity of the adrenal cortex. Hepatic inactivation of glucocorticoids is 3 to 10 times greater in intact females than in males.18. The implications of species variations in sexual dimorphism for the survival and the evolution of mammal

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1974.tb01171.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

Summary1. The conduction velocity of the compound action potential of peripheral nerves shows compensatory acclimation to temperature in a fish, a snail, a crab, and probably also in the frog. The heat and cold tolerances of peripheral conduction are probably both increased by cold acclimation in the frog.2. The properties of compound action potentials are not suitable for temperature acclimation studies, since different neuronal populations in the same nerve have been found to exhibit different temperature characteristics.3. Single but septate giant nerve fibres of earthworms show compensatory temperature acclimation of the conduction properties, the form of the action potential and of the axonal cable properties, especially below 13–19 °C.4. The fatty acids and the plasmalogen aldehydes of the phospholipids of the goldfish brain are more unsaturated at lower acclimation temperatures.5. The Na+‐K+ATPase activity of the earthworm nerve cord shows compensatory acclimation at low temperatures.6. The spontaneous activity of the central nervous system of insects is altered in a compensatory manner by temperature acclimation. In fish, the cold tolerance of simple and complex reflexes and of conditioning is adaptively altered by temperature acclimation. The role of the central nervous system, especially of the thermoregulatory centre, in the temperature acclimation of homeotherms is established.7. There are adaptive isoenzymes of acetylcholinesterase in the brain of the rainbow trout. These isoenzymes differ from each other in respect of the temperature dependence of their enzyme‐substrate affinity. The synthesis of acetylcholine receptor molecules may also be affected by temperature acclimation.8. The metabolism of putative synaptic neurotransmitters (5‐hydroxytryptamine, adrenaline, noradrenaline) is altered in the frog and mouse brains during the early phases of temperature acclimation. These changes may initiate the physiological processes connected with temperature acclimation.9. The neuromuscular transmission in the frog shows after acclimation to cold, increased resistance to it and some indications of temperature compensation.10. Changes in neurosecretion seem to be involved in temperature acclimation both in poikilotherms and homeotherms. The fast axonal transport of proteins shows compensatory acclimation to cold in

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1974.tb01172.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY

摘要:

Summary(1) The fluid properties of air and water enable animals to orientate to flow and this behaviour in water is termedrheotaxis. Fish, however, have a wide range of responses to currents, extending beyond simple orientation, and the termrheotropismis therefore used as a ‘portmanteau’ word to describe all such reactions.(2) Fish detect currents directly by flow over the body surface or indirectly by other stimuli. Indirect responses are more common and occur in response to visual, tactile and inertial stimuli resulting from displacement of the fish by the current. Reactions to displacement of visual images are calledoptomotor reactions. The lateral line is not involved except in the detection of small localized jets of water. It has not been demonstrated that any fish can detect the current by electrical stimuli, although it is theoretically possible for some to do so.(3) In the basic form ofrhotaxisthe fish heads upstream and maintains station by stemming the current. Current detection thresholds fall within the range 0.4 to 10 cm/s for tactile stimuli but may be as low as 0.03 cm/s for visual stimuli.(4) Visual responses have been studied by simulating displacement by the current in optomotor apparatus. Fish respond to a rotating black‐and‐white‐striped background by compensatory movements of the head and eyes ‐optokinetic nystagmus ‐or by theoptomotor reaction, in which the fish swims with the background.(5) Fish show anorthokinesisin optomotor apparatus, their mean swimming speed increasing with the speed of rotation of the background. The precise form of the relationship varies between species and there is also considerable individual variation in performance. Fish accelerate and decelerate relative to the background, fixating on a particular stripe for short periods.(6) Factors limiting the appearance of the optomotor response are contrast, illuminance, acuity, critical flicker fusion frequency and spectral sensitivity.(7) Fish tolerate retinal image movements equivalent to those received when they are carried forwards by the current but not to those received when they are carried backwards. There are ganglion cells in the optic tectum which are sensitive to the direction of movement of targets across the visual field. In the goldfish there are significantly more units sensitive to movements in the temporo‐nasal than in the opposite direction.(8) There are close parallels between the behaviour of fish in schools and in an optomotor apparatus. The optomotor response is apparently innate, occurring in newly hatched fry.(9) Physical and chemical factors can modify rheotaxis. Temperature and olfactory stimuli affect both the sign of the taxis and the kinetic component of the behaviour.(10) Thyroid hormones which are involved in the control of migration have been shown to affect the kinetic component of rheotaxis.(11) Fish show a number of hydrodynamic adaptations to life in currents. Morphological modifications are greatest in fish from torrential streams, which show extreme dorsoventral flattening and have specialized adhesive organs. Other fish select areas of low velocity or decrease their buoyancy with increasing current speed.(12) Rheotropic behaviour plays an important role in the distribution of fish within stream systems, in the maintenance of territory and station and in feeding behaviour. Territory, station and spawning sites in salmonids are all selected in relation to water velocity.(13) Water currents are thought to provide either a transport system or directional clues for fish on migration. The fish either does not respond to the current and is carried passively downstream, or it makes an orientated movement, swimming up‐ or downstream.(14) Eggs and larvae are known to drift passively downstream from their spawning grounds and some adult fish may also drift passively. In the sea both adult and juvenile fish use a form of modulated drift associated with vertical migration. Fish move up into midwater either by direct tidal selection or in relation to the diel cycle of illuminance. In fresh water the downstream migrations of salmonid fry, and smolts under some conditions, occur by modulated drift.(15) There is no evidence that fish migrating in the sea orientate to the current, but in fresh water the upstream migrations of diadromous fish are clearly orientated movements.(16) Water velocity is a major factor for salmonids migrating upstream. For fry it limits the occurrence of upstream migrations and for adults it can also prevent upstream movement. But migrations are often initiated by freshets, and changing water velocity is thought to be the most important factor associated with a freshet.(17) Both environmental and genetic factors affect the direction of migration in relation to the current. In some sockeye salmon fry direction is determined by temperature, but in others the overall direction of movement is genetically determined and environmental factors only modify the behaviour.(18) Rheotropic behaviour has a number of important practical applications in the capture of fish and in guiding them past dams and power stations.(19) The optomotor response plays a basic role in the capture of roundfish by trawls under conditions when the fish can see the gear. Many fish are caught because they become fatigued after a prolonged period of swimming at the same speed as the trawl.(20) Most success in guiding fish away from hazardous areas and bypassing them round dams has been achieved with mechanical barriers which depend on rheotropic reactions of the fish.(21) Louvre screens are very successful in deflecting juvenile salmonids migrating downstream past small dams but are impracticable at large dams. Instead, the turbine intakes are commonly sited at a considerable depth and fish are bypassed by mechanical screens either at the surface of the forebay or into the gatewells immediately upstream of the turbine intakes.(22) With upstream migrants the basic problem is to attract fish to the lower end of the fishways. An adequate ‘attraction velocity’ is an important feature of fishways, which must be sited so that the fish avoid the high velocity discharges from s

ISSN:1464-7931    

DOI:10.1111/j.1469-185X.1974.tb01173.x

出版商:Blackwell Publishing Ltd    

年代:1974

数据来源: WILEY