ISSN:0706-652X    

DOI:10.1139/f82-001

出版商:NRC Research Press    

年代:1982

数据来源: NRC

摘要:

The use of optimization arguments in evolutionary biology has been criticized because the methodology requires an assumption about what is being maximized by natural selection. As optimality arguments are often a priori and always speculative, the critics point out that there is no theoretical basis for any maximization principles in biology. They contend that only empirical work can establish if there are some properties of species that are generally maximized by natural selection. I accept this standard for evaluation, and argue that the concept of surplus power, which provides a physiological basis for optimal foraging and life history theory, is related to fitness. Evidence in the form of specific morphological and behavioral traits in teleost fishes is presented to demonstrate that natural selection has increased surplus power. Life history theory is concerned with how power is allocated by organisms to various vital functions; therefore, the specific problem of stock and recruitment in fisheries can be treated as a special application of life history theory. Some implications about the dynamics and possible survival value of different reproductive strategies exhibited by teleosts are discussed.Key words: surplus power, evolutionary biology, optimal foraging, life history theory, fitness

ISSN:0706-652X    

DOI:10.1139/f82-002

出版商:NRC Research Press    

年代:1982

数据来源: NRC

ISSN:0706-652X    

DOI:10.1139/f82-003

出版商:NRC Research Press    

年代:1982

数据来源: NRC

摘要:

Both temperate and the cold water teleosts are seasonal breeders and production of young fish occurs at an optimal time of the year thereby maximizing survival. Teleost reproductive activity can be divided into annual periods of prespawning, spawning, and postspawning gonadal events which correlate with wave-like endocrine fluctuations. Long-term (circannual) endocrine patterns in the hypothalamo-pituitary-gonad axis (HPG) are observed with maximum hormone levels occurring with spawning and minimal values relating to gonad regression during the postspawning period. Recently, short-term (circadian) endocrine rhythms have also been described. During the period of gonadal recrudescence the basal gonadotropin (GtH) level rises and daily variations of GtH are maximal. Light and temperature variations primarily cue seasonal gonad development in teleosts although the relative importance of these and other environmental triggers differs among various fish species. Clearly HPG activity is influenced by environmental conditions. Temperature has a direct effect upon circulating GtH levels but other physiological mechanisms are implicated as well. Endocrine organ sensitivity undergoes annual variations and cyclic hormone release may respond accordingly. But, daily fluctuations in gonadal responsivity to GtH treatment suggests that phasing of endocrine variations may play an important role and should be considered in future studies of environmental regulation of fish reproductive cycles.Key words: teleost fishes, hormone rhythms, environmental modulation, reproduction

ISSN:0706-652X    

DOI:10.1139/f82-004

出版商:NRC Research Press    

年代:1982

数据来源: NRC

摘要:

Chemical signals (pheromones) have been shown to be involved in schooling, territorial marking, species, sex and individual recognition, courtship, the induction of physiological readiness for mating, and in parent–young interactions. Alarm substances released from damaged skin elicit avoidance behavior. Pheromones may also be involved in homestream recognition in some anadromous species. Most pheromones investigated act as "releasers"; a few "priming" effects have been observed. In most of the chemically mediated interactions surveyed it is not clear that communication in a generally accepted sense is involved, or whether fish are simply responding adaptively to those metabolic products which inevitably "leak" into the environment and only fortuitously provide "information" to conspecifics. In a few cases, specializations in chemical secretions or secretory structures indicate that they have evolved for communication. It is proposed that a combination of factors — the availability of a wide array of soluble biochemical products, the diffuse nature of the sites from which such products might be released, and the lack of strong selection for complex chemical messages — has resulted in the relatively simple "unritualized" systems of chemical communication which appear to be characteristic of fish.Key words: chemical signals, pheromones, reproduction, schooling, homing, parental behavior, fright reaction

ISSN:0706-652X    

DOI:10.1139/f82-005

出版商:NRC Research Press    

年代:1982

数据来源: NRC

摘要:

A number of hormones are known to influence reproductive behavior in teleosts. The best studied in this regard are the sex steroids estradiol and testosterone. Sufficient evidence is available to permit the outlining of possible modes of action of these hormones on mechanisms controlling reproductive responses in fishes. Autoradiographic studies using tritium-labeled steroids have revealed several brain areas with neurons that concentrate testosterone and estradiol in both males and females. An area near the anterior commissure (preoptic region and parts of the area ventralis telencephali) is of primary interest for behavioral systems. Electrophysiological experiments in goldfish (Carassius auratus) have demonstrated that both hormones strongly influence olfactory mechanisms. These effects may be mediated by steroid feedback on brain areas involved in centrifugal control of the olfactory bulbs. The neurological substrates for several behaviors which are thought to be androgen dependent have been studied using classical neurobehavioral methods. These include: spawning and sperm release in goldfish and sunfish (Lepomissp.) and courtship and nestbuilding in sunfish. As of yet, a direct action of sex steroids on these systems has not been demonstrated; however, they all relate to the steroid-concentrating area mentioned above. Some of the systems are incorporated into a tentative model of the neural–hormonal mechanisms controlling reproductive behavior in male goldfish.Key words: reproductive behavior, fishes, brain, hormones, sex steroids, olfaction

ISSN:0706-652X    

DOI:10.1139/f82-006

出版商:NRC Research Press    

年代:1982

数据来源: NRC

摘要:

Gonadotropin releasing hormone (GnRH) activity has been demonstrated in crude extracts of the hypothalamus of several teleost species. Teleost GnRH is similar to the GnRH in elasmobranchs, reptiles, and birds. Luteinizing hormone–releasing hormone (LH–RH) or its superactive analogues stimulate gonadotropin (GtH) secretion in teleosts and can induce ovulation. The actions of LH–RH or its analogues can be self-potentiated or self-suppressed by previous exposure to low and high doses, respectively, and the fish may also be able to modulate its response by other means. There is no agreement on the distribution in the brain of LH–RH immunoreactive perikarya and nerve fibers in teleosts, but the main sites for perikarya are the nucleus lateral tuberis (NLT), preoptic region and telencephalon. Lesioning the NLT by electrical current or monosodium L-glutamate demonstrates that it has functional involvement in the stimulation of GtH release, presumably via GnRH. The NLT and pineal are involved in regulation of daily cycles of GtH secretion, which have importance in stimulating gonadal activity. A GtH release-inhibitory factor (GRIF) apparently originates in the anteroventral preoptic region. Abolition of GRIF action on the pituitary by destruction of its origin or its neural pathways to the pituitary cause very high serum levels of GtH in sexually mature females and males, and ovulation of the females; regulation of the ovulatory surge of secretion of GtH probably involves abatement of GRIF and stimulation by GnRH. Sex steroids have a negative feedback effect during gonadal recrudescence; the greatest negative feedback influence is during the spawning period. In sexually immature fish estrogens and androgens aromatizable to estrogens have a positive feedback effect to stimulate accumulation of GtH in the pituitary; this positive feedback effect may be part of the mechanism of onset of sexual maturity or gonadal recrudescence in teleosts. Binding sites in the brain for sex steroids have been investigated by autoradiography, and active locations were found in the NLT, preoptic region, area ventralis of the telencephalon, and parts of the posterior hypothalamus, as well as the pituitary. The functional significance of most of these binding sites is not known.Key words: teleosts, gonadotropin, gonadotropin releasing hormone, gonadotropin release-inhibitory hormone, steroid feedback, nucleus lateral tuberis, nucleus preopticus

ISSN:0706-652X    

DOI:10.1139/f82-007

出版商:NRC Research Press    

年代:1982

数据来源: NRC

摘要:

Histochemical and ultrastructural data on the cellular source of gonadal steroids are reviewed, together with some recent observations on in vitro steroidogenesis by the ovarian follicles of the amago salmon,Oncorhynchus rhodurus. The interstitial cells of the testis appear to be homologous with mammalian Leydig cells and are considered to be the major site of androgen synthesis. Studies on lobule boundary cells suggest that in some species they may be involved in phagocytosis and transport of metabolites while in others they may be steroidogenic. The granulosa cells and the special thecal cells are the major sites of steroid synthesis in the teleost ovary. Studies on the amago salmon using isolated thecal and granulosa layers indicate that both follicle layers are necessary for estradiol-17β production in vitro in response to salmon gonadotropin. The role of the thecal layer during the major part of vitellogenesis is postulated to be the production of estrogen precursors which are converted to estradiol-17β in the granulosa layer. Histochemical and ultrastructural evidence from a number of species for steroid biosynthesis by postovulatory follicles is supported by our recent radioimmunoassay data from white-spotted char,Salvelinus leucomaenis, and the amago salmon showing that young postovulatory follicles can secrete progesterone; the physiological significance of this observation remains to be explained.Key words: teleosts, gonad, steroidogenesis, in vitro, morphology

ISSN:0706-652X    

DOI:10.1139/f82-008

出版商:NRC Research Press    

年代:1982

数据来源: NRC

摘要:

Very different testicular structures and spermatogenetic patterns have been found in fish of the teleost group. Two types of structures may be identified: (i) a tubular type with no lumen (in cyprinodonts); the cysts migrate from the blind end to the vas efferens during the process of spermatogenesis; (ii) a lobular type having a central lumen receiving the spermatozoa released from cysts which remain stationary along the lobule during spermatogenesis. Different spermatogenetic patterns are distinguished in salmonids and cyprinids. In the latter (carp,Cyprinus carpio, and goldfish,Carassius auratus), some germ cell types (e.g. type B spermatogonia and spermatozoa) are present throughout the year, allowing nearly continuous production of good-quality sperm. Studies of their endocrine patterns suggest that the GTH involved is controlled by external (mainly temperature but also photoperiod) and gonadal factors. The GTH stimulates androgen production and eventually controls spermatogenesis and spermiation. In salmonids, the two major events of the testicular cycle, spermatogenesis and spermiation, are temporally separated by a stage of spermatozoal "maturation" during which the spermatozoa undergo physiological changes. Sperm quality declines during the period of spermiation. The initiation of a new spermatogenetic cycle seems possible only when the spermatozoa have been eliminated from the testis, either by the normal process of spermiation or by intratesticular resorption. This also illustrates the spatial independence of spermatogenesis and spermiation. The endocrine pattern of spermatogenesis in salmonids is similar to that in carp but seems different as regards spermiation. This spermiation process includes two steps, initiation and amplification, which require different GTH levels and steroid balance. Among the steroids, 11-ketotestosterone is the major androgen found in the plasma, but its superiority over other androgens in regard to spermiation remains to be demonstrated. Environmental factors (photoperiodic changes and temperature) may act directly on the central nervous system to control gonadotropin secretion. Temperature may also directly influence the gonad, somatic or germ cells, and steroid metabolism which acts either locally on the gonad or more centrally. The regulation of spermatogenesis in fish appears to be more subtle than previously believed. Major unknowns are whether there is a second GTH and, if so, its site of action; which steroids are directly involved in the control of spermatogenesis in the lobules, and which are the target cells; and which factors regulate testicular size and which pituitary GTH secretion. Finally, the poor yield of spermiation is intriguing and requires further study, considering its practical implication in fish-farming.Key words: spermatogenesis, teleosts, salmonids, cyprinids

ISSN:0706-652X    

DOI:10.1139/f82-009

出版商:NRC Research Press    

年代:1982

数据来源: NRC

摘要:

Chemical data on gonadotropins from several vertebrate species are summarized and discussed from an evolutionary point of view. A high degree of homology has been observed between mammalian gonadotropins (LH and FSH) and thyrotropin (TSH). In non-mammalian species the existence of LH and FSH-like hormones has been demonstrated except for squamate and fish species. Especially in fish the number of GTHs is still controversial. One pituitary glycoprotein assumes various gonadotropic functions of the pituitary, and a second pituitary hormone (carbohydrate-poor) acts on fish ovarian growth. GTHs from bird, reptile, amphibian, and fish pituitaries have been purified and chemically characterized (amino acid composition, carbohydrate content). The existence of a quaternary structure has been demonstrated for several tetrapod LHs and fish GTHs. The amino acid composition of α and β subunits purified from turkey (Meleagris gallopavo), and turtle (Chelydra serpentira,Chelonia mydas) LHs and from common carp (Cyprinus carpio) and sturgeon (Acipenser stellatus) GTHs showed homology with the mammalian α and β subunits. The partial sequences of carp GTH subunits have shown that the carp GTH β was more closely related to mammalian LH β than to FSH β. Hybrid molecules could be obtained by association of heterologous subunits. The kinetics of subunit association has been studied in vitro. As compared to ovine LH, subunit association of carp GTH was more rapid and thermodependent. The subunit β seemed to determine the thermodependence. The various GTH subunits in living vertebrate probably derive from a common ancestral molecule.Key words: vertebrate gonadotropins, chemical characterizations, GTHs subunits, amino acid sequences, hybrid molecules, evolution.

ISSN:0706-652X    

DOI:10.1139/f82-010

出版商:NRC Research Press    

年代:1982

数据来源: NRC