Physiology of Adult Lampreys, with Special Regard to Natural Starvation, Reproduction, and Death after Spawning

摘要: In this review I have attempted to define (1) how the genetic program responsible for migration, sexual maturation, and death after spawning is implemented via the endocrine system, and (2) to what extent environmental factors influence the implementation of the genetic program. The time of upstream migration and the body size at migration may vary enormously (e.g. in Lampetra fluviatilis). Whether the differences reflect different genetic backgrounds in different populations or different environmental conditions in previous stages is unknown. Migration is correlated with lack of food intake, loss of marine osmoregulatory capacity, and atrophy of the intestine. The possible endocrine control of this phase is not clear. Development of secondary sex characters, final maturation of the gonads, spermiation, and ovulation seem to depend on a gonadotropic factor secreted by the pro- and meso-adenohypophysis, but gonadotropin is not as important as in higher vertebrates. Increases in day length or in temperature do not appear to be important clues for initiating sexual maturation; rather this may depend on a metabolic signal related to starvation. The period of natural starvation, from upstream migration until death after spawning, involves atrophy or degeneration in most organs and tissues at the same time as the gonads are developing. With the exception of the intestine and the size of the liver in males, degeneration is generally slow during upstream migration. Upon sexual maturation, the changes are rapid. Energy expenditure and gonadal growth are based on mobilization of lipid and protein, mainly from the body wall. The mobilization of lipid and of protein runs in parallel, both being slow before and rapid during sexual maturation. The possible role of gonadotropin, sex hormones, and insulin in the metabolism of the starving lamprey is discussed. Other hormones seem of little importance. Little is known about the role of the autonomic nervous system in the catabolic processes. Death after spawning can be delayed considerably by hypophysectomy and seems to depend on gonadotropin in females and on some pituitary factor different from gonadotropin in males. Treatment with estradiol surprisingly prolongs life. In all cases of prolonged life induced experimentally, the rate of reduction in body length is slow, probably reflecting a reduced intensity of starvation.Key words: physiology, starvation, reproduction, death, metabolism, migration