摘要:

In the giant African snail,Achatina fulica, the ultrastructure of the dorsal bodies was examined in an attempt to characterize the neural control of their activity. In the dorsal body many large ellipsoidal lipid droplets with a thick electron-dense cortex and secretory granules with an electron-dense core were found. In a bundle of commissural nerves that originated from the cerebral ganglion, two types of axon were detected: type I axons contained spherical granules and type II axons contained ellipsoidal granules. These axons innervated the dorsal body cells. Our results suggest that each cell of the dorsal bodies is under the control of two axons from the cerebral ganglion: one that is stimulatory and another that may be inhibitory.

ISSN:0792-4259    

DOI:10.1080/07924259.1994.9672374

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The insect prothoracic gland is an ecdysteroidogenic (molting hormone) structure that under the control of a brain neuropeptide is responsible for the surges in ecdysteroid titer required for cellular reprogramming, molting and metamorphosis. The glands are stimulated by the brain neurohormone via a signal transduction cascade that involves cAMP, Ca2+/calmodulin and protein kinases. Since the precision of the ecdysteroid surge is vital for the coordination of those biochemical processes encompassing molting, an investigation was initiated to provide basic information for a future analysis of how the 200–250 cells of theM. sextaprothoracic gland communicate to assure a rapid, uniform and temporally correct surge of ecdysteroids. An analysis of gap junctions between cells of the prothoracic glands was undertaken using scanning (SEM) and transmission electron microscopy (TEM) as well as freeze fracture. The SEM data revealed that during the fifth larval instar the cell size, shape and surface morphology underwent dramatic changes, e.g., the cell size increased from 30–40 μm in diameter on day 1 to about 65 μm on day 7. In addition, there was the development of cell-to-cell major connecting areas and intercellular bridges. TEM analysis demonstrated that both the major connecting areas and intercellular bridges contain interdigitating cellular processes from neighboring cells. Typical gap junctions are distributed in an organized manner, occurring on limited portions of the cell membrane, with preferential localization close to the distal ends of these processes. They are septilaminar structures with a central cleft 2–3 nm wide and electron-dense strata that appear to be symmetrical. Numerous multilamellar bodies are often seen in these areas. The size and frequency of both gap junctions and multilamellar bodies appear to be correlated with the developmental stage and physiological state of the insect. Freeze fracture images of the region of contact between interdigitating processes reveals clusters of particles on the E face. These clusters represent gap junctions and are similar to gap junction clusters reported for other insect tissues. The clusters are often irregular in shape, and the particles are always randomly arranged. Many of the particles are elongated, suggestive of dimers or the bridging of adjacent particles, and these elongated particles are matched by a corresponding pattern of pits found on the P face. These gap junctions may promote the synchronization of secretory activity of the cell comprising the prothoracic glands.

ISSN:0792-4259    

DOI:10.1080/07924259.1994.9672375

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Quantities of protein-milk, glycogen and phosphorylase activity were measured in brood sacs of the cockroachDiploptera punctatato understand how competence to synthesize milk is achieved. The time interval between oviposition and the first occurrence of milk in the brood sac (milk synthesis), as detected by rocket immunoelectrophoresis, was the same in the first two reproductive cycles of mated females and in those virgins that oviposited. The test for competence was the ability of non-milk-producing brood sacs to synthesize milk after implantation into hosts actively secreting milk. As previously shown for first cycle females, competence in second cycle females and virgins always began at constant intervals after oviposition and before milk synthesis. Quantification of glycogen in the brood sac throughout the first reproductive cycle revealed glycogenolysis at the onset of competence and during advanced milk production. Glycogenolysis at competence also occurred in brood sacs of second cycle females. However, in fat body glycogenolysis occurred only during late milk production, Decapitation after oviposition did not alter glycogenolysis at competence. The greatest concentration of total glycogen phosphorylase activity in the brood sac (activity/brood sac protein) occurred at competence. Thus egg development and oviposition appear to determine the timing of competence and milk production, causing the release of a signal that mobilizes glycogen as it prepares the brood sac for milk synthesis.

ISSN:0792-4259    

DOI:10.1080/07924259.1994.9672376

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The sex differentiation of the crabEriocheir japonicuswas studied histologically and morphologically from the first zoeal stage to the fifth crab stage. The gonoducts were the first sexual characteristic that underwent sex differentiation. As early as the crab was at the megalopa stage, gender could be determined on the basis of two different orientations of the gonoducts. One orientation was toward the eighth thoracic sternite in the males and the other was toward the sixth thoracic sternite in the females. The second sexual characteristic that underwent sex differentiation was found in the pleopods at the third crab stage. No remarkable morphological or structural difference was observed between the gonia in males and those in females. We compared our findings with those in the crabs studied in previous research regarding the sequences of the sex differentiation of sexual characteristics and the development of gonoducts and gonopores. We also discussed the timing of the appearance of the androgenic gland in the sex differentiation of decapods and other malacostracans. Unlike isopods and amphipods, no androgenic gland is visible prior to sex differentiation inE. japonicus.This finding is consistent with those reported in other decapods. We hypothesize that in decapods, before the androgenic gland cells form a gland, they already exist dispersively in both sexually undifferentiated genetic males and females. In the genetic males, these dispersive androgenic gland cells may be activated by the male sex-determining genes to produce androgenic gland hormones inducing sex differentiation.

ISSN:0792-4259    

DOI:10.1080/07924259.1994.9672377

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

We describe the external and internal morphology of intersexGammarus duebenifrom Budle Bay, Northumberland and present the first scanning electron micrograph of the external morphology of an intersex. The pattern of intersex expression in this population differs from that previously described in a German population: intersexes are more frequent in the UK population; and all conform to the intermediate form of the intersex types described in the German population. Such a contrast between populations has not previously been described and may provide a tool to understand the phenomenon. The distribution of a feminizing microsporidian is examined. However, parasitism is not the main agent of intersexuality.

ISSN:0792-4259    

DOI:10.1080/07924259.1994.9672378

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The solitary egg-larval parasitoids of the genus Chelonus have the unique effect of inducing in their lepidopterous hosts the precocious onset of metamorphosis and developmental arrest in the precocious prepupa. As a prerequisite to identifying the physiological and biochemical mechanisms underlying these developmental effects, we analyzed the morphology and various growth parameters in the course of development ofChelonus inanitusand studied the effect of this parasitoid on growth and development of its hostSpodoptera littoralis.

ISSN:0792-4259    

DOI:10.1080/07924259.1994.9672379

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

FertileDrosophila subobscuramales having the X chromosomal gene arrangement A2+3+5+7produce predominantly female offspring. These males are called “sex ratio” males. Irrespective of the unisexual offspring, the total number of offspring of a sex ratio male can be as high as the bisexual offspring of control males. Thus the absolute number of female offspring is higher in A2+3+5+7males than in control males. One reason for this high number of female offspring could be increased sperm production by sex ratio males. In the present study we analyzed spermatogenesis of sex ratio and control males. Sperm differentiation inDrosophilaoccurs in so-called cysts. InD. subobscurathey contain, after spermatogonial divisions and meiosis, 128 synchronously developing spermatids each. We found that the testes of sex ratio males contained double the amount of cysts as control males. However, this is not the explanation for the great amount of female offspring of those males. In the final stage of spermatid maturation, in the coiling stage, the number of cysts was the same in sex ratio males as in control males. Because in sex ratio males only the X sperm are released into the seminal vesicle, these males transfer only half the number of functional sperm. The mechanism which is in charge of the high female offspring of sex ratio males could be a higher frequency of copulation and/or a better utilization of sperm by the female, or something else. The same high cyst number as in fertile A2+3+5+7males was also found in sterile males with the same A chromosomal gene arrangement but different autosomal gene arrangements as fertile A2+3+5+7males. This result indicates that the total number of cysts is controlled only by the A chromosome, independent of male fertility. In sterile A2+3+5+7males sperm differentiation stopped during individualization. No sperm was found to enter the seminal vesicle.

ISSN:0792-4259    

DOI:10.1080/07924259.1994.9672380

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The biogenic monoamines—serotonin, dopamine and noradrenaline—were determined by fluorometric techniques in ganglia, gills and gonads ofArgopecten purpuratusat different times after spawning. The temporal course of these amines was analyzed separately for the first 24 h and for the period when gonad was recovering from spawning and gametogenesis was proceeding. The levels of the three amines were always higher in ganglia than in gills or gonads. Noradrenaline was the least abundant in all the tissues analyzed. Serotonin and dopamine levels were always higher in the male gonadal portion than in the female portion. Neither of the amines changed their values in ganglia during the first day after spawning, but levels of noradrenaline in gills decreased significantly during this period. Except for noradrenaline in the male portion, the content of the three amines decreased significantly in the gonads during the first hours after spawning. During gonadal recovery, ganglionic levels of the three amines increased, and the day before a new spawning they attained a high value. The amines in gills showed variable levels during this period. In the middle of the process of active gametogenesis, the gonadal levels of serotonin and noradrenalin increased and then decreased towards the end of that period. A possible regulatory role of monoamines on the gametogenic process through substrate mobilization, via the stimulation of glycogenolysis by cyclic AMP, is proposed.

ISSN:0792-4259    

DOI:10.1080/07924259.1994.9672381

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

ISSN:0792-4259    

DOI:10.1080/07924259.1994.9672382

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

ISSN:0792-4259    

DOI:10.1080/07924259.1994.9672373

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor