摘要:

Amongst the bivalve molluscs, the reproduction of the Chilean oyster,Tiostrea chilensis(Philippi, 1845), is characterised by several unusual features including very low fertility, extremely large eggs and larvae, an extensive period of brooding, and an almost non-existent planktonic larval stage with very limited dispersal. Despite these features being well-described, the gametogenic cycle of this oyster remains poorly understood. It might be expected that the gametogenic cycle ofTiostrea chilensiswould follow the trend toward increasingly labile sexuality that is seen among oyster species with less extensive brooding behaviour. Consequently, the gametogenic cycle in a population of Chilean oysters from north-eastem New Zealand was studied over 20 months from April 1994. Histological preparations revealed that the oysters are protandrous, maturing first as males by about 16 mm in size. From approximately 31 mm some oysters begin to produce ova and oysters over this size are mostly simultaneous hermaphrodites. Eggs and spermatozoa are spawned all year round, although there is a peak of male spawning in late summer-autumn. In contrast to other species of hermaphrodite oysters that brood their larvae, there is no evidence to support the presence of regular alternation of sexes in this population ofTiostrea chilensis.Ripe ova and spermatozoa ark frequently found together in the follicles and are apparently spawned simultaneously suggesting that self-fertilisation is possible (previously true functional hermaphroditism was thought to be very unlikely in the Ostreidae). Overall, the gametogenic cycle in this population ofTiostrea chilensisis dominated by the production and release of spermatozoa in the form of spermatozeugmata. The predominance of spermatogenesis, hermaphroditism and the presence of spermatozeugmata are discussed in relation to the potential difficulty experienced by this oyster in fertilising broods of eggs.

ISSN:0792-4259    

DOI:10.1080/07924259.1998.9652642

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The characterization of photoperiodic induction of sexual rest inArmadillidium vulgarefemales (a cosmopolitan species) shows that the photoperiodic curves relating to the cessation of reproduction are representative of long-days type species. Experiments made on photophase maintenance or reduction show that females are sensitive not only to such reduction but also to its magnitude. Furthermore, the photophase value is relative and depends on previous conditions experienced by the female and there is evidence for the existence of a circannual endogenous cycle inA. vulgare.

ISSN:0792-4259    

DOI:10.1080/07924259.1998.9652643

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The reproductive effort in terms of fecundity and energy allocation was studied in two species of semelparous polychaetes belonging to the genusPerinereis, living in the same environment, with different reproductive modalities. There is a great individual variability both in terms of reproductive effort and fecundity. Fecundity varied from 4080 to 15000 oocytes inP. rullieriand from 7000 to 26000 inP. cultrifera;no linear relationship was found between oocyte number and total jaw length utilised as size index. The energy content of germinal and somatic tissues was determined by Differential Scanning Calorimeter (DSC). The reproductive effort was calculated as RE = EG/(EG+ ES) where EGis the total energy in germinal tissues and ESis the total energy in somatic tissues. Reproductive effort is very high with mean values of 0.62 forP. rullieriand 0.79 forP. cultrifera.The different amounts of energy allocated in germinal tissues can be attributed to the different reproductive modalities—P. rullierireproduces in the atokous phase whereasP. cultriferahas conserved epitoky in its life-cycle. The lack of correlation between reproductive effort and size index strongly suggests that reproductive allocation does not increase with age. In semelparous species the variability in fecundity and reproductive effort observed cannot be interpreted in terms of a trade-off between fecundity and survival as in iteroparous species. In fact, in semelparous an individual allocates all available resources to reproduction and then dies.

ISSN:0792-4259    

DOI:10.1080/07924259.1998.9652644

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Reproductive effort in terms of fecundity and energy allocation was studied in the iteroparous and long lived polychaeteMarphysa sanguinea.Both measures show great variability. Fecundity varied from 8500 to 24300 oocytes; no linear relationship was found between oocyte number and jaw length whereas a direct relationship was established between oocyte number and wet body weight. The energy content of germinal and somatic tissues was determined by differential scanning calorimeter (DSC). The reproductive effort for a single reproductive event was calculated according to the formula: RE = EG/(EG+ ES) where EGis the total energy of the germinal tissues and ESis the total energy of the somatic tissues. The lack of correlation between reproductive effort and size index strongly suggests that reproductive allocation does not increase with age. The reproductive effort ranged from 0.04 to 0.19 with a mean value of 0.120.

ISSN:0792-4259    

DOI:10.1080/07924259.1998.9652645

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The effects of five environmental factors, (i) photoperiod, (ii) temperature, (iii) feeding rate, (iv) population density, and (v) cadmium pollution, on the metagenic life cycle of the hydromedusaEleutheria dichotomawere researched by observing changes in life history. Water temperature, feeding rates and cadmium pollution had significant effects on the medusa generation and changed the relative frequencies of sexuallyversusvegetatively reproducing medusae. Furthermore, the number of brooded planula larvae was affected by cadmium and medusa body size by temperature. Suspected mutational effects of cadmium were not detected. The findings suggest that although development appears to be strongly genetically predetermined, environmental factors can have a significant effect on both the initiation and the reproductive output of sexual reproduction. As a general response to unfavorable environmental conditions the percentage of sexually reproducing medusae as well as the number of brooded planula larvae is increased. The potential indicators of seasonal change, photoperiod and temperature, had no significant effect on the complex life history ofE. dichotoma.The findings suggest that although the life history is sensitive to environmental factorsE. dichotomadoes not take advantage of seasonally changing environmental factors to adapt its life cycle to the particularities of a seasonal environment.

ISSN:0792-4259    

DOI:10.1080/07924259.1998.9652646

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Monthly samples of the shore crabPachygrapsus transversusfrom two distinct annual periods showed that ovigerous females are present throughout the year in the population. However, the relative ovigerous abundance of specimens among sexually mature changes from less than 10% during the winter months to almost 80% in summer. Linear correlations for each year revealed that both temperature and photoperiod were positively associated with relative abundance of ovigerous females. Multiple regression analyses suggested that photoperiod was the main factor affecting breeding in this species. Timing of observed reproductive pattern may enhance larval survival because of particular oceanographic conditions in the study region and favor early juvenile development due to certain species-specific growth features.

ISSN:0792-4259    

DOI:10.1080/07924259.1998.9652647

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

In ovarian follicles ofHyalophora cecropia, [3H]uridine incorporation by germinal vesicles is normally arrested at the start of vitellogenesis when a Ca2+current arises through the intercellular bridges connecting the oocyte to its nurse cells. We show here that the germinal vesicle resumes uridine incorporation following inhibition or reversal of this current. Inhibition/reversal was achieved by treating follicle with any one of three inhibitors that block the Ca2+current by very different mechanisms. Vanadate was used to block Ca2+extrusion by the nurse cells, which drives the current. BAPTA was used to buffer Ca2+activities in the nurse cero, and A23187 was used to increase the membrane conductance of Ca2+. Measurements with ion selective microelectrodes indicated that in all these cases [Ca2+]i in nurse cells equaled or exceeded that in the oocyte; and in all these cases uridine incorporation resumed in the germinal vesicle. Resumption correlated not with the level of [Ca2+] i in the oocyte, but with the absence of a transbridge current from oocyte to nurse cells. Since the current drives an electrical potential gradient that affects the transbridge distribution of soluble proteins, we propose that it tends to prevent transcription promotion factors from reaching the oocyte. This was confirmed by showing that the germinal vesicle also resumes [3H]uridine incorporation following microinjection into oocytes of a centrifugally clarified cytosolic fraction of the nurse cells.

ISSN:0792-4259    

DOI:10.1080/07924259.1998.9652648

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The role of Ca2+in activation and early development of locust eggs was examined through measurement of ooplasmic Ca2+levels before and after fertilization, and through experimental activation of unfertilized eggs. Ooplasmic pCa (i.e. the negative logarithm of Ca2+activity) measured in intact eggs decreased from 5.35 before fertilization, to 4.77 and 3.00 by 1 day and 3 days after fertilization, respectively. pCa was also determined for samples of ooplasm collected by rupturing eggs under paraffin oil. The pCa was 5.10 in ooplasm isolated from unfertilized eggs, and 3.84 in ooplasm collected from eggs within 4 h of fertilization. Ooplasmic pCa remained between 3.97 and 3.12 from 1–6 days after fertilization. Since a decline in pCa indicates an increase in ooplasmic Ca2+activity, the data suggest that regulation of ooplasmic Ca2+during post-fertilization development involves release of Ca2+from internal stores. Experimental egg activation was examined in eggs dissected from the oviducts before fertilization and incubated on moist filter paper. Some eggs were first immersed in experimental solutions for 30–60 minutes before incubation. The presence of an embryo 2 or 4 days after fertilization or experimental treatment was used as an indicator of egg activation. Activation occurred in 92% and 12% of fertilized and untreated eggs, respectively. The percentage of unfertilized eggs which activated increased to 47% if eggs were soaked 30–60 minutes in physiological saline, and to as much as 65%-68% if eggs were injected withCa2+buffers or if a Ca2+action potential was evoked. Up to 36% and 42% of unfertilized eggs activated after incubation in Ca2+-free salines or in the presence of the Ca2+-channel blocker Cd2+, respectively. Taken together, the results suggest that entry of external Ca2+through voltage dependent channels increases the proportion of eggs which activate, but is not an absolute requirement for activation.

ISSN:0792-4259    

DOI:10.1080/07924259.1998.9652649

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The sex-ratio and behavioural mating peculiarities ofTetraneura nigriabdominalishave been investigated. A morphological study by SEM revealed the developmental stages of sex-attractant pheromone glands on the hind tibiae of females, the morphology of the chemiosensilla on the male antennae, and peculiar microsculptures on abdominal stemites which may be interpreted as an anchorage system favouring copulation.

ISSN:0792-4259    

DOI:10.1080/07924259.1998.9652650

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The cephalic vesicles of the immature endo-ectoparasitic larvae ofGonatopus camelinusKieffer andGonatopus clavipes(Thumberg) were studied using light and electron microscopy. The vesicles appear as hollow evaginations of the cephalic body wall and their tegument consists of a monolayered epithelium externally surrounded by a permeable cuticle. In the first larval instars, the epithelial cells are pyramid-shaped and separated by large intercellular spaces. In the last larval instars they are polyhedral and the intercellular spaces are no longer evident. The vesicles have no connection with the gut of either the host or the larva. These data suggest that nutrients are absorbed by the dryinid larva from the haemolymph of the host through the permeable surface of the cephalic vesicles, where they are stored in the lumen and enter the larval haemolymph without passing through the gut. In all immature larval instars the mouth is closed.

ISSN:0792-4259    

DOI:10.1080/07924259.1998.9652651

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor