Post-embryonic development in the ventral cord of Caenorhabditis elegans.

56 nerve cells are added to the ventral cord and associated ganglia of Caenorhabditis elegans at about the time of the first larval moult. These cells are produced by the uniform division of 13 neuroblasts followed by a defined pattern of cell deaths. Comparison with the data in the previous paper suggests that there is a relationship between the ancestry of a cell and its function. The significance of programmed cell death is discussed.     

Embryonic development clarifies polyphyly in ostracod crustaceans

The present study describes the embryonic developmental process of the bioluminescent ostracod crustacean Vargula hilgendorfii . Optical microscopy, scanning electron microscopy, DAPI staining and video recording were used for observations. This study is the first detailed report of the embryonic development of a myodocopid ostracod. Contrary to previous studies, cleavage occurred in the yolk sphere and no evident cleavage furrow was found. No nauplius stage was found, and five pairs of appendages developed simultaneously. A bivalved carapace developed from two independent buds of the carapace valves. The buds of the left and right valves are enlarged, and become combined. The combined 'one-piece' carapace was divided by the formation of a hinge, and the usual bivalved carapace was formed. On the 16th day, embryos hatched as juveniles with six pairs of appendages, a pair of immature appendages, a pair of compound eyes, a median eye and a bivalved carapace. An important suggestion for the classification of Ostracoda is derived from the observed development of appendages and carapace, because the subclass Ostracoda is defined mainly by the similarities of appendages and the bivalved carapace. The present observations clearly show that the developmental process of Myodocopa differs from that of Podocopa, and supports polyphyly of the Ostracoda.     

Post-embryonic development of amphipod crustacean pleopods and the patterning of arthropod limbs

Morphology and post-embryonic development of the pleopodal rami of the amphipod crustacean Gammarus roeselii Gervais, 1835 are described, with particular reference to the differentiation of limb articles. An article is the part of a limb between two complete arthrodial membranes and, in the pleopodal rami, most arthrodial membranes are accompanied by two plumose setae on the opposite faces of the article. During post-embryonic development, the rami acquire new plumose setae and new arthrodial membranes proximal to the already differentiated part; this implies that new articles are produced by the division of the most proximal article only. On the proximal article of the inner ramus there are also some bifid setae, whose number increases post-embryonically, most likely by proximal addition of new setae. Data from different limb types of different arthropod groups suggest that during post-embryonic development new articles are also produced from one or more specific zone(s) of the limbs. General aspects of these “growth zones” in arthropod limbs are discussed and their distribution, in respect to both different limb types and different taxa, is reviewed. The available data do not allow unambiguous conclusions about the evolution of growth zones and limb patterning, but the most relevant questions are nevertheless outlined.     

Post-embryonic development of water- and airbreathing organs of Anabas testudineus (Bloch)

The development of respiratory surfaces in post-embryonic stages of Anabas testudineus was studied using morphometric methods on serial sections through the pharyngeal region of specimens obtained by induced breeding of known parentage. The larvae and fry were fixed in glutaraldehyde and osmium tetroxide. In the young stages aquatic respiration was found to be obligatory. The hatchlings come out of the egg membranes about 10 h after fertilization. During the yolk-sac stages gaseous exchange takes place through the well vascularized skin. The gills start differentiating at about 24 h and become functional at about 39 h. The labyrinthine organs begin to develop after 51 h but the hatchlings do not take an air breath until they reach 13–14 days. The appearance of scales at 11–14 days probably hinders cutaneous respiration and is correlated with the onset of aerial respiration.
Morphometric analysis using stereological methods shows high surface: volume ratios for the gills and labyrinthine organs as adaptations to gas exchange function. A marked decrease in surface: volume ratio for the suprabranchial cavities between 7 and 11 days indicates an increase in volume to accommodate the expanding labyrinthine plates which retain a fairly constant surface: volume ratio.     

Post-embryonic development of chicks of the Japanese quail under conditions of the limited volume

According to our results, chicks of the Japanese quail can survive within the first 10 days of a life under conditions of the limited volume when their mobility is completely limited. However, their development was impaired in comparison with chicks housed in the common cages. Besides, the delay in development of chick's plumage has been observed. The analysis of body mass in test groups has shown that practically all chicks were smaller than chicks from control group. It is the result of feed consumption decrease (about 30% from control group) caused by the restriction of mobility of chicks. But after their transferring to the common cages at the end of the experiment, body mass in test group rapidly reached the level of body mass in control group. Research has shown that percent of alive of quail chicks maintained in the chamber of animals of complex "Incubator-2", was higher than in first two experiments. Therefore, works on improvement of devices for the maintenance of quail chicks continue, and also new adaptations develop for the maintenance of chicks in their early post-embryonic period (till 10 days) with reference to conditions of weightlessness.     

Post-embryonic development of cyclopoid copepods in various seasons at Lake Balaton (Hungary)

The development, generation number and diapausing state of threeCyclops species dominant in the open water of Lake Balaton werestudied by means of vials placed back into the lake, in naturalfeeding conditions. The males of all three species turned intoadults earlier than the females. The copepodite V stage wasof the longest duration. Three generations of Cyclops vicinusdeveloped yearly; in spring, autumn and winter. About 50% ofthe copepodite stage IV of the spring generation entered activediapause at the end of May, beginning of June, then entereddormancy between the middle of June and middle of July. Consideringthe literary data as well, it seems that the generation numberof the species is the function of temperature and of the water'strophic state. The Acanthocydops robustus f. limnetica is fondof warm water (> 14°C). Seven generations of this speciesdeveloped completely yearly, during an average of 2-week intervalsbetween May and September. The eightli generation died in thenaupliar stage. The generation number of A. robustus f. limneticadepends on the average temperature of the lake. Inactive diapausecould not be observed for this species. Only one generationof Mesocyclops latckarti developed in autumn. The copepoditeV of the winter generation entered active diapause below a watertemperature of 10°C, and inactive diapause from the endof January, which state ended in March.     

Post-embryonic functions of HSP90 in Tribolium castaneum include the regulation of compound eye development

Heat shock protein 90 (HSP90) belongs to a family of conserved chaperons with multiple roles in stress adaptation and development, including spermatogenesis, oogenesis and embryogenesis in insects. In the red flour beetle, Tribolium castaneum, we found that HSP90 is transiently upregulated during larval development, in prepupae, in female pupae and in adults, suggesting multiple post-embryonic roles. We found that silencing HSP90 expression by RNA interference was lethal within 10 days at all developmental stages. Titration experiments revealed that larvae were more susceptible than pupae or beetles. Interestingly, HSP90 silencing in final instar larvae resulted in abnormal pupal phenotypes lacking compound eyes and exhibiting prepupal features, suggesting developmental arrest at the prepupal stage. Our results suggest that HSP90 functions can be expanded beyond the known ones in insect embryogenesis to include roles in post-embryonic development such as the regulation of compound eye development.     

Post-embryonic development of circadian rhythm in the cricket,Gryllus bimaculatus: A rhythm reversal

Summary Locomotor activity of the male cricketGryllus bimaculatus DeGeer was recorded from the 7th or last (8th) instar nymph. The nymph showed a diurnal rhythm (nymphal rhythm = NR), while the adult, on the contrary, was nocturnal (adult rhythm = AR) (Fig. 1). This rhythm reversal occurred suddenly 3 to 5 days after the imaginal molt, almost simultaneously with the first spermatophore formation and the start of stridulation (calling song) (Fig. 2). In addition to the antiphase relationship, both rhythms also differed in the freerunning period (tau) and wave form. Tau_scdd was significantly longer in NR (24.33 h) than in AR (23.91 h) (Fig. 3). AR was characterized by a sharp activity peak in each cycle, which NR, however, lacked (Fig. 1, 3, 6). On the basis of these differences, two possibilities are discussed; one is that NR and AR are separate oscillations and the other is that both are coupled to different phase points of one oscillation.Abbreviations LD light dark - DD constant darkness - LL constant light - NR nymphal rhythm - AR adult rhythm     

广东鲂的胚后发育

2007年6~7月,在西江肇庆江段收集广东鲂(Megalobrama hoffmanni)亲鱼,通过人工催产、干法授精获得受精卵。随后对其胚后发育进行连续观察,拍照并详细描述各发育期形态。广东鲂胚后发育的主要特征是:身体较为透明,头部背面色素最多时达7~8个;听囊前后色素蔓延成明显的色素花;腹部前端逐渐形成葫芦状的色素花纹,该花纹在腹鳍芽出现后逐步淡化、消失;尾长占全长的比例较大,从孵出期时的31%逐渐增加到臀鳍形成期时的46%;鳔一室期后,鱼苗身体肌节数为43对左右,其中尾部肌节数19对以上。经过24d的生长和发育,鱼苗各鳍条基本形成,形态与成鱼相似。     

Post-embryonic genesis of bursal follicles in the duck

The structural and histological characteristics of the limiting layer between the cortex and medulla of the bursa of Fabricius in the duck are described in relation to different functional moments of the organ. On E.M. study the limiting layer, in duck having 30 days of age, is constituted of reticular-epithelial cells palisades in shape with many cytoplasmics extension. Lymphatic migration occur in interstitial spaces.     

Post-embryonic development of Psammopsyllus maricae Cottarelli,Saporito & Puccetti, 1983 (Copepoda,Harpacticoida)

The post-embryonic development of Psammopsyllus maricae Cottarelli, Saporito & Puccetti, 1983 has been described for the first time. Six morphologically distinct naupliar and five copepodid stages were discerned and studied using light microscopy. Some features were also examined by scanning electron microscopy.     

Post-embryonic larval development and metamorphosis of the hydroidEudendrium racemosum (Cavolini) (Hydrozoa,Cnidaria)

The morphology and histology of the planula larva ofEudendrium racemosum (Cavolini) and its metamorphosis into the primary polyp are described from light microscopic observations. The planula hatches as a differentiated gastrula. During the lecithotrophic larval period, large ectodermal mucous cells, embedded between epitheliomuscular cells, secrete a sticky slime. Two granulated cell types occur in the ectoderm that are interpreted as secretory and sensorynervous cells, but might also be representatives of only one cell type with a multiple function. The entoderm consists of yolk-storing gastrodermal cells, digestive gland cells, interstitial cells, cnidoblasts, and premature cnidocytes. The larva starts metamorphosis by affixing its blunt aboral pole to a substratum. While the planula flattens down, the mucous cells penetrate the mesolamella and migrate through the entoderm into the gastral cavity where they are lysed. Subsequently, interstitial cells, cnidoblasts, and premature cnidocytes migrate in the opposite direction, i.e. from entoderm to ectoderm. Then, the polypoid body organization, comprising head (hydranth), stem and foot, all covered by peridermal secretion, becomes recognisable. An oral constriction divides the hypostomal portion of the gastral cavity from the stomachic portion. Within the hypostomal entoderm, cells containing secretory granules differentiate. Following growth and the multiplication of tentacles, the head periderm disappears. A ring of gland cells differentiates at the hydranth's base. The positioning of cnidae in the tentacle ectoderm, penetration of the mouth opening and the multiplication of digestive gland cells enable the polyp to change from lecithotrophic to planktotrophic nutrition.     

Thermal behaviour of crustaceans

Specific thermoreceptors or putative multimodal thermoreceptors are not known in Crustacea. However, behavioural studies on thermal avoidance and preference and on the effects of temperature on motor activity indicate that the thermosensitivity of crustaceans may be in the range 0.2-2 degrees C. Work on planktonic crustaceans suggests that they respond particularly to changes in temperature by klinokinesis and orthokinesis. The thermal behaviour of crustaceans is modified by thermal acclimation among other factors. The acclimation of the critical maximum temperature is an example of resistance acclimation, while the acclimation of preference behaviour may be classified as capacity acclimation of some other function. In crustaceans, the use of the concepts stenothermy and eurythermy at the species level is questionable, and it is not possible to divide crustacean species into thermal guilds as suggested for fishes. Thermal preference behaviour contributes to fitness in different ways in different species, often by maximising the aerobic metabolic scope for activity. In crustaceans the peripheral nervous system seems to have retained the capacity for thermosensitivity and thermal acclimation independently of the central nervous system control of behaviour.     

The ontogenetic development of refracting superposition eyes in crustaceans: Transformation of optical design

We have investigated, comparatively, the ontogenetic development of the compound eye in larvae of a mysid (Neomysis) and a euphausiid (Thysanoessa) species and found it to be close to identical in the two species. The larval eye is of apposition type with special adaptations for planktonic life. The elongated dioptric apparatus is devoid of screening pigment and instead has a proximal lens optically isolating the ommatidium. The pigmented retina is extremely compressed making the eye largely transparent and presumably suitable for a planktonic life. The presence of this specialized type of eye in the planktonic larvae of euphausiids was known before but it is intriguing to find exactly the same type in mysids, spending their entire larval life as embryos in the female marsupium. A possible explanation is offered if mysids earlier in evolution had planktonic larvae. Upon reduction of free-living larvae, the transparent type of eye may have been preserved because there is no selection pressure on the larva to change it. In late larval life, both species transform their eyes to a refracting superposition type typical for adult mysids and euphausiids. The process of transformation and the functional connection between transparent apposition and superposition is described.     

Post-embryonic cell lineages of the nematode,Caenorhabditis elegans

The number of nongonadal nuclei in the free-living soil nematode Caenorhabditis elegans increases from about 550 in the newly hatched larva to about 810 in the mature hermaphrodite and to about 970 in the mature male. The pattern of cell divisions which leads to this increase is essentially invariant among individuals; rigidly determined cell lineages generate a fixed number of progeny cells of strictly specified fates. These lineages range in length from one to eight sequential divisions and lead to significant developmental changes in the neuronal, muscular, hypodermal, and digestive systems. Frequently, several blast cells follow the same asymmetric program of divisions; lineally equivalent progeny of such cells generally differentiate into functionally equivalent cells. We have determined these cell lineages by direct observation of the divisions, migrations, and deaths of individual cells in living nematodes. Many of the cell lineages are involved in sexual maturation. At hatching, the hermaphrodite and male are almost identical morphologically; by the adult stage, gross anatomical differences are obvious. Some of these sexual differences arise from blast cells whose division patterns are initially identical in the male and in the hermaphrodite but later diverge. In the hermaphrodite, these cells produce structures used in egg-laying and mating, whereas, in the male, they produce morphologically different structures which function before and during copulation. In addition, development of the male involves a number of lineages derived from cells which do not divide in the hermaphrodite. Similar postembryonic developmental events occur in other nematode species.     

Post-embryonic development of the Furongian (late Cambrian) trilobite Tsinania canens: implications for life mode and phylogeny

SUMMARY The current concept of the order Asaphida was proposed to accommodate some Cambrian and Ordovician trilobite clades that are characterized by the possession of a ventral median suture. The family Tsinaniidae was recently suggested to be a member of the order Asaphida on the basis of its close morphological similarity to Asaphidae. Postembryonic development of the tsinaniid trilobite, Tsinania canens , from the Furongian (late Cambrian) Hwajeol Formation of Korea, reveals that this trilobite had an adult-like protaspis. Notable morphological changes with growth comprise the effacement of dorsal furrows, sudden degeneration of pygidial spines, regression of genal spines, and loss of a triangular rostral plate to form a ventral median suture. Programmed cell death may be responsible for degenerating the pygidial and genal spines during ontogeny. Morphological changes with growth, such as the loss of pygidial spines, modification of pleural tips, and effacement of dorsal furrows, suggest that T. canens changed its life mode during ontogeny from benthic crawling to infaunal. The protaspid morphology and the immature morphology of T. canens retaining genal and pygidial spines suggest that tsinaniids bear a close affinity to leiostegioids of the order Corynexochida. Accordingly, development of a ventral median suture in T. canens demonstrates that the ventral median suture could have evolved polyphyletically, and thus the current concept of the order Asaphida needs to be revised.