Embryogenesis and larval development of migratory matrinchã Brycon orthotaenia Günther 1864 (Characiformes: Bryconidae)

The present study aimed to characterize the embryogenesis and larval development of matrinchã (Brycon orthotaenia), through the analysis of egg and larval morphology. Fertilized eggs had a mean diameter of 1.17 mm, with yolk occupying most of the egg (1.06 mm). Embryogenesis lasted for 15 hr at an average temperature of 27°C. At hatching, yolk-sac larvae measured 3.67 mm in mean standard length (SL). Pre-flexion, flexion and post-flexion larva had 5.01, 8.24 and 11.88 mm mean SL, respectively, with significant increases observed particularly in head length, head height, and eye diameter. The yolk persisted in the yolk-sac and pre-flexion stages (5.96 mm SL). The mouth opening could first be observed 13 hr after hatching, and cannibalism was observed 29 hr after hatching in pre-flexion larvae after absorption of the yolk sac; in such cases, the larvae had already developed teeth and a complete digestive tract. For an endangered species such as matrinchã, early life history studies are important because they provide researchers with a better understanding of critical stages of development and thus enhance captive management by rearing and restocking of the species.     

Ultrastructure aspects of Brycon gouldingi (Teleostei,Characidae) related to swimming ability and feeding during larval development

The larval ultrastructure of Brycon gouldingi related to swimming and feeding from hatching to total yolk absorption is described from scanning electron micrographs. Newly hatched larvae (time zero) had no mouth opening, undefined optic vesicles, an olfactory plate visible as a shallow depression, rudimentary gill arches, neural groove, embryonic fin and a primary neuromast in the dorsal region of the head. At the time of yolk absorption, 55 h post hatching, the larvae presented an optic vesicle comprising an optic cup and crystalline lens; a mouth with tongue, tapered teeth and taste buds; a ciliated olfactory cavity; branched gill arches; filled neural groove signalling central nervous system development; caudal, pectoral, dorsal and anal fins; and neuromasts distributed throughout the head and body. These characters are related to prey capture and swimming ability, key aspects of survival during the larval stage. The results of this study provide important information for exploitation and aquaculture of B. gouldingi.     

The club‐shaped gland of amphioxus: export of secretion to the pharynx in pre‐metamorphic larvae and apoptosis during metamorphosis

In amphioxus larvae, the club‐shaped gland is a tube connecting the pharyngeal lumen with the external environment. The functions of the gland and its fate during the larva‐to‐juvenile metamorphosis have long been controversial. Here we use a fixative including ruthenium red to preserve extracellular secretions (presumably glycoproteins) in late pre‐metamorphic larvae. This procedure reveals reddish, fibrogranular material in the lumen of the club‐shaped gland and in the pharynx adjacent to the gland's inner opening. This finding strengthens the idea that secretions of the club‐shaped gland are exported to the pharyngeal lumen to help form a mucous trap for capturing food particles entering the mouth. We also use the terminal desoxynucleotidyl transferase‐mediated dUTP nick end labelling (TUNEL) assay to study apoptosis in the tissues of metamorphosing larvae. One of the earliest events of metamorphosis is the massive apoptotic destruction of the club‐shaped gland. Therefore, despite some previous opinions to the contrary, the cells of the gland do not survive to participate in the genesis of the definitive endostyle or any other post‐larval structures.     

Vertical transmission of nucleopolyhedrovirus in the silkworm, Bombyx mori L

Nucleopolyhedrovirus (NPV) was tested for vertical transmission in the silkworm, Bombyx mori. Fifth instar larvae were exposed to four different dosages of BmNPV (830, 1300, 1800, and 2000OBs/larva) and a dosage of about 2000OBs/larva was found suitable for obtaining infected adults. Histopathological studies revealed the infection in susceptible tissues and organs initially, and at later stages of infection cycles the spermatocytes and nurse cells in the young oocytes were infected in the larval rudiments of testis and ovary, respectively. The mating of infected females with uninfected males resulted in significant reduction in fecundity (P < 0.01) and hatching of eggs (P < 0.001) due to transovarial transmission of BmNPV. Mating tests of uninfected females and infected males also confirmed venereal transmission as there was a significant reduction in hatching of eggs (P < 0.01). Further, among the F1 hybrid offspring (infected female x uninfected male) that were infected transovarially, larval progeny died at first and second instar stages, whereas those infected venereally developed acute lethal infection late and died by the end of third and fourth instar stage. PCR amplification and sequencing of 473bp of immediate early-1 (ie-1) gene of BmNPV isolated from the viral-infected parent and the F1 offspring confirmed that the viral infection is vertically transmitted to the progeny.     

不同食料植物对美国白蛾生长发育和繁殖的影响

2010年6月至7月,在室内研究了美国白蛾Hyphantria cunea(Drury)第1代幼虫对洋白蜡、欧美107号杨、法桐和白榆的取食量及不同的食料种类对美国白蛾生长发育和繁殖的影响。结果表明,美国白蛾对受试的各树种的取食量以洋白蜡为最多,完成一代平均每头可以取食2.21 g,其次为欧美107号杨1.95 g,再次为法桐和白榆,分别为1.85 g/头和1.68 g/头。3龄后幼虫对不同的寄主呈现出一定的偏好性,特别是5龄和6龄幼虫对不同的寄主的取食量表现出显著差异。不同的食料植物对美国白蛾幼虫和蛹的发育历期、存活率、蛹重、成虫寿命、产卵量等有显著影响。取食法桐对其生长发育和繁殖表现出明显的不利性,主要表现为幼虫期延长、蛹重减轻、单雌产卵量降低。     

Differential replication of ribosomal DNA during larval development in Calliphora (Diptera)

The hybridization of ribosomal RNA with DNA extracted from whole insects has been compared at six stages during the development of the blowfly Calliphora stygia. Total DNA from hatching larvae contains approximately 20% more rDNA than does total DNA from either mid-embryonic or adult insects. DNA from late third-instar larvae close to pupariation contains about 30% less rDNA than that from hatching larvae. The proportion of rDNA to total DNA in larvae of intermediate ages falls between these two extremes. Ribosomal RNA cistrons are thus replicated more rapidly than the remainder of the genome in the late embryonic or earliest larval stages, but more slowly during the later cycles of DNA synthesis in those larval tissues which develop high levels of polyteny.     

Induction of metamorphosis in the sand dollar Peronella japonica by thyroid hormones

The larva of the sand dollar Peronella japonica lacks a mouth and gut, and undergoes metamorphosis into a juvenile sand dollar without feeding. In the present study, it was found that thyroid hormones accelerate the metamorphosis of P. japonica larvae. The contents of thyroid hormones in larvae increased gradually during development. Thiourea and potassium perchlorate, inhibitors of thyroid hormone synthesis, delayed larval metamorphosis and simultaneously repressed an increase in the content of thyroxine in the larval body. These results suggest that the P. japonica larva has a system for synthesis of thyroid hormones that act as factors for inducing metamorphosis.     

Peculiarities of ultrastructural organization of the metathoracic ganglion in the locustLocusta migratoria larva

In electron microscopic study of structural organization of the thoracic ganglion of the locust larva of the 1st age (1–2 days after hatching), the data on the structure of motoneurons of the 1st nerve, basal and motor neuropil of the larva were obtained. The effector elements of the larval locust CNS are formed rather early and have the structural plan similar to that in adult insects. However, in the larval motoneurons innervating the flight muscles (longitudinal dorsal muscles, wing depressors) the clearly seen features of immaturity of these nervous elements are revealed. Study of the larval ganglion neuropil has shown that the basal neuropil is morphologically formed sufficiently completely as early as in larvae of the first days after hatching. There are shown longitudinal contacts between axons of the ventral neuropil zone, the presence of axons forming theen-passant contacts as well as the synapses with a heterogeneous set of vesicles in the presynaptic area. The presence of the great number of granular vesicles in the basal neuropil of the locust larva may indicate an important role of catecholamines in the early development of the nervous system in the locust larva.     

The Larvae of the Mesozoic family Aeschnidiidae and their Phylogenetic Implications (Insecta, Odonata, Anisoptera)

Four giant dragonfly larvae are described from the Lower Cretaceous of China. Owing to the preservation of wing tracheal venation on the larval wing sheaths, they can be identified as the first undoubted larvae of the extinct Mesozoic family Aeschnidiidae. They are ultimate or penultimate male and female specimens, and a younger larva. The female larva has a very long ovipositor sheath. These larvae have an anisopteran anal pyramid and a very particular spoon-shaped labial mask, with a very narrow prementum and large palps with numerous teeth, suggesting possible affinities of the Aeschnidiidae with the Anisoptera Cavilabiata. The positions of other larvae formally attributed to the Aeschnidiidae are discussed, i.e. Nothomacromia sensibilis (Carle and Wighton, 1990), Sona nectes Pritykina, 1986, and the alleged larvae of Hemeroscopus baissicus Pritykina, 1977. They differ greatly from the true Chinese larval Aeschnidiidae, in the labial mask and female ovipositor, even if they show some similarities in the anal pyramid.     

Allometric growth and larval development in Pacific red snapper Lutjanus peru under culture conditions

Allometric growth is a common feature during fish larval development. It has been proposed as a growth strategy to prioritize the development of body segments related to primordial functions like feeding and swimming to increase the probability of survival during this critical period. In the present study we evaluated the allometric growth patterns of body segments associated to swimming and feeding during the larval stages of Pacific red snapper Lutjanus peru. The larvae were kept under intensive culture conditions and sampled every day from hatching until day 33 after hatching. Each larva was classified according to its developmental stage into yolk-sac larva, preflexion larva, flexion larva or postflexion larva, measured and the allometric growth coefficient of different body segments was evaluated using the potential model. Based on the results we can infer the presence of different ontogenetic priorities during the first developmental stages associated with vital functions like swimming during the yolk-sac stage [total length (TL) interval = 2.27–3.005 mm] and feeding during the preflexion stage (TL interval = 3.007–5.60 mm) by promoting the accelerated growth of tail (post anal) and head, respectively. In the flexion stage (TL interval = 5.61–7.62 mm) a change in growth coefficients of most body segments compared to the previous stage was detected, suggesting a shift in growth priorities. Finally, in the postflexion stage (TL interval = 7.60–15.48 mm) a clear tendency to isometry in most body segments was observed, suggesting that growth priorities have been fulfilled and the larvae will initiate with the transformation into a juvenile. These results provide a framework of the larval growth of L. peru in culture conditions which can be useful for comparative studies with other species or in aquaculture to evaluate the changes in larval growth due to new conditions or feeding protocols.     

Larval ontogeny and morphology of the fire-tailed gudgeon, Hypseleotris galii (Eleotridae)

The larval ontogeny of Hypseleotris galii is described and illustrated. 'Premature' yolk sac larvae hatch with unpigmented eyes and no mouth. 'Late' yolk sac larvae hatch with pigmented eyes and a functional mouth. Hatching glands are distributed on the head and ventral surface of the body. The yolk is absorbed and the larvae begin feeding 6 days after hatching. Larval development is completed 74 days after hatching. Hypseleotris galii larvae have six pairs of naked neuromasts: two pairs on the head and four pairs on the body. The significance of these results to developmental strategies in Hypseleotris species is discussed.     

A description of the first instar larva of Promecognathus Chaudoir (Coleoptera: Carabidae)

The first instar larva of Promecognathus laevissimus (Dejean) is described, representing the first species of Promecognathus known in the larval stage. The larva is autapomorphic in having: (1) additional setae, often in great number, on many sclerites of the body, (2) a transverse, not bulbous, sensory area located ventrally and laterally at the apex of antennomere III, and (3) the marginal area of the mesonotum, metanotum and abdominal tergites I-VI more expanded than usual in carabid larvae. No evidence was found from the larval morphology of P.laevissimus to indicate the sister group of the Promecognathini.     

Egg size and larval development in Central Amazonian fish

The relationship between larval development and egg size was studied in 14 species of Central Amazonian fish (seven characiforms, five cichlids and two siluriforms). Egg size was measured as yolk dry weight at activation (egg minus chorion). Larval development was measured as larva] dry weight and age (h from activation) at the developmental stages. Egg size explained most of the variability of larval body weight and total larval weight at hatching, pectoral bud formation, eye pigmentation, jaw formation, swimbladder inflation, onset of swimming, first feeding and maximum weight attained with exclusively endogenous feeding. Larval ages at these developmental stages were poorly related to egg size. Other variables, such as the weight-specific yolk caloric content of the eggs (cal mg⁻¹), spawning site (river or lake) and phyletic relationships had no effect on the remaining variance. These results suggest that the developmental stages considered were conservative among the species examined and that a sequence of stages occurs in the larval development of Amazonian larval fish. The resistance of the larvae to starvation was not related to egg size.     

On the Larval Protonephridial System of Gyrocotyle and the Evolution of Cercomeromorphae (Platyhelminthes)

Eggs of Gyrocotyle urna specimens were hatched. Certain results from the hatching work are given. The protonephridial system of the larvae/lycophores was investigated. The system was found to be bilaterally symmetrical with two nephridiopores in the anterior body-half. The system is very similar to the posterior protonephridial system in the oncomiracidium (the monogenoidean larva). Unlike the oncomiracidium the Gyrocotyle lycophore has no anterior system. The hooks of amphilinidean and gyrocotylidean lycophores were found to be of the same basic type as those of other cercomero-morphaean larvae. A preliminary investigation of the hook ontogeny of Amphilina foliacea was made: all ten hooks appear to begin developing at the same time, the six ordinary hooks early assumed a similar shape and arrangement to those in the oncosphaera, the four aberrant hooks seem to be less aberrant in their earlier developmental stages. On a basis of the number of hooks and other facts relating to the larvae, cercomero-morphaean evolution at the larval level is claimed. Because there are no traces of a mouth, a pharynx and an intestine in the ontogeny of Gyrocotyle , the lack of these body parts in the lycophore is assumed to be a primitive condition. It is claimed that the monogenoidean protonephridial system originated from a system of the Gyrocotyle lycophore type and that the mouth, pharynx and intestine are secondarily evolved in the monogenoideans. It is assumed that mouth-, pharynx- and intestine-less creatures with an ingestive body-covering gave rise to the digenean and the cercomeromorphaean evolutionary lines. On a basis of the ontogeny and the life cycles in the different cercomeromorphaean groups it is claimed that the adult monogenoideans never reached a certain evolutionary level which is repeated in the ontogeny of the ces-todes, the amphilinideans and the gyrocotylideans.     

长吻(鱼危)幼鱼发育的研究

长吻(鱼危)的幼鱼发育共分为仔鱼前期、仔鱼期和稚鱼期三个阶段。本文记述的是幼鱼发育各阶段外部形态的变化和内部器官的建成以及不同时期出现的集群、摄食、避光等生物学特性。对提高鱼苗成活率,培育出优质健壮的苗种有指导意义。       

TOTAL CELL NUMBER AND NUMBER OF THE PRIMARY MESENCHYME CELLS IN WHOLE, 1/2 AND 1/4 LARVAE OF CLYPEASTER JAPONICUS*

Total cell number and number of the primary mesenchyme cells of 1/2 and 1/4 larvae were counted at several developmental stages after hatching in comparison with those of a whole larva, using Clypeaster japonicus as material. To obtain partial larvae, blastomeres were isolated at the 2- or 4-cell stage in Ca-free sea water and cultured in natural sea water at around 23°C. Isolated blastomeres cleaved as in situ, namely, as a part of an embryo. Although each partial embryo tended to spread into a plate, it acquired spherical shape prior to hatching of control whole embryo and developed normally in terms of both developmental rate and morphogenesis. Total cell number of a whole larva was about 620 just after hatching and increased almost linearly until i t reached 1850 at the pluteus stage. A half and quarter larvae contained roughly 1/2 and 1/4, respectively, of the number of cells of whole larva through all stages counted. Numbers of the primary mesenchyme cells in the partial larvae, however, tended to be slightly larger than a half or a fourth of that in whole larva. In whole larva, 35, 50, 56 and 58 was counted at the mesenchyme blastula, early gastrula, late gastrula and pluteus stage, respectively.     

The calliphorid larvae parasitic on birds in Japan (Diptera: Calliphoridae)

The immature stages of Protocalliphora maruyamensis Kano et Shinonaga are newly described and the third instar larva of P. azurea (Fallén) is redescribed from specimens collected in Japan. The larval morphology of Protocalliphora is discussed. A key to the third instar larvae of Japanese bird-parasitic blowflies is given.     

The larvae of the burrowing mayfly genus Tortopus (Ephemeroptera: Polymitarcyidae)

The larval stage of Tortopus is redescribed based on three species: T. puella from North America, the only species of the genus previously known from larva, and the larvae of T. obscuripennis and T. sarae from South America described here. Generic characters of the larva include: relatively large finger-like gill near base of maxilla, inner margin of mandibular tusks with a subdistal tubercle, straight or weakly convex frontal ridge present between antennae, reduced unilamellated gill on abdominal segment I. Additionally the male imagines of both Neotropical species are described for the first time, and T. obscuripennis is recorded from Bolivia. Diagnoses, SEM photographs, and illustrations are given for the new stages described and for the identification of the three Tortopus species known as larvae.     

Hemps, a novel EGF-like protein, plays a central role in ascidian metamorphosis

All chordates share several characteristic features including a dorsal hollow neural tube, a notochord, a pharynx and an endostyle. Unlike other chordate taxa, ascidians have a biphasic life-history with two distinct body plans. During metamorphosis, the larval nerve cord and notochord degenerate and the pharyngeal gill slits and endostyle form. While ascidians, like other marine invertebrates, metamorphose in response to specific environmental cues, it remains unclear how these cues trigger metamorphosis. We have identified a novel gene (Hemps) which encodes a protein with a putative secretion signal sequence and four epidermal growth factor (EGF)-like repeats which is a key regulator of metamorphosis in the ascidian Herdmania curvata. Expression of Hemps increases markedly when the swimming tadpole larva becomes competent to undergo metamorphosis and then during the first 24 hours of metamorphosis. The Hemps protein is localised to the larval papillae and anterior epidermis of the larva in the region known to be required for metamorphosis. When the larva contacts an inductive cue the protein is released, spreading posteriorly and into the tunic as metamorphosis progresses. Metamorphosis is blocked by incubating larvae in anti-Hemps antibodies prior to the addition of the cue. Addition of recombinant Hemps protein to competent larvae induces metamorphosis in a concentration-dependent manner. A subgroup of genes are specifically induced during this process. These results demonstrate that the Hemps protein is a key regulator of ascidian metamorphosis and is distinct from previously described inducers of this process in terrestrial arthropods and aquatic vertebrates.     

SEM studies on the early larval development of Triops cancriformis (Bosc)(Crustacea: Branchiopoda, Notostraca)

We investigated early larval development in the notostracan Triops cancriformis (Bosc, 1801–1802) raised from dried cysts under laboratory conditions. We document the five earliest stages using scanning electron microscopy. The stage I larva is a typical nauplius, lecithotropic and without trunk limbs. The stage II larva is feeding and has trunk limb precursors and a larger carapace. Stage III larvae have larger trunk limbs and a more adult shape. Stage IV larvae have well developed trunk limbs, and stage V larvae show atrophy of the antennae. We describe the ontogeny of selected features such as trunk limbs and carapace, discuss ontogeny and homologization of head appendages, follow the development of the feeding mechanism, and discuss trunk limb ontogeny.