Larval Structures Research Articles

Differentiation of the Swimbladder Structure in Larvae of the Red Seabream Pagrus major

Differentiation of the Swimbladder Structure in Larvae of the Red Seabream Pagrus major

Composition and daytime vertical distribution of the ichthyoplankton assemblage in the Central Cantabrian Sea shelf, during summer: An Eulerian study

During summer, wind driven coastal upwelling dominates in the Central Cantabrian Sea (southern Bay of Biscay). Nevertheless, atmospheric forcing is highly variable and wind pulses may cause noticeable and fast hydrographic responses in the shelf region. In this paper, the composition and vertical distribution of the summer ichthyoplankton assemblage during the daytime at a fixed station, located on the Central Cantabrian Sea shelf, are documented. Also, the impact of a short-time scale hydrographic event on the abundance and structure of the larval fish assemblage is examined. Significant small-scale temporal hydrographic variability was observed. Currents showed changes in speed and direction and significant changes in thermocline depth were also observed. A total of 34 taxa of fish larvae were identified. Engraulis encrasicolus eggs and larvae of the shelf-dwelling species Trachurus trachurus, Capros aper and E. encrasicolus dominated the ichthyoplankton assemblage. The distribution of E. encrasicolus eggs and fish larvae was vertically structured. E. encrasicolus egg concentration increased exponentially towards the surface. Fish larvae showed a subsurface peak of concentration and their vertical distribution was not conditioned by thermocline depths. The short term hydrographic event did not affect the vertical distribution of fish larvae but it accounted for significant temporal changes in larval fish assemblage structure and abundance. Results suggest that temperature and light intensity are important factors in the vertical distribution of fish larvae. They also indicate that the temporal monitoring of the larval fish assemblage in this region requires multiple sampling sites.

Where are larvae of the vermetid gastropod Dendropoma maximum on the continuum of larval nutritional strategies?

This study evaluated whether larvae of the Indo-Pacific vermetid gastropod Dendropoma maximum are obligate planktotrophs, or whether they exhibit an intermediate feeding strategy. Experiments were conducted in Moorea, French Polynesia (14950 0 W, 1730 0 S), Sep- Oct 2009, to examine D. maximum larval growth and metamorphic responses to different diets and amounts of food. Dendropoma maximum larvae required particulate food to undergo metamorphosis, but were able to survive and grow in the absence of food for up to 20 days. Larvae in Low and Unfed food treatments exhibited phenotypic plasticity by growing a larger velum (the larval feeding structure) compared with those in high food. Unfed D. maximum larvae had a slower initial growth rate; however, by 11-day post-hatch fed and unfed larvae had converged on the same mean shell height (553 lm), which was only 10% larger than the initial size at hatching. Therefore, although the nutritional strategy of D. maximum larvae is best described as obligate planktotrophy, it appears to approach an intermediate feeding strategy.

A new Cocos-eating moth of Acria Stephens, 1834 (Lepidoptera, Peleopodidae) from China, with descriptions of its adult, larva and pupa

A species of Acria Stephens, 1834 is reported as new to science, namely Acria cocophaga sp. nov. Descriptions and illustrations of adults, genital, larval and pupal structures are all provided. The types of the species are deposited at the Institute of Zoology, Chinese Academy of Sciences (IZCAS).

Loss of Sensory Elements in the Apical Sensory Organ During Metamorphosis in the Nudibranch Phestilla sibogae

Larvae of the nudibranch Phestilla sibogae are induced to metamorphose by a water-borne chemical cue released by the adult nudibranch's prey, the coral Porites compressa. In competent larvae, the apical sensory organ (ASO) includes five serotonergic parampullary neurons; five ampullary neurons, the ampullae of which are filled with sensory cilia; and a basal neuropil. After sensing the coral cue, the ASO undergoes radical morphological changes: a deterioration of sensory elements in the ASO and serotonergic axons originating from them to innervate the velum. Three hours after metamorphic induction, the velar lobes are lost, the serotonergic axons begin to break apart, the five parampullary neurons begin to degenerate, and the five ampullary neurons retract away from the epidermal surface. The extent of deterioration evident by this time suggests that the parampullary and ampullary components of the ASO are no longer functional. By 10 h after metamorphic induction, labeling of the ciliary bundles in the ampullary neurons has disappeared, and it is likely that these cells have degenerated. The results presented here provide evidence that the sensory neurons of the ASO and probably the entire organ are solely larval structures that do not persist into the adult sensory-nervous system in P. sibogae.

Structure and expression of conserved Wnt pathway components in the demosponge Amphimedon queenslandica

Wnt-signalling plays a critical role in animal development, and its misregulation results in serious human diseases, including cancer. While the Wnt pathway is well studied in eumetazoan models, little is known about the evolutionary origin of its components and their functions. Here, we have identified key machinery of the Wnt-β-catenin (canonical)-signalling pathway that is encoded in the Amphimedon queenslandica (Demospongiae; Porifera) genome, namely Wnt, Fzd, SFRP, Lrp5/6, Dvl, Axin, APC, GSK3, β-catenin, Tcf, and Groucho. Most of these genes are not detected in the choanoflagellate and other nonmetazoan eukaryotic genomes. In contrast, orthologues of some of key components of bilaterian Wnt-planar cell polarity and Wnt/Ca(2+) are absent from the Amphimedon genome, suggesting these pathways evolved after demosponge and eumetazoan lineages diverged. Sequence analysis of the identified proteins of the Wnt-β-catenin pathway has revealed the presence of most of the conserved motifs and domains responsible for protein-protein and protein-DNA interactions in vertebrates and insects. However, several protein-protein interaction domains appear to be absent from the Amphimedon Axin and APC proteins. These are also missing from their orthologues in the cnidarian Nematostella vectensis, suggesting that they are bilaterian novelties. All of the analyzed Wnt pathway genes are expressed in specific patterns during Amphimedon embryogenesis. Most are expressed in especially striking and highly dynamic patterns during formation of a simple organ-like larval structure, the pigment ring. Overall, our results indicate that the Wnt-β-catenin pathway was used in embryonic patterning in the last common ancestor of living metazoans. Subsequently, gene duplications and a possible increase in complexity of protein interactions have resulted in the precisely regulated Wnt pathway observed in extant bilaterian animals.

Neuromuscular system of the larva of Fredericella sultana (Bryozoa: Phylactolaemata)

Phylactolaemate Bryozoa exhibit sexually produced larval stages, which bear one or more fully developed polypides. Following settlement, the polypides evert and start feeding immediately. This is in sharp contrast to the so-called “catastrophic” metamorphosis of gymnolaemate and stenolaemate larvae, during which almost all larval tissues are resorbed and adult tissues formed de novo. Because of these striking differences, homology relationships between larval structures as well as the larvae themselves have remained uncertain. The musculature of Fredericella sultana larvae mainly consists of adult elements, which have functions in the polypide and persist through metamorphosis. Two independent serotonergic nervous systems are found: one in the polypide and one in the apical hemisphere of the ciliated body wall, which degrades during metamorphosis. The latter system includes a basiepithelial nerve net and a concentration of serotonergic cells in the region of the apical plate. FMRFamidergic nerves are found in the entire ciliated larval surface, but not in the polypide. The separate origin of larval and adult serotonergic nervous systems, which remain unconnected is most likely ancestral and apomorphic for Bryozoa and argues for the homology of bryozoan larval forms. The pattern of serotonergic cells in the phylactolaemate apical plate does not show similarities to the apical organ in gymnolaemate bryozoans. Instead, these cells might be homologous to serotonergic intercoronal cells present in gymnolaemate larvae. This, along with the occurrence of gland cells in the apical plate supports the view that the apical pole of phylactolaemate larvae corresponds to oral pole of gymnolaemate larve.

Serotonin immunoreactivity in the nervous system of the Pandora larva, the Prometheus larva, and the dwarf male of Symbion americanus (Cycliophora)

Cycliophora is a recently described phylum of enigmatic metazoans with a very complex life cycle that includes several sexual and asexual stages. Symbion pandora and Symbion americanus are the only two cycliophoran species hitherto described, of which morphological and genetic knowledge is still deficient to clarify the phylogenetic position of the phylum. Aiming to increase the database on the cycliophoran neural architecture, we investigated serotonin immunoreactivity in the free swimming Pandora larva, the Prometheus larva, and the adult dwarf male of S. americanus. In the larval forms, serotonin is mainly expressed in a ring-shaped pattern at the periphery of the antero-dorsal cerebral ganglion. Additionally, several serotonergic perikarya emerge from both sides of the cerebral ganglion. Thin neurites project anteriorly from the cerebral ganglion, while a pair of ventral longitudinal neurites emerges laterally and runs along the anterior-posterior body axis. Posteriorly, the ventral neurites fuse and extend as a posterior projection. In the dwarf male, serotonin is found mainly in the commissural neuropil of the large anterior cerebral ganglion. In addition, serotonin immunoreactivity is present in the most anterior region of the ventral neurites. Comparative analysis of spiralian nervous systems demonstrates that the neuroanatomy of the cycliophoran larval stages resembles much more the situation of adult rather than larval spiralians, which may be explained by secondary loss of larval structures and heterochronic shift of adult components into the nervous system of the Pandora and the Prometheus larva, respectively .

Does larval supply explain the low proliferation of the invasive gastropod Crepidula fornicata in a tidal estuary?

Human-mediated transport and aquaculture have promoted the establishment of non-indigenous species in many estuaries around the world over the last century. This phenomenon has been demonstrated as a major cause of biodiversity alterations, which has prompted scientists to provide explanations for the success or failure of biological invasions. Crepidula fornicata is a gastropod native from the East coast of North America which has successfully invaded many European bays and estuaries since the 19th century, with some noticeable exceptions. Its spread over Europe has been explained by a combination of human-mediated transport and natural dispersal through its long-lived planktonic larva. We here investigated whether larval supply may explain the failure in the proliferation of this species within a particular bay, the Bay of Morlaix (France). Patterns of larval distribution and larval size structure were analysed over ten sites sampled three times (20 July, 4 August and 21 August 2006), regarding characteristics of the adult population and environmental features. Our results evidenced a strong spatial structure in both larval abundance and size at the bay scale, even if larval abundances were low. In this scheme, the location of spawning adults played a critical role, with high numbers of early larvae above the main spawning location. The larval size structure further showed that settlement-stage larvae were rare, which suggested that released larvae might have been exported out of the bay. The use of an analytical model aimed to study the effect of tidal currents on the potential for larval exportation confirmed that larval retention within the bay might be low. The limitation in larval supply resulting from the interactions between spawning location and local hydrodynamics may thus impede the proliferation of this species which is well established for more than 50 years. This study provided an example of factors which may explain the failure of the transition between two major steps of biological invasions, i.e. sustainable establishment and proliferation.

External morphology of Cotesia flavipes (Hymenoptera: Braconidae) during larval development

Cotesia flavipes (Cameron, 1891) (Hymenoptera) is a gregarious endoparasitoid used in applied biological control against Diatraea saccharalis (Fabricius, 1794) (Lepidoptera). In this study, we characterize the larval external morphology and the number of instars of C. flavipes. Parasitized larvae of D. saccharalis were sampled from the 1st to the 10th day after parasitism and dissected in an anticoagulant buffer for collection of C. flavipes immatures. Immatures were processed for scanning electron microscopy. Larvae of C. flavipes were prepared in NaOH solution and slide mounted to allow for mandible size measurements. Analysis of measurements of the parasitoid larval mandible size indicated that C. flavipes has three instars. Newly hatched larvae are caudate-mandibulate, assuming a hymenopteriform shape later in their development. The anal vesicle began to expand in the first instar and, once expanded, remained unchanged up to the beginning of the third instar. At the third instar, the anal vesicle decreased in volume. Herein we report the development and possible functions of the larval external structures modified during the development of C. flavipes, as for example their role in aiding newly-eclosed larvae to avoid the host immune response and to move within the host. To summarize the morphological changes during parasitoid growth, we should mention that the modifications in the anal vesicle were correlated with the feeding activity, and the maintenance of the anal vesicle indicates that this structure remained functional, probably playing a role in nutrient absorption and host regulation. On the other hand, the mandibles of early stage larvae are probably used to assist the parasitoid larvae during eclosion.

Dose-dependent effects of chlorpyriphos, an organophosphate pesticide, on metamorphosis of the sea urchin, Paracentrotus lividus

The effect of exposures to the insecticide chlorpyrifos on the larval stages of Paracentrotus lividus (Echinodermata, Euechinoidea) up to metamorphosis was investigated with the aim to identify novel risk biomarkers and a new promising model for toxicity tests. The planktonic sea urchin larvae have the ability to undergo a variable exploratory period, up to the choice of a suitable substrate for adult benthonic life. The juvenile bud (called rudiment) is built inside the larval body that, on environmental cues represented by a variety of signal molecules, is reabsorbed by apoptosis and releases the juvenile on the substrate. In this dialogue between larvae and environment, contaminants interfere with the signals reception, and may alter in dose-dependent way the correct regulation of environment-larva-rudiment interaction. Such interaction is shown by larval plasticity, i.e. the ability of the larva to change body proportions according to the environmental conditions. When exposed to low doses of chlorpyriphos (10(-7) to 10(-10) M) since 2-days after fertilization, the larvae showed altered size and shape, but all reached the metamorphosis at the same time as controls, and in the same percentage. Exposures to high concentrations such as 10(-4) to 10(-6) M since 2-days after fertilization did not allow larval growth and differentiation. Exposures at later stages caused reabsorption of larval structures within a few hours and precocious release of the immature rudiments, followed by death of the juveniles. Although the mechanism of chlorpyriphos toxicity in sea urchin larvae is still rather unclear, the measurable stress biomarkers can constitute the basis for new toxicity tests.

Relative importance of water column vs zooplankton variables in the determination of late-stage larval fish assemblage structure in coastal waters of a coral reef lagoon

SUMMARY: The relationship between fish larvae and their zooplanktonic prey has not been fully explored for late-stage larvae of coral-reef fish in lagoonal environments. However, compared to most temperate taxa, these larvae are characterized by strong sensory and swimming abilities, which may influence their feeding behaviour in the water column. The present study aims to determine the relative importance of the water column and zooplankton variables for the structure of pre-settlement larval fish assemblages within a single season in three bays of the coral reef lagoon of New Caledonia, southwest Pacific. The structure of larval assemblages was found to be explained better by water column variables in two out of the three bays examined. Zooplankton variables only played a role in one bay out of the three, probably due to the lower variability in the water column variables. Moreover, the relationship between total larval fish abundance and zooplankton density was not significant in any of the three bays. These results suggest that the relationship between late-stage coral-reef fish larvae and their prey: 1) is difficult to detect at small spatial and temporal scales, 2) is probably complex and non-linear, 3) depends on environmental conditions, and 4) probably varies between fish taxa.

Ambulatory Use of Ventro-Lateral Abdominal Ampullae by Larvae of Labidomera clivicollis(Kirby) (Coleoptera: Chrysomelidae: Chrysomelinae)

Abstract Ampullae appear to be common in the larvae of some chrysomelid subfamilies. We describe and discuss the occurrence and use of these structures in larvae of Labidomera clivicollis (Kirby), on its host plant Asclepias verticillata L. (Asclepiadaceae) under field and lab conditions. Through film footage, we reveal that ventral ampullae are apparent on all ten segments of the larval abdomen; however, only those associated with segments AVIII–AX were actually used in ambulation by anchoring to the host plant. These ampullae always function with the true legs during movement. Our study unveils ambiguities in homology and terminology of abdominal ambulatory structures that are relevant to discussions of chrysomelid characters and phylogeny.

Larval Development With Transitory Epidermis inParanemertes peregrinaand Other Hoplonemerteans

We describe development of the hoplonemertean Paranemertes peregrina from fertilization to juvenile, using light, confocal, and electron microscopy. We discovered that the uniformly ciliated lecithotrophic larva of this species has a transitory epidermis, which is gradually replaced by the definitive epidermis during the course of planktonic development. The approximately 90 large multiciliated cleavage-arrested cells of the transitory larval epidermis become separated from each other by intercalating cells of the definitive epidermis, then gradually diminish in size and disappear more or less simultaneously. Rudiments of all major adult structures-the gut, proboscis, cerebral ganglia, lateral nerve cords, and cerebral organs-are already present in 4-day-old larvae. Replacement of the epidermis is the only overt metamorphic transformation of larval tissue; larval structures otherwise prefigure the juvenile body, which is complete in about 10 days at 7-10 degrees C. Our findings on development of digestive system, nervous system, and proboscis differ in several ways from previous descriptions of hoplonemertean development. We report development with transitory epidermis in two other species, review evidence from the literature, and suggest that this developmental type is the rule for hoplonemerteans. The hoplonemertean planuliform larva is fundamentally different both from the pilidium larva of the sister group to the Hoplonemertea, the Pilidiophora, and from the hidden trochophore of palaeonemerteans. We discuss the possible function and homology of the larval epidermis in development of other nemerteans and spiralians in general.

Algal Symbionts in the Larval Tunic Lamellae of the Colonial Ascidian Lissoclinum timorense (Ascidiacea, Didemnidae)

Lissoclinum timorense is a colonial ascidian that harbors the prokaryotic alga Prochloron . The algal photosymbionts adhere to the lamellae of the tunic on the posterior half of the trunk of larvae, which aggregate in the common cloacal cavity of the mother colony. Bead-adhesion tests demonstrated that the lamellae are adhesive, whereas the anterior half of the larval trunk is not. The anterior half is covered with a thin layer of outer tunic, which probably prevents Prochloron cells from attaching and interfering with sensory receptors and adhesive organs. The larval structures and the mode of algal transmission between generations are very similar to those of the Prochloron -harboring ascidian Didemnum molle . Molecular phylogenetic analyses have suggested that photosymbiosis was independently established in each genus, and thus the apparent similarity in the larvae probably resulted from convergence. The distribution pattern of photosymbionts is probably more determinative of algal transmission than phylogenetic constraints.

Loss and gain of the juvenile rudiment and metamorphic competence during starvation and feeding of bryozoan larvae

In many animals, larval structures and juvenile rudiments develop independently. One advantage of this independence is that juvenile rudiments can be expended as a nutrient reserve or for energy conservation. When bryozoan cyphonautes larvae were starved, structures required for settlement and metamorphosis shrank. When the larvae were again fed, these structures grew back. Starvation reduced the size of both the internal sac, a rudiment of postlarval juvenile structures, and the pyriform organ, which functions in sensing and crawling on the substratum at settlement. In contrast, starvation affected neither the size of the larval shell nor the lengths of the ciliary bands used in swimming and feeding. Starved larvae that had reduced the pyriform organ and internal sac did not metamorphose in response to stimuli from a laminarian alga. The laminarian alga did stimulate metamorphosis of the same larvae after renewed feeding, when the larvae had regrown these structures. Thus starved larvae expended body parts needed for settlement and metamorphosis when food was scarce while retaining structures for feeding, swimming, and defense. Starved larvae thereby retained the capacity to regrow structures needed for settlement and metamorphosis when they again encountered food. Advantages from expendable juvenile rudiments may enhance selection for their being developmentally distinct from structures for larval swimming and feeding.

Immature Stages of Caria plutargus (Lepidoptera: Riodinidae), with Discussion on the Behavioral and Morphological Defensive Traits in Nonmyrmecophilous Riodinid Butterflies

Aspects of the natural history and early stage morphology of the nonmyrmecophilous butterfly Caria plutargus (F.) (Lepidoptera: Riodinidae) are described. Immature stages were observed through scanning electron microscopy, emphasizing larval structures that may be related to myrmecophily or not. The larvae have several types of setae (balloon, echinoid, dendritic, plumose) and perforated cupola organs. The presence of balloon setae in C. plutargus is the first record for Riodinini. These structures have been described for some Riodinidae tribes, such as Nymphidiini and Helicopini, and also for some taxa in the incertae sedis section. The literature has proposed that balloon setae play a role in the symbiosis between larvae and ants in myrmecophilous riodinids. However, the discovery of balloon setae in nonmyrmecophilous riodinids spurs a new debate concerning the function and evolution of these specialized setae (Ann. Entomol. Soc. Am. 97: 310–321, 2004). The morphological and behavioral traits here described are discussed in the context of defense against predators.

Immature Stages of <I>Caria plutargus</I> (Lepidoptera: Riodinidae), with Discussion on the Behavioral and Morphological Defensive Traits in Nonmyrmecophilous Riodinid Butterflies

Aspects of the natural history and early stage morphology of the nonmyrmecophilous butterfly Caria plutargus (F.) (Lepidoptera: Riodinidae) are described. Immature stages were observed through scanning electron microscopy, emphasizing larval structures that may be related to myrmecophily or not. The larvae have several types of setae (balloon, echinoid, dendritic, plumose) and perforated cupola organs. The presence of balloon setae in C. plutargus is the first record for Riodinini. These structures have been described for some Riodinidae tribes, such as Nymphidiini and Helicopini, and also for some taxa in the incertae sedis section. The literature has proposed that balloon setae play a role in the symbiosis between larvae and ants in myrmecophilous riodinids. However, the discovery of balloon setae in nonmyrmecophilous riodinids spurs a new debate concerning the function and evolution of these specialized setae (Ann. Entomol. Soc. Am. 97: 310-321, 2004). The morphological and behavioral traits here described are discussed in the context of defense against predators.

Larval morphology of the brooding clam Lasaea adansonii (Gmelin, 1791) (Bivalvia, Heterodonta, Galeommatoidea)

The strongly modified mode of development of the small and brooding galeommatoid bivalve Lasaea adansonii (Gmelin, 1791) [syn. Lasaea rubra (Montagu, 1803)] has been studied by means of transmission and scanning electron microscopy and by fluorescent staining of the muscular system and of two neurotracers, FMRFamide and serotonin. In addition, two developmental stages were visualized using computer-aided 3D-reconstruction. All larval stages of L. adansonii lack ciliary rings. The apical organ appears invaginated: the base of the duct contacts the cerebral ganglia and opens on the preoral region. Larval protonephridia are lacking. The adult kidneys develop independently of the pericardial cavity and contain a protonephridial part that enables excretory function until the pericardium is formed. The larval muscular system is composed of smooth muscle fibers; striated fibers are lacking. Posteriorly and immediately below the ligament, a paired cell of unknown function is present that contains serotonin and FMRFamide. In summary, L. adansonii exhibits the direct mode of development. Only few truly larval structures (e.g., the modified apical organ) are elaborated.

Larval cells become imaginal cells under the control of homothorax prior to metamorphosis in the Drosophila tracheal system

In Drosophila melanogaster, one of the most derived species among holometabolous insects, undifferentiated imaginal cells that are set-aside during larval development are thought to proliferate and replace terminally differentiated larval cells to constitute adult structures. Essentially all tissues that undergo extensive proliferation and drastic morphological changes during metamorphosis are thought to derive from these imaginal cells and not from differentiated larval cells. The results of studies on metamorphosis of the Drosophila tracheal system suggested that large larval tracheal cells that are thought to be terminally differentiated may be eliminated via apoptosis and rapidly replaced by small imaginal cells that go on to form the adult tracheal system. However, the origin of the small imaginal tracheal cells has not been clear. Here, we show that large larval cells in tracheal metamere 2 (Tr2) divide and produce small imaginal cells prior to metamorphosis. In the absence of homothorax gene activity, larval cells in Tr2 become non-proliferative and small imaginal cells are not produced, indicating that homothorax is necessary for proliferation of Tr2 larval cells. These unexpected results suggest that larval cells can become imaginal cells and directly contribute to the adult tissue in the Drosophila tracheal system. During metamorphosis of less derived species of holometabolous insects, adult structures are known to be formed via cells constituting larval structures. Thus, the Drosophila tracheal system may utilize ancestral mode of metamorphosis.