Functional morphogenesis from embryos to adults: Late development shapes trophic niche in coral reef damselfishes

The damselfishes are one of the dominant coral reef fish lineages. Their ecological diversification has involved repeated transitions between pelagic feeding using fast bites and benthic feeding using forceful bites. A highly‐integrative approach that combined gene expression assays, shape analyses, and high‐speed video analyses was used to examine the development of trophic morphology in embryonic, larval, juvenile, and adult damselfishes. The anatomical characters that distinguish pelagic‐feeding and benthic‐feeding species do not appear until after larval development. Neither patterns of embryonic jaw morphogenesis, larval skull shapes nor larval bite mechanics significantly distinguished damselfishes from different adult trophic guilds. Analyses of skull shape and feeding performance identified two important transitions in the trophic development of a single species (the orange clownfish; Amphiprion percula): (a) a pronounced transformation in feeding mechanics during metamorphosis; and (b) more protracted cranial remodeling over the course of juvenile development. The results of this study indicate that changes in postlarval morphogenesis have played an important role in damselfish evolution. This is likely to be true for other fish lineages, particularly if they consist of marine species, the majority of which have planktonic larvae with different functional requirements for feeding in comparison to their adult forms.     

Biosynthesis and metabolism of sulfated glycosaminoglycans during Drosophila melanogaster development

We developed a simple methodology for labeling sulfated glycosaminoglycans (GAGs) in adult Drosophila melanogaster and studied some aspects of the biosynthesis and metabolism of these polymers during development. Adult D. melanogaster flies were fed with Na(2)(35)SO(4) for 72 h. During this period, (35)S-sulfate was incorporated into males and females and used to synthesize (35)S-sulfate-heparan sulfate (HS) and (35)S-sulfate-chondroitin sulfate (CS). The incorporation of (35)S-sulfate into HS was higher when compared to CS. In a pulse-chase experiment, we observed that (35)S-sulfate incorporated into adult female was recovered in embryos and used for the synthesis of new (35)S-sulfate-GAGs after 2 h of embryonic development. The synthesis of CS was higher than that of HS, indicating a change in the metabolism of these glycans from adult to embryonic and larval stages. Analysis of the CS in embryonic and larval tissues revealed the occurrence of nonsulfated and 4-sulfated disaccharide units in embryos, L1 and L2. In L3, in addition to these disaccharides, we also detected significant amount of 6-sulfated units that are reported here for the first time. Immunohistochemical analysis indicated that HS and CS were present in nonequivalent structures in adult and larval stages of the fly. Overall, these results indicate that (35)S-sulfate-precursors are transferred from adult to embryonic and larval tissues and used to assemble different morphological structures during development.     

Asymmetric larval head and mandibles of Hydrophilus acuminatus (Insecta: Coleoptera,Hydrophilidae): Fine structure and embryonic development

The larvae of a water scavenger beetle, Hydrophilus acuminatus, have strongly asymmetric mandibles; the right one is long and slender, whereas the left one is short and stout. The fine structure and embryonic development of the head capsule and mandibles of this species were examined using light and scanning electron microscopy, and asymmetries in shape were detected in these structures applying an elliptic Fourier analysis. The larval mandibles are asymmetric in the following aspects: whole length, the number, structure and arrangement of retinacula (inner teeth), and size and shape of both the molar and incisor regions. The larval head is also asymmetric; the left half of the head capsule is larger than the right, and the left adductor muscle of the mandible is much thicker than the right. The origin and developmental process of asymmetric mandibles were traced in developing embryos whose developmental period is about 270 h and divided into 10 stages. Mandibular asymmetries are produced by the cumulative effects of six stepwise modifications that occur from about 36% of the total developmental time onward. The significance of these modifications was discussed with respect to the functional advantages of asymmetries and the phylogeny of members of the Hydrophilidae.     

Phenotypic plasticity and mechano‐transduction in the teleost skeleton

The proper formation, growth and maintenance of many bones depends on the mechanical loads generated by gravity and muscles. Mechanical loading by muscle forces does not only affect bone growth and maintenance in adult and juvenile vertebrates, but also affects larval and embryonic bone development. We have reviewed the current understanding of mechanotransduction in birds and mammals and compared it to teleosts. The major mechanosensing cells in the adult mammalian and avian skeleton are osteocytes. They are interconnected via cell processes and are contained within a canalicular network. Basal teleosts have osteocytes but their connectivity is questionable and the presence of a functional canalicular network is unlikely. Advanced teleosts have acellular bone and therefore lack osteocytes. Yet the skeleton of teleosts does show adaptive responses to changes in mechanical load. In these animals it is likely that osteoblasts, bone surface cells and chondrocytes act as mechanosensors. The factors expressed by osteocytes upon mechanical stimulation have been extensively investigated in vitro and in vivo in adult mammals and birds. Less is, however, known about the mechanotransduction pathway during embryonic bone development. The zebrafish presents new opportunities to analyze the mechanotransduction pathway during early (larval) bone formation due to the ex utero development and genetic analyses.     

Developmental and evolutionary implications of labial, Deformed and engrailed expression in the Drosophila head.

Prior developmental genetic analyses have shown that labial (lab) and Deformed (Dfd) are homeotic genes that function in the development of the embryonic (larval) and adult head. Using antibody probes to reveal the spatial distribution of the lab and Dfd proteins in embryonic and imaginal tissues, we have assessed the respective roles of these genes through an analysis of the correspondence of their expression patterns with their mutant phenotypes. With regard to imaginal development, lab and Dfd occupy adjacent non-overlapping expression domains in the peripodial cell layer of the eye-antennal disc, in patterns that are consistent with their adult mutant phenotypes and published fate maps. During embryogenesis, lab and Dfd exhibit limited overlapping expression in areas that are of no obvious significance to the development of larval head structures, but also in areas that may have consequences for imaginal development. The head of Drosophila and other cyclorrhaphous Dipterans is characterized by an extreme morphological difference between the larval and adult stages. Given this unique ontogenetic and phylogenetic history and the observation that homeotic transformations produced by the lab, Dfd, and proboscipedia (pb) loci are manifested only in the adult, we suggest that distinct regulatory paradigms evolved for homeotic gene function in the development of the larval versus adult head. Finally, a detailed examination of the engrailed (en) expression pattern in the embryonic head strengthens the view of insect morphologists that the clypeolabrum evolved from the fusion of paired labral appendages.     

Embryonic and larval development of the Drosophila mushroom bodies: concentric layer subdivisions and the role of fasciclin II.

Mushroom bodies (MBs) are the centers for olfactory associative learning and elementary cognitive functions in the arthropod brain. In order to understand the cellular and genetic processes that control the early development of MBs, we have performed high-resolution neuroanatomical studies of the embryonic and post-embryonic development of the Drosophila MBs. In the mid to late embryonic stages, the pioneer MB tracts extend along Fasciclin II (FAS II)-expressing cells to form the primordia for the peduncle and the medial lobe. As development proceeds, the axonal projections of the larval MBs are organized in layers surrounding a characteristic core, which harbors bundles of actin filaments. Mosaic analyses reveal sequential generation of the MB layers, in which newly produced Kenyon cells project into the core to shift to more distal layers as they undergo further differentiation. Whereas the initial extension of the embryonic MB tracts is intact, loss-of-function mutations of fas II causes abnormal formation of the larval lobes. Mosaic studies demonstrate that FAS II is intrinsically required for the formation of the coherent organization of the internal MB fascicles. Furthermore, we show that ectopic expression of FAS II in the developing MBs results in severe lobe defects, in which internal layers also are disrupted. These results uncover unexpected internal complexity of the larval MBs and demonstrate unique aspects of neural generation and axonal sorting processes during the development of the complex brain centers in the fruit fly brain.     

Laboratory spawning and development of the Bahama lancelet, Asymmetron lucayanum (cephalochordata): fertilization through feeding larvae

Here we report on spawning and development of the Bahama lancelet, Asymmetron lucayanum. Ripe adults collected in Bimini spawned the same evening when placed in the dark for 90 minutes. The developmental morphology is described from whole mounts and histological sections. A comparison between development in Asymmetron and the better known cephalochordate genus Branchiostoma reveals similarities during the early embryonic stages but deviations by the late embryonic and early larval stages. Thus, the initial positions of the mouth, first gill slit, and anus differ between the two genera. Even more strikingly, Hatschek's right and left diverticula, which arise by enterocoely at the anterior end of the pharynx in Branchiostoma, never form during Asymmetron development. In Branchiostoma, these diverticula become the rostral coelom and preoral pit. In Asymmetron, by contrast, homologs of the rostral coelom and preoral pit form by schizocoely within an anterior cell cluster of unproven (but likely endodermal) origin. Proposing evolutionary scenarios to account for developmental differences between Asymmetron and Branchiostoma is currently hampered by uncertainty over which genus is basal in the cephalochordates. A better understanding of developmental diversity within the cephalochordates will require phylogenetic analyses based on nuclear genes and the genome sequence of an Asymmetron species.     

Zygotic Lethals with Specific Maternal Effect Phenotypes in Drosophila Melanogaster. I. Loci on the X Chromosome

In order to identify all X-linked zygotic lethal loci that exhibit a specific maternal effect on embryonic development, germline clonal analyses of X-linked zygotic lethal mutations have been performed. Two strategies were employed. In Screen A germline clonal analysis of 441 mutations at 211 previously mapped X-linked loci within defined regions was performed. In Screen B germline clonal analysis of 581 larval and pupal mutations distributed throughout the entire length of the X chromosome was performed. These approaches provide an 86% level of saturation for X-linked late zygotic lethals (larval and pupal) with specific maternal effect embryonic lethal phenotypes. The maternal effect phenotypes of these mutations are described.     

The two origins of hemocytes in Drosophila

As in many other organisms, the blood of Drosophila consists of several types of hemocytes, which originate from the mesoderm. By lineage analyses of transplanted cells, we specified two separate anlagen that give rise to different populations of hemocytes: embryonic hemocytes and lymph gland hemocytes. The anlage of the embryonic hemocytes is restricted to a region within the head mesoderm between 70 and 80% egg length. In contrast to all other mesodermal cells, the cells of this anlage are already determined as hemocytes at the blastoderm stage. Unexpectedly, these hemocytes do not degenerate during late larval stages, but have the capacity to persist through metamorphosis and are still detectable in the adult fly. A second anlage, which gives rise to additional hemocytes at the onset of metamorphosis, is located within the thoracic mesoderm at 50 to 53% egg length. After transplantation within this region, clones were detected in the larval lymph glands. Labeled hemocytes are released by the lymph glands not before the late third larval instar. The anlage of these lymph gland-derived hemocytes is not determined at the blastoderm stage, as indicated by the overlap of clones with other tissues. Our analyses reveal that the hemocytes of pupae and adult flies consist of a mixture of embryonic hemocytes and lymph gland-derived hemocytes, originating from two distinct anlagen that are determined at different stages of development.     

Determinants of electrical properties in developing neurons

The regulatory mechanisms that orchestrate the developmental acquisition of electrical properties in embryonic neurons are poorly understood. Progress in this important area is dependent on the availability of preparations that allow electrophysiology to be married with genetics. The powerful genetics of the fruitfly Drosophila melanogaster has long been exploited to describe fundamental mechanisms associated with structural neuronal development (i.e. axon guidance). It has not, however, been fully employed to study the final stages of embryonic neural development and in particular the acquisition of electrical activity. This review focuses on the recent development of a Drosophila preparation that allows central neurons to be accessed by patch electrodes at both embryonic and larval stages. This preparation, which allows electrophysiology to be coupled with genetics, offers the prospect of making significant advances in our understanding of functional neuron development.     

Non-apoptotic function of apoptotic proteins in the development of Malpighian tubules of <Emphasis Type="Italic">Drosophila melanogaster</Emphasis>

Drosophila metamorphosis is characterized by the histolysis of larval structures by programmed cell death, which paves the way for the establishment of adult-specific structures under the influence of the steroid hormone ecdysone. Malpighian tubules function as an excretory system and are one of the larval structures that are not destroyed during metamorphosis and are carried over to adulthood. The pupal Malpighian tubules evade destruction in spite of expressing apoptotic proteins, Reaper, Hid, Grim, Dronc and Drice. Here we show that in the Malpighian tubules expression of apoptotic proteins commences right from embryonic development and continues throughout the larval stages. Overexpression of these proteins in the Malpighian tubules causes larval lethality resulting in malformed tubules. The number and regular organization of principal and stellate cells of Malpighian tubules is disturbed, in turn disrupting the physiological functioning of the tubules as well. Strikingly, the localization of beta-tubulin, F-actin and Disclarge (Dlg) is also disrupted. These results suggest that the apoptotic proteins could be having non-apoptotic function in the development of Malpighian tubules.     

Excretion in the mother’s body: modifications of the larval excretory system in the viviparous dermapteran, <Emphasis Type="Italic">Arixenia esau</Emphasis>

The vast majority of Dermaptera are free-living and oviparous, i.e., females lay eggs within which embryonic development occurs until the larva hatches. In contrast, in the epizoic dermapteran Arixenia esau, eggs are retained within mother’s body and the embryos and first instar larvae develop inside her reproductive system. Such a reproductive strategy poses many physiological challenges for a mother, one of which is the removal of metabolic waste generated by the developing offspring. Here, we examine how the Arixenia females cope with this challenge by analyzing features of the developing larval excretory system. Our comparative analyses of the early and late first instar larvae revealed characteristic modifications in the cellular architecture of the Malpighian tubules, indicating that these organs are functional. The results of the electron probe microanalyses suggest additionally that the larval Malpighian tubules are mainly involved in maintaining ion homeostasis. We also found that the lumen of the larval alimentary track is occluded by a cellular diaphragm at the midgut-hindgut junction and that cells of the diaphragm accumulate metabolic compounds. Such an organization of the larval gut apparently prevents fouling of the mother’s organism with the offspring metabolic waste and therefore can be regarded as an adaptation for viviparity.     

Effects of pH and aluminium on embryonic and early larval stages of Swedish brown frogs Rana arvalis, R. temporaria and R. dalmatina

The effects of pH and aluminium on embryonic and early larval stages of Swedish brown frogs Rana arvalis, R. temporaria and R. dalmatina were tested in laboratory bioassays. In all three species egg mortality and time needed for embryonic development to hatching increased when pH declined, but no significant effects were found on embryonic development when aluminium level was elevated. In R. arvalis and R. temporaria larval mortality was affected by both pH and aluminium. In both species the frequency of occurrence of larval deformities increased in acid water, and there was a synergistic effect of pH and aluminium. In R. arvalis swimming behaviour was disturbed by high levels of aluminium at pH 5. In all three species the frequency of stressed larvae increased when pH was depressed and aluminium concentration elevated, and there was a synergistic effect when both were combined. The three species differed significantly in egg mortality, time needed for embryonic development, larval mortality, larval deformities and larval stress al low pH and high aluminium levels. R. arvalis showed the highest acid tolerance and R. dalmatina was the most sensitive to low pH.     

Compensating for delayed hatching across consecutive life‐history stages in an amphibian

Environmental conditions experienced early in the ontogeny can have a strong impact on individual fitness and performance later in life. Organisms may counteract the negative effects of poor developmental conditions by developing compensatory responses in growth and development. However, previous studies on compensatory responses have largely ignored the effects that poor embryonic conditions could have during the later life stages. In this study, we examined the effects of artificially delayed development in early life over two later life history transitions by investigating the compensatory growth of larval moor frogs Rana arvalis in response to temperature variation during embryonic development, and the associated costs during the larval ′and postmetamorphic stages. Low temperature during embryonic stage lead to delayed hatching at smaller size. The groups with delayed embryonic development showed strong compensatory growth during the larval stage, and reached similar metamorphic size than the controls in a shorter time. However, the most strongly delayed group was not able to fully catch up the total development time. These compensatory responses were found in the absence of photoperiod cues indicating that the delay in embryonic development was sufficient to initiate the compensatory response in larval growth and development. No apparent costs of compensatory growth were detected in terms of morphology or locomotor performance at the juvenile stage. We found that compensatory responses can be activated as early as at the embryonic stage and extend over several consecutive life history transitions, mitigating the effects of poor conditions experienced early in development. Potential short‐term costs in natural environments and the occurrence of long‐term costs, which prevent the generalisation of a faster larval life style, are discussed.     

Evolutionary Conservation of the Larval Serotonergic Nervous System in a Direct Developing Sea Urchin

Development of the larval serotonergic nervous system is examined by indirect immunofluorescence in two congeneric species of sea urchins that exhibit divergent embryonic and larval development. Heliocidar is tuberculata undergoes indirect planktotrophic development via a pluteus larva, whereas Heliocidaris erythrogramma develops directly, passing through a brief, highly derived lecithotrophic larval stage. We have cleared the opaque embryos of H. erythrogramma and discuss internal features of its development. The serotonergic nervous system of H. tuberculata arises in the apical plate at the end of gastrulation and develops into a bilaterally symmetric ganglion lying between the anterolateral arms in the preoral hood. Putatively homologous neurons appear at the apical end of the modified larva of H. erythrogramma well after the completion of gastrulation, coincident with development of the primary podia of the adult rudiment. The neurons form a bilaterally symmetric ganglion whose orientation relative to the vestibule is conserved with respect to that found in planktotrophic larvae. This allows us to define a left and right side for this larva which lacks external points of asymmetry such as a larval mouth. The alteration in the time of nervous system development in H. erythrogramma relative to that of H. tuberculata , and other indirect developers, implicates heterochronies in cellular differentiation as an important component of the evolution of direct development.     

Continuity versus split and reconstitution: exploring the molecular developmental corollaries of insect eye primordium evolution

Holometabolous insects like Drosophila proceed through two phases of visual system development. The embryonic phase generates simple eyes of the larva. The postembryonic phase produces the adult specific compound eyes during late larval development and pupation. In primitive insects, by contrast, eye development persists seemingly continuously from embryogenesis through the end of postembryogenesis. Comparative literature suggests that the evolutionary transition from continuous to biphasic eye development occurred via transient developmental arrest. This review investigates how the developmental arrest model relates to the gene networks regulating larval and adult eye development in Drosophila, and embryonic compound eye development in primitive insects. Consistent with the developmental arrest model, the available data suggest that the determination of the anlage of the rudimentary Drosophila larval eye is homologous to the embryonic specification of the juvenile compound eye in directly developing insects while the Drosophila compound eye primordium is evolutionarily related to the yet little studied stem cell based postembryonic eye primordium of primitive insects.     

Cuticle morphogenesis in crustacean embryonic and postembryonic stages

The crustacean cuticle is a chitin-based extracellular matrix, produced in general by epidermal cells and ectodermally derived epithelial cells of the digestive tract. Cuticle morphogenesis is an integrative part of embryonic and postembryonic development and it was studied in several groups of crustaceans, but mainly with a focus on one selected aspect of morphogenesis. Early studies were focused mainly on in vivo or histological observations of embryonic or larval molt cycles and more recently, some ultrastructural studies of the cuticle differentiation during development were performed. The aim of this paper is to review data on exoskeletal and gut cuticle formation during embryonic and postembryonic development in crustaceans, obtained in different developmental stages of different species and to bring together and discuss different aspects of cuticle morphogenesis, namely data on the morphology, ultrastructure, composition, connections to muscles and molt cycles in relation to cuticle differentiation. Based on the comparative evaluation of microscopic analyses of cuticle in crustacean embryonic and postembryonic stages, common principles of cuticle morphogenesis during development are discussed. Additional studies are suggested to further clarify this topic and to connect the new knowledge to related fields.     

Embryonic requirements for ErbB signaling in neural crest development and adult pigment pattern formation

Vertebrate pigment cells are derived from neural crest cells and are a useful system for studying neural crest-derived traits during post-embryonic development. In zebrafish, neural crest-derived melanophores differentiate during embryogenesis to produce stripes in the early larva. Dramatic changes to the pigment pattern occur subsequently during the larva-to-adult transformation, or metamorphosis. At this time, embryonic melanophores are replaced by newly differentiating metamorphic melanophores that form the adult stripes. Mutants with normal embryonic/early larval pigment patterns but defective adult patterns identify factors required uniquely to establish, maintain or recruit the latent precursors to metamorphic melanophores. We show that one such mutant, picasso, lacks most metamorphic melanophores and results from mutations in the ErbB gene erbb3b, which encodes an EGFR-like receptor tyrosine kinase. To identify critical periods for ErbB activities, we treated fish with pharmacological ErbB inhibitors and also knocked down erbb3b by morpholino injection. These analyses reveal an embryonic critical period for ErbB signaling in promoting later pigment pattern metamorphosis, despite the normal patterning of embryonic/early larval melanophores. We further demonstrate a peak requirement during neural crest migration that correlates with early defects in neural crest pathfinding and peripheral ganglion formation. Finally, we show that erbb3b activities are both autonomous and non-autonomous to the metamorphic melanophore lineage. These data identify a very early, embryonic, requirement for erbb3b in the development of much later metamorphic melanophores, and suggest complex modes by which ErbB signals promote adult pigment pattern development.     

The embryonic value of the micromeres in Ilyanassa obsoleta,as determined by deletion experiments. III. The third quartet cells and the mesentoblast cell, 4d

Summary

Each of the third quartet micromeres and the mesentoblast of the fourth quartet was removed and the effects on larval development analyzed. Removal of 3a resulted in a reduction in size of the left velar lobe. Removal of 3b resulted in a moderate reduction in size of the right velar lobe. Removal of 3c resulted in the absence of the right half of the foot and usually the right statocyst. Removal of 3d resulted in the absence of the left half of the foot and the left statocyst. Removal of both 3c and 3d resulted in the absence of the foot in most cases. Removal of the mesentoblast, 4d, resulted in the absence of the intestine, heart and larval kidney and various deficiencies of the midgut. On the basis of deletion experiments, each third quartet micromere and the mesentoblast is judged to have a specific embryonic value. The generally good development of the main ectodermal derivatives of the body following removal of the mesentoblast do not suggest any role for it or its derivatives as the primary organizer of the body axis and form.     

Gonadal Dysgenesis Reveals Sexual Dimorphism in the Embryonic Germline of Drosophila

In hybrid dysgenesis, sterility can occur in both males and females. At 27.5 degrees, however, we found that P element-induced germline death was restricted to females. This sex-specific gonadal dysgenesis (GD) is complete by the first larval instar stage. As such, GD at 27.5 degrees reveals the sexually dimorphic character of the embryonic germline. The only other known dimorphic trait of the embryonic germline is the requirement for ovo. ovo is required for germline development in females only and has been implicated in germline sex determination. Dominant mutations of ovo partially suppressed female GD. Although embryonic germ cells are undifferentiated and morphologically indistinguishable between males and females, the functional dimorphism seen in ovo requirement and GD at 27.5 degrees indicates that sexual identity in Drosophila germ cells is established in embryogenesis.