The Drosophila fork head factor directly controls larval salivary gland-specific expression of the glue protein gene Sgs3.

The Drosophila Fork head protein participates in salivary gland formation, since salivary glands are missing in fork head embryos. Here we show that the fork head encoded protein binds to an upstream regulatory region of the larval salivary gland glue protein gene Sgs3. Mobility shift assay in the presence of an anti-Fork head antibody demonstrated that the Fork head factor interacts with the TGTTTGC box shown to be involved in tissue-specific Sgs3 expression. Experiments employing a set of oligonucleotide competitors revealed that Fork head binding was prevented by the same single base substitutions that were previously shown to interfere with the TGTTTGC element function in vivo. Furthermore, the anti-Fork head antibody bound to >60 sites of polytene chromosomes, including the puffs of all Sgs genes and Fork head protein was detected in the nuclei of salivary glands of larvae of all examined stages. These data provide experimental evidence for the hypothesis that the protein encoded by the fork head gene is required initially for salivary gland formation and is utilized subsequently in the control of larval genes specifically expressed in this organ.     

The larval head anatomy of Rhyacophila (Rhyacophilidae) with discussion on mouthpart homology and the groundplan of Trichoptera

The external and internal features of the larval head of Rhyacophila fasciata (Trichoptera: Rhyacophilidae) were described in detail. Anatomical examinations were carried out using a multimethod approach including histology, scanning electron microscopy, confocal laser‐scanning microscopy, microcomputed tomography, and computer‐based three‐dimensional reconstructions. Additionally, the information on the larval head of Limnephilus flavicornis (Limnephilidae) and Hydropsyche angustipennis (Hydropsychidae) available in the literature were reinvestigated. These anatomical data were used to address major questions of homology and terminology, that is, the ventral closure of the head capsule, the sclerites, and appendages of labium and maxilla and their muscles. These topics were discussed by summarizing the main hypotheses present in the literature and a critical inclusion of new findings. Consequently, the inner lobe of the maxilla very likely represents the galea. The distal maxillary sclerite (palpifer) is an anatomical composite formation at least including dististipes and lacinia. Based on these homology hypotheses several potential groundplan features of the larval head of Trichoptera were reconstructed. The head of Rhyacophila shows several presumably plesiomorphic features as for instance the prognath orientation of the mouthparts, the well‐developed hypocranial bridge, the triangular submentum and eyes composed of seven stemmata. Derived features of Rhyacophila are the reduced antennae, the anterior directing of three stemmata and the shift of the tentorio‐stipital muscle to the mentum. J. Morphol. 276:1505–1524, 2015. © 2015 Wiley Periodicals, Inc.     

Scale formation in selected fundulid and cyprinodontid fishes

Patterns of scale formation (onset, points of origin, completion, and spatial pattern) were examined for six species of killifishes in two families (Cyprinodontidae: Cyprinodon variegatus, and Fundulidae: Fundulus confluentus, F. heteroclitus, F. luciae, F. majalis, and Lucania parva) to determine if the patterns are another useful indicator for the transition from the larval to juvenile periods. In some species, the patterns were very similar, with scale formation originating on/near the caudal peduncle, then the dorsal surface of the head (in fundulids only), and later on the lateral surfaces of the head, and on the ventral surface of the trunk at the level of the pectoral fin. The timing of scale formation, relative to fish size, was later than or overlapped with other morphological characters (e.g., fin ray formation, juvenile/adult body shape) often used to mark the larval/juvenile transition. The onset of scale formation, across all species, occurred between 8 and 13 mm TL. Completion of scale formation occurred between 18 and 23 mm TL. At completion, scales covered 86–99% of the trunk and head. Completion of scale formation in these fishes is one of the last external morphological changes to occur during the larval to juvenile transition. For these species, and other flatfishes we have examined in detail, it appears that scale formation may be useful in helping to define the end of the larval period and the beginning of the juvenile period. Further studies, of divergent groups of teleosts, are necessary to determine if this length-based approach has broad validity.     

Testing the evolutionary constraints of metamorphosis: The ontogeny of head shape in Triturus newts

In vertebrates with complex, biphasic, life cycles, larvae have a distinct morphology and ecological preferences compared to metamorphosed juveniles and adults. In amphibians, abrupt and rapid metamorphic changes transform aquatic larvae to terrestrial juveniles. The main aim of this study is to test whether, relative to larval stages, metamorphosis (1) resets the pattern of variation between ontogenetic stages and species, (2) constrains intraspecific morphological variability, and (3) similar to the “hour‐glass” model reduces morphological disparity. We explore postembryonic ontogenetic trajectories of head shape (from hatching to completed metamorphosis) of two well‐defined, morphologically distinct Triturus newts species and their F1 hybrids. Variation in head shape is quantified and compared on two levels: dynamic (across ontogenetic stages) and static (at a particular stage). Our results show that the ontogenetic trajectories diverge early during development and continue to diverge throughout larval stages and metamorphosis. The high within‐group variance and the largest disparity level (between‐group variance) characterize the metamorphosed stage. Hence, our results indicate that metamorphosis does not canalize head shape variation generated during larval development and that metamorphosed phenotype is not more constrained relative to larval ones. Therefore, metamorphosis cannot be regarded as a developmental constraint, at least not for salamander head shape.     

Analysis of the shortvein cis-regulatory region of the decapentaplegic gene of Drosophila melanogaster

In mammals, the Transforming Growth Factor-beta (TGF-beta) superfamily controls a variety of developmental processes. In Drosophila, by contrast, a single member of the superfamily, decapentaplegic (dpp) performs most TGF-beta developmental functions. The complexity of dpp functions is reflected in the complex cis-regulatory sequences that flank the gene. Dpp is divided into three regions: Hin, including the protein-coding exons; disk, including 3' cis-regulatory sequences; and shortvein (shv), including noncoding exons and 5' cis-regulatory sequences. We analyzed the cis-regulatory structure of the shortvein region using a nested series of rearrangement breakpoints and rescue constructs. We delimit the molecular regions responsible for three mutant phenotypes: larval lethality, wing venation defects, and head capsule defects. Multiple overlapping elements are responsible for larval lethality and wing venation defects. However, the area regulating head capsule formation is distinct, and resides 5' to these elements. We have demonstrated this by isolating and describing two novel dpp alleles, which affect only the adult head capsule.     

Photoperiodic induction of diapause in the silkworm, Bombyx mori: location of the photoreceptor using a chemiluminescent paint

ABSTRACT. To locate the photoreceptor involved in the photoperiodic induction of diapause in Bombyx mori L., covering of larval head with black paint or local illumination using chemiluminescent paint was carried out. A silkworm race showing a response of long-day type during the larval stage was employed. The results demonstrated that the photoreceptor is located in the head but is extraocular. The optical properties of the larval body suggest that during the first and second stadia light is admitted through the translucent clypeus of the head, but during later stadia enters over the entire larval body including the head, and that it reaches the cerebral lobe where a photoreceptor is possibly located.     

Organization of the Drosophila head as revealed by the ectopic expression of the Ultrabithorax product.

By using a hsp70-Ubx fusion gene, we have ectopically expressed a Ubx product in the embryonic head primordia and studied the developmental effects on the larval head. We find that after high and persistent levels of Ubx product, the head is replaced by three (C1, C2 and C3) abdominal-like denticle belts. The C2 and C3 belts are the homeotic transformations of parasegments 1 and 2, respectively, while the C1 belt probably derives from the transformation and subsequent fusion of the most anterior procephalic primordia. On the basis of their response to the Ubx product and other arguments, we propose that the larval head is made of two genetically distinct components; one is the procephalon and the anterior region of the mandibular lobe, and the other is part of the parasegmental trunk and includes parasegments 1 and 2. Our results also indicate that most or all the larval head structures derive from precursor cells of ventral origin.     

Ultrastructure and significance of the transitory nephridia in Erpobdella octoculata (Hirudinea, Annelida)

In early developmental stages of Erpobdella octoculata two pairs of transitory nephridia occur which degenerate during the formation of the body segments. Because in the ground pattern of Annelida the first nephridia formed during ontogenesis are protonephridia, it can be assumed that the transitory nephridia of E. octoculata are homologous to the larval protonephridia (head kidneys) of Polychaeta. To test this hypothesis two cryptolarvae of E. octoculata were investigated ultrastructurally. Both pairs of transitory nephridia are serially arranged to either side of the midgut vestigium. Each organ consists of a coiled duct that opens separately to the exterior by an intraepidermal nephridiopore cell. The duct is percellular and formed by seventeen cells. Adluminal adherens and septate junctions connect all duct cells; the most proximal duct cell completely encloses the terminal end of the duct lumen. A filtration structure characteristic for protonephridia is lacking. Additionally, the entire organ lacks an inner ciliation. Morphologically and ultrastructurally the transitory nephridia of E. octoculata show far reaching congruencies with the segmental metanephridia in different species of the Hirudinea. These congruencies support the assumption that formation of transitory nephridia and definitive metanephridia in Hirudinea depends on the same genetic information. The same inherited information is assumed to cause the development of larval head kidneys and subsequently formed nephridia in different species of the Polychaeta. Thus, the presumed identical fate of a segmentally repeated nephridial anlage supports the hypothesis of a homology between the transitory nephridia in Hirudinea species and the protonephridial head kidneys in the ground pattern of the Polychaeta. We, therefore, assume that functional constraints lead to a modification of the protonephridial head kidneys in Hirudinea and explain ultrastructural differences between the transitory nephridia in Hirudinea and the protonephridia in Polychaeta. Accepted: 11 December 2000     

绿豆象幼虫虫龄的划分及末龄幼虫头部形态和感器观察

【目的】明确绿豆象Callosobruchus chinensis幼虫的龄期,了解其末龄幼虫头部感受器的种类、形态和分布。【方法】测量绿豆象幼虫体长、头壳宽和上颚宽,根据所得数据的频次分布图、关系拟合结果和戴氏法则确定绿豆象最佳分龄指标,明确幼虫虫龄数,并利用Crosby生长法则和线性回归的方法进行验证;采用扫描电镜对末龄幼虫头部形态及感受器进行观察。【结果】绿豆象体长、头壳宽和上颚宽的频次分布均呈显著的4个峰,因此推断绿豆象幼虫为4个虫龄。各龄的体长变幅分别为1.581～2.556, 2.406～3.381, 3.381～4.281和4.206～4.881 mm,头壳宽度变幅分别为0.444～0.689, 0.654～0.934, 0.934～1.179和1.144～1.389 mm,上颚宽变幅分别为0.080～0.256, 0.234～0.344, 0.322～0.542和0.542～0.652 mm。体长、头壳宽和上颚宽均符合戴氏法则和Crosby生长法则,并呈现明显的线性关系,因此体长、头壳宽和上颚宽可作为绿豆象幼虫龄期划分的重要指标。头壳宽的Crosby指数均小于体长和上颚宽的Crosby指数,且头壳宽与体长测量值的对数值与幼虫龄期的相关系数要优于上颚宽测量值的对数值与幼虫龄期的相关系数,因此可将头壳宽作为最佳分龄指标。绿豆象末龄幼虫头部感器共有锥形感器、毛形感器、瓶形感器、刺形感器、板形感器、栓锥形感器和坛形感器7种感器,主要分布于触角、下颚须、上唇和上颚。【结论】绿豆象幼虫分龄形态指标和头部形态观察为研究其行为活动及综合防治提供理论基础。     

虫酰肼对甜菜夜蛾多巴脱羧酶和酪氨酸羟化酶的抑制作用

虫酰肼模拟昆虫蜕皮激素的作用干扰新表皮的形成。为了探讨虫酰肼对昆虫新表皮形成的影响是否与抑制表皮形成相关酶的活性有关, 本研究应用高效液相色谱-荧光检测法（HPLC-RP）, 测定了甜菜夜蛾Spodoptera exigua 5龄幼虫用虫酰肼处理不同时间（24, 48和72 h）后多巴脱羧酶和酪氨酸羟化酶的活性。结果表明： 用LC₁₁ （28.41 μmol/L）和LC₃₃ （85.23 μmol/L）两个亚致死剂量的虫酰肼处理5龄幼虫后, 多巴脱羧酶和酪氨酸羟化酶的活性均受到明显抑制, 高浓度的抑制作用大于低浓度的抑制作用。随着处理时间的延长, 同一剂量的抑制作用逐渐增强。进一步测定虫酰肼处理24, 48和72 h后5龄幼虫血淋巴、 脂肪体、 中肠、 表皮和头部的多巴脱羧酶和酪氨酸羟化酶的活性, 可看出虫酰肼对幼虫不同组织的多巴脱羧酶和酪氨酸羟化酶的活性也具有相似的抑制作用。结果提示, 虫酰肼对甜菜夜蛾幼虫多巴脱羧酶和酪氨酸羟化酶活性具有明显抑制作用, 幼虫新表皮形成受阻可能与虫酰肼抑制多巴脱羧酶和酪氨酸羟化酶的活性有关。     

Head shape variation in cerambycid saproxylic beetles as a function of host plant selection

Saproxylic insects depend on deadwood for larval development, and a certain degree of specialization may be involved in their choice of host plants and/or wood in a particular stage of degradation. The plant species chosen for oviposition in turn act as an environmental pressure on the head morphology of larvae and it is expected that head shape plasticity varies directly with the number of woody plant species used for larval development in each insect species. We analyzed head shape variation in saproxylic beetles with respect to host plant species, maximum time of larval emergence and season of the year when insects colonized branches. Generalist species in the use of host plants showed significant variation in head shape and size. Time of emergence and season did not appear to affect head shape, although season was a determinant factor of abundance and possibly head size variation.     

Expression of en and wg in the embryonic head and brain of Drosophila indicates a refolded band of seven segment remnants.

Based on the expression pattern of the segment polarity genes engrailed and wingless during the embryonic development of the larval head, we found evidence that the head of Drosophila consists of remnants of seven segments (4 pregnathal and 3 gnathal) all of which contribute cells to neuromeres in the central nervous system. Until completion of germ band retraction, the four pregnathal segment remnants and their corresponding neuromeres become arranged in an S-shape. We discuss published evidence for seven head segments and morphogenetic movements during head formation in various insects (and crustaceans).     

Development of the musculature in the limpet Patella (Mollusca, Patellogastropoda)

 Whole-mount technique using fluorescent-labelled phalloidin for actin staining and confocal laser scanning microscopy as well as semi-thin serial sectioning, scanning and transmission electron microscopy were applied to investigate the ontogeny of the various muscular systems during larval development in the limpets Patella vulgata L. and P. caerulea L. In contrast to earlier studies, which described a single or two larval shell muscles, the pretorsional trochophore-like larva shows no less than four different muscle systems, namely the asymmetrical main head/foot larval retractor muscle, an accessory larval retractor with distinct insertion area, a circular prototroch/velar system, and a plexus-like pedal muscle system. In both Patella species only posttorsional larvae are able to retract into the shell and to close the aperture by means of the operculum. Shortly after torsion the two adult shell muscles originate independently in lateral positions, starting with two fine muscle fibres which insert at the operculum and laterally at the shell. During late larval development the main larval retractor and the accessory larval retractor become reduced and the velar muscle system is shed. In contrast, the paired adult shell muscles and the pedal muscle plexus increase in volume, and a new mantle musculature, the tentacular muscle system, and the buccal musculature arise. Because the adult shell muscles are entirely independent from the various larval muscular systems, several current hypotheses on the ontogeny and phylogeny of the early gastropod muscle system have to be reconsidered. Received: 23 June 1998 / Accepted: 25 November 1998     

Lens-forming competence in the epidermis of Xenopus laevis during development

In larval X. laevis the capacity to regenerate a lens under the influence of inductive factors present in the vitreous chamber is restricted to the outer cornea and pericorneal epidermis (Lentogenic Area, LA). However, in early embryos, the whole ectoderm is capable of responding to inductive factors of the larval eye forming lens cells. In a previous paper, Cannata et al. (2003) demonstrated that the persistence of lens-forming competence in the LA is the result of early signals causing lens-forming bias in the presumptive LA and of late signals from the eye causing cornea development. This paper analyzes 1) the decrease of the lens-forming capacity in ectodermal regions both near LA (head epidermis) and far from LA (flank epidermis) during development, 2) the capacity of the head epidermis and flank epidermis to respond to lens-competence promoting factors released by an eye transplanted below these epidermal regions, and 3) the eye components responsible for the promoting effect of the transplanted eye. Results were obtained by implanting fragments of ectoderm or epidermis into the vitreous chamber of host tadpoles and by evaluating the percentage of implants positive to a monoclonal antibody anti-lens. These results demonstrated that the lens-forming competence in the flank region is lost at the embryonic stage 30/31 and is weakly restored by eye transplantation; however, lens-forming competence in the head region is lost at the larval stage 48 and is strongly restored by eye transplantation. The authors hypothesize that during development the head ectoderm outside the LA is attained by low levels of the same signals that attain the LA and that these signals are responsible for the maintenance of lens-forming competence in the cornea and pericorneal epidermis of the larva. In this hypothesis, low levels of these signals slacken the decrease of the lens-forming competence in the head ectoderm and make the head epidermis much more responsive than the flank epidermis to the effect of promoting factors released by a transplanted eye. Results obtained after transplantation of eyes deprived of some components indicate that the lens and the retina are the main source of these promoting factors. The immunohistochemical detection of the FGFR-2 (bek variant) protein in the epidermis of stage 53 larvae submitted to eye transplantation at stage 46 showed that the eye transplantation increased the level of FGFR-2 protein in the head epidermis but not in the flank epidermis, indicating that the lens-forming competence in X. laevis epidermis could be related to the presence of an activated FGF receptor system in the responding tissue.     

Retinal development in the lamprey (Petromyzon marinus L.): premetamorphic ammocoete eye.

Development of the retina of the ammocoete begins early in embryogenesis, with the formation of the optic vesicle, but development of the rudimentary eye is suspended and remains arrested during larval life. Prior to the onset of metamorphosis, the retina of the ammocoete is completely undifferentiated, with the exception of a small area (Zone II) surrounding the optic nerve head, where all of the adult retinal layers are found. The photoreceptors in this area have developed to include synaptic contacts as well as inner and outer segments. The pigment epithelium in this area, too, has differentiated to include well-formed melanin granules, myeloid bodies and endoplasmic reticulum and is closely associated with the receptor cell outer segments. With the approach of metamorphosis, differentiation of the remainder of the retina (Zone I) begins, taking place in a radial fashion from the optic nerve head. Differentiating pigment epithelial cells adjacent to the differentiated retinal zone begin to accumulate melanin granules. In the neural retina, junctional complexes are established in the form of an external limiting membrane, and connecting cilia project into the optic ventricle. Photoreceptor differentiation begins with the formation of a mitochondria-filled ellipsoid within the inner segment. Development and differentiation of the ammocoete retina is unique to vertebrates in that only a small area of differentiated retina is present during the larval stage. The remainder of the retina differentiates and becomes functional during metamorphosis.     

A Model of Drosophila Larva Chemotaxis

Detailed observations of larval Drosophila chemotaxis have characterised the relationship between the odour gradient and the runs, head casts and turns made by the animal. We use a computational model to test whether hypothesised sensorimotor control mechanisms are sufficient to account for larval behaviour. The model combines three mechanisms based on simple transformations of the recent history of odour intensity at the head location. The first is an increased probability of terminating runs in response to gradually decreasing concentration, the second an increased probability of terminating head casts in response to rapidly increasing concentration, and the third a biasing of run directions up concentration gradients through modulation of small head casts. We show that this model can be tuned to produce behavioural statistics comparable to those reported for the larva, and that this tuning results in similar chemotaxis performance to the larva. We demonstrate that each mechanism can enable odour approach but the combination of mechanisms is most effective, and investigate how these low-level control mechanisms relate to behavioural measures such as the preference indices used to investigate larval learning behaviour in group assays.     

The morphology of the larval head of Tipulidae (Diptera, Insecta) - The dipteran groundplan and evolutionary trends

External and internal head structures of the larva of Tipula montium are described in detail. The results are compared to conditions found in other representatives of Tipuloidea and other dipteran and antliophoran lineages. Despite of the conceivably basal position of Tipulomorpha within Diptera, the larvae are mainly characterised by derived features. The partially retracted head, the specific hemicephalic condition and several other derived character states support the monophyly of Tipuloidea. A clade comprising Tipuloidea excluding Pediciidae is suggested by the strongly retracted head, by deep dorsolateral incisions of the head capsule, by a distinctly toothed anterior premental margin, by the loss of the second extrinsic maxillary muscle, and possibly by the loss of the pharyngeal filter. Eriopterinae and Hexatominae are characterised by a tendency towards an extreme reduction of the head capsule. Limoniinae, Cylindrotomidae, and Tipulidae form a clade supported by the presence of a premaxillary suture. This implies the non-monophyly of Limoniidae. A feature shared by Cylindrotomidae and Tipulidae is the presence of a movable lacinia mobilis. However, this is arguably a plesiomorphic feature, as it also occurs in Nannochoristidae. Features of the larval head of Trichoceridae, which were included in Tipulomorpha, do not show affinities with those of Tipuloidea. Trichocerid larvae share a specialised subdivided mandible with larvae of psychodomorph groups. Tipuloidea are a highly specialised group. The characters examined did not reveal plesiomorphic features supporting a basal position, and features suggesting closer affinities with Brachycera are vague. The evolution of dipteran larval head structures was apparently strongly affected by the loss of legs and the tendency to live in cryptic habitats. Diptera are the group of Endopterygota with the highest number of apomorphic features of the larval head. The appendages are generally simplified and the muscular apparatus is strongly reduced. Specialised features evolving within dipteran lineages include specifically arranged brushes of hairs on the labrum and epipharynx, movable messores, subdivided mandibles, different mandibular brushes, and a far-reaching reduction of labial parts.     

First μ‐CT‐based 3D reconstruction of a dipteran larva—the head morphology of protanyderus (tanyderidae) and its phylogenetic implications

The larval head of Protanyderus was examined and documented using innovative techniques, with emphasis on internal structures. A chart listing all head muscles of dipteran larvae and other holometabolan groups is presented in the Supporting Information. The results are compared to conditions found in other nematoceran lineages. The larval head of Protanyderus is characterized mainly by plesiomorphic character states such as the complete and largely exposed head capsule, the long coronal suture, V‐shaped frontal sutures, lateral antennal insertion areas, a transverse labrum, a nearly horizontal plane of mandibular movements, mandibles lacking a movable distal part, a mesal hook and mesal or distal combs, separated maxillary endite lobes, a comparatively complete array of muscles, and a brain only partly located within the head capsule. An anteriorly toothed hypostomal plate and dense labral brushes of microtrichiae are also likely groundplan features of Diptera. The pharyngeal filter is a possible apomorphy of Diptera excl. Deuterophlebiidae (or Deuterophlebiidae + Nymphomyiidae). The messors have also likely evolved early in the dipteran crown group but are absent in the groundplan. The phylogenetic interpretation of externolateral plates with growth lines is ambiguous. Autapomorphies of Tanyderidae are differences between the third and fourth instar larvae, the roof‐like extension above the antennal insertion area, the dorsal endocarina, and the posterodorsal internal ridge. The phylogenetic position of Tanyderidae is controversial, but features of the larval head do not support a proposed sistergroup relationship between Tanyderidae and Psychodidae. Both groups differ in many features of the larval head, and we did not identify a single potential synapomorphy. Larval characters alone are insufficient for a reliable phylogenetic reconstruction, though they vary greatly and apparently contain phylogenetic information. The evaluation of these features in the context of robust molecular phylogenies will be a sound basis for the reconstruction of complex evolutionary scenarios for the megadiverse Diptera. Diptera. J. Morphol. 2012. © 2012 Wiley Periodicals, Inc.