Lack of access to an open water source for bathing inhibited the development of the preen gland and preening behavior in Sanshui White ducks.

As a species of waterfowl, ducks rely on access to water to facilitate feeding behaviors. Further, wet preening behavior in ducks relies on access to water and is a key behavior for duck welfare. Traditionally, Chinese duck farms provide not only free access to drinking water in the duck house but also an open water pool outside of the house. However, recent restrictions prohibit the use of an open water pool for raising ducks in some areas of China. Little is known about the effects of not providing an open water pool on duck welfare, in particular, the development of the preen gland and wet preening behaviors. The preen gland secretes oil which is crucial for maintaining plumage conditions. A total of one hundred twenty 1-day-old Sanshui White ducks (SSWD) were randomly divided into 2 groups and fed for 6 wk with access to a water pool (WP) or without access to a water pool and provided drinking water only (LWP). The live body weights of ducks from the WP group were significantly increased compared with those of ducks in the LWP group starting from 3 wks of age (P < 0.05). Feed intake was increased in the WP group at 2 wk of age and from 4 to 6 wk of age (P < 0.05). The feed conversion ratio (FCR) was significantly different only at 4 and 5 wks of age, when the FCR was increased by 5.7% and 9.5%, respectively, in the LWP group compared with the WP group (P < 0.05). Lack of access to an open water pool significantly inhibited the growth of the preen gland based on its weight, size, and quantity of oil secretions (P < 0.05). In addition, the proportion of ducks exhibiting wet preening behavior was significantly reduced in the LWP group compared with the WP group (5.5 ± 0.2% vs. 24.8 ± 2.1%, P < 0.05). This study indicated that a lack of access to an open water source had negative impacts on the development of the preen gland and on the preening behavior of SSWD.

Developmental and transcriptomic features characterize defects of silk gland growth and silk production in silkworm naked pupa mutant.

The silkworm Bombyx mori is a well-characterized model organism for studying the silk gland development and silk production process. Using positional cloning and gene sequencing, we have previously reported that a truncated fibroin heavy chain was responsible for silkworm naked pupa (Nd) mutant. However, the mechanisms by which the mutant FibH causes developmental defects and secretion-deficiency of the silk gland remain to be fully elucidated. Here, silk gland's developmental features, histomorphology, and transcriptome analyses were used to characterize changes in its structure and gene expression patterns between Nd mutant and WT/Dazao. Whole larval stage investigation showed that Nd-PSG undergoes an arrested/delayed development, which eventually resulted in a gland degeneration. By using section staining and transmission electron microscope, a blockade in intracellular vesicle transport from endoplasmic reticulum to Golgi apparatus (secretion-deficiency) and an increased number of autophagosomes and lysosomes were found in Nd-PSG's cytoplasm. Next, by using RNA sequencing and comparative transcriptomic analysis, 2178 differentially expressed genes were identified between Nd-PSG and WT-PSG, among which most of the DEGs associated with cellular stress responses (autophagy, ubiquitin-proteasome system, and heat shock response) were significantly up-regulated in Nd-PSG, suggesting that mutant FibH perturbed cellular homeostasis and resulted in an activation of adaptive responses in PSG cells. These findings reveal the molecular mechanism of the Naked pupa (Nd) mutation and provide insights into silk gland development as well as silk protein production in silkworm Bombyx mori.

Fat body lipolysis connects poor nutrition to hypopharyngeal gland degradation in Apis mellifera.

The hypopharyngeal glands (HGs) of honey bee nurse workers secrete the major protein fraction of jelly, a protein and lipid rich substance fed to developing larvae, other worker bees, and queens. A hallmark of poorly nourished nurses is their small HGs, which actively degrade due to hormone-induced autophagy. To better connect nutritional stress with HG degradation, we looked to honey bees and other insect systems, where nutrient stress is often accompanied by fat body degradation. The fat body contains stored lipids that are likely a substrate for ecdysteroid synthesis, so we tested whether starvation caused increased fat body lipolysis. Ecdysteroid signaling and response pathways and IIS/TOR are tied to nutrient-dependent autophagy in honey bees and other insects, and so we also tested whether and where genes in these pathways were differentially regulated in the head and fat body. Last, we injected nurse-aged bees with the honey bee ecdysteroid makisterone A to determine whether this hormone influenced HG size and autophagy. We find that starved nurse aged bees exhibited increased fat body lipolysis and increased expression of ecdysteroid production and response genes in the head. Genes in the IIS/TOR pathway were not impacted by starvation in either the head or fat body. Additionally, bees injected with makisterone A had smaller HGs and increased expression of autophagy genes. These data support the hypothesis that nutritional stress induces fat body lipolysis, which may liberate the sterols important for ecdysteroid production, and that increased ecdysteroid levels induce autophagic HG degradation.

Fibroinase and its physiological inhibitors involved in the regulation of silk gland development in the silkworm, Bombyx mori.

Fibroinase, a cathepsin L-like cysteine protease, was previously identified in the silk gland of the silkworm, Bombyx mori. It shows high degradation activity during the pre-pupa period, when the silk gland undergoes apoptosis and remodeling. Here, we recombinantly expressed pro-fibroinase and activated it in vitro. Fibroinase showed optimal hydrolytic activity at pH 4.0 and its optimum temperature was about 42 °C. One physiological inhibitor, B. mori cysteine protease inhibitor (BCPI) was found, which showed strong inhibitory activity against fibroinase. The inhibitory reaction was caused by the formation of a non-covalent complex; this is in contrast to a previously reported mode of fibroinase inhibition by Serpin18. Expression profiles and immunolocalization analysis demonstrated that fibroinase was involved in silk gland development by degrading silk proteins and apoptosis/remodeling of silk glands at specific points. Furthermore, the comparison of the temporal expression of fibroinase and its inhibitors, BCPI and Serpin18, indicated that these inhibitors were involved in the silk gland development by regulating the activity of fibroinase from the fifth instar until the early spinning stage. These findings improve our understanding of the mechanism of protease regulation and its inhibitors in silk gland development.

Connecting the nutrient composition of seasonal pollens with changing nutritional needs of honey bee (Apis mellifera L.) colonies.

Free-ranging herbivores have yearly life cycles that generate dynamic resource needs. Honey bee colonies also have a yearly life cycle that might generate nutritional requirements that differ between times of brood rearing and colony expansion in the spring and population contraction and preparation for overwintering in the fall. To test this, we analyzed polyfloral mixes of spring and fall pollens to determine if the nutrient composition differed with season. Next, we fed both types of seasonal pollens to bees reared in spring and fall. We compared the development of brood food glands (i.e., hypopharyngeal glands - HPG), and the expression of genes in the fat body between bees fed pollen from the same (in-season) or different season (out-of-season) when they were reared. Because pathogen challenges often heighten the effects of nutritional stress, we infected a subset of bees with Nosema to determine if bees responded differently to the infection depending on the seasonal pollen they consumed. We found that spring and fall pollens were similar in total protein and lipid concentrations, but spring pollens had higher concentrations of amino and fatty acids that support HPG growth and brood production. Bees responded differently when fed in vs. out of season pollen. The HPG of both uninfected and Nosema-infected spring bees were larger when they were fed spring (in-season) compared to fall pollen. Spring bees differentially regulated more than 200 genes when fed in- vs. out-of-season pollen. When infected with Nosema, approximately 400 genes showed different infection-induced expression patterns in spring bees depending on pollen type. In contrast, HPG size in fall bees was not affected by pollen type, though HPG were smaller in those infected with Nosema. Very few genes were differentially expressed with pollen type in uninfected (4 genes) and infected fall bees (5 genes). Pollen type did not affect patterns of infection-induced expression in fall bees. Our data suggest that physiological responses to seasonal pollens differ between bees reared in the spring and fall with spring bees being significantly more sensitive to pollen type especially when infected with Nosema. This study provides evidence that seasonal pollens may provide levels of nutrients that align with the activities of honey bees during their yearly colony cycle. The findings are important for the planning and establishment of forage plantings to sustain honey bees, and in the development of seasonal nutritional supplements fed to colonies when pollen is unavailable.

Does size matter? Venom proteomic and functional comparison between night adder species (Viperidae: Causus) with short and long venom glands.

Night adders (Causus species within the Viperidae family) are amphibian specialists and a common source of snakebite in Africa. Some species are unique in that they have the longest venom glands of any viper, extending approximately 10% of the body length. Despite their potential medical importance and evolutionary novelty, their venom has received almost no research attention. In this study, venoms from a short-glanded species (C. lichtensteinii) and from a long-glanded species (C. rhombeatus) were compared using a series of proteomic and bioactivity testing techniques to investigate and compare the toxin composition and functioning of the venoms of these two species. Both C. rhombeatus and C. lichtensteinii were similar in overall venom composition and inhibition of blood coagulation through non-clotting proteolytic cleavage of fibrinogen. While the 1D gel profiles were very similar to each other in the toxin types present, 2D gel analyses revealed isoformic differences within each toxin classes. This variation was congruent with differential efficacy of South African Institute for Medical Research snake polyvalent antivenom, with C. lichtensteinii unaffected at the dose tested while C. rhombeatus was moderately but significantly neutralized. Despite the variation within toxin classes, the similarity in overall venom biochemistry suggests that the selection pressure for the evolution of long glands served to increase venom yield in order to subjugate proportionally large anurans as a unique form of niche partitioning, and is not linked to significant changes in venom function. These results not only contribute to the body of venom evolution knowledge but also highlight the limited clinical management outcomes for Causus envenomations.

Genes Integral to the Reproductive Function of Male Reproductive Tissues Drive Heterogeneity in Evolutionary Rates in Japanese Quail.

Early comparative genomics studies originally uncovered a nonintuitive pattern; genes involved in reproduction appeared to evolve more rapidly than other classes of genes. Currently, the emerging consensus is that genes encoding reproductive proteins evolve under variable selective pressures, producing more heterogeneous divergence patterns than previously appreciated. Here, we investigate a facet of that heterogeneity and explore the factors that drive male reproductive tissue-based heterogeneity in evolutionary rates. In Japanese quail (Coturnix japonica), genes with enriched expression in the testes evolve much more rapidly than those enriched in the foam gland (FG), a novel gland that secretes an airy foam that males transfer to females during mating. We compared molecular evolutionary patterns among (1) genes with induced expression in breeding vs. wintering conditions for both tissues and (2) genes that encode foam proteins (FPs) vs. those with varying degrees of expression specificity in the FG. We report two major findings. First, genes upregulated in breeding condition testes evolve exceptionally rapidly, while those induced in breeding condition FGs evolve slowly. These differences hold even after correcting for hormonally-dependent gene expression and chromosomal location. Second, genes encoding FPs are extremely conserved in terms of gene identity and sequence. Together, these finding suggest that genes involved in the reproductive function of each tissue drive the marked rate of heterogeneity.

Elevated expression of neuropeptide signaling genes in the eyestalk ganglia and Y-organ of Gecarcinus lateralis individuals that are refractory to molt induction.

Molting is induced in decapod crustaceans via multiple leg autotomy (MLA) or eyestalk ablation (ESA). MLA removes five or more walking legs, which are regenerated and become functional appendages at ecdysis. ESA eliminates the primary source of molt-inhibiting hormone (MIH) and crustacean hyperglycemic hormone (CHH), which suppress the production of molting hormones (ecdysteroids) from the molting gland or Y-organ (YO). Both MLA and ESA are effective methods for molt induction in Gecarcinus lateralis. However, some G. lateralis individuals are refractory to MLA, as they fail to complete ecdysis by 12weeks post-MLA; these animals are in the "blocked" condition. Quantitative polymerase chain reaction was used to quantify mRNA levels of neuropeptide and mechanistic target of rapamycin (mTOR) signaling genes in YO, eyestalk ganglia (ESG), thoracic ganglion (TG), and brain of intact and blocked animals. Six of the seven neuropeptide signaling genes, three of four mTOR signaling genes, and Gl-elongation factor 2 (EF2) mRNA levels were significantly higher in the ESG of blocked animals. Gl-MIH and Gl-CHH mRNA levels were higher in the TG and brain of blocked animals and levels increased in both control and blocked animals in response to ESA. By contrast, mRNA levels of Gl-EF2 and five of the 10 MIH signaling pathway genes in the YO were two to four orders of magnitude higher in blocked animals compared to controls. These data suggest that increased MIH and CHH synthesis in the ESG contributes to the prevention of molt induction by MLA in blocked animals. The up-regulation of MIH signaling genes in the YO of blocked animals suggests that the YO is more sensitive to MIH produced in the ESG, as well as MIH produced in brain and TG of ESA animals. Both the up-regulation of MIH signaling genes in the YO and of Gl-MIH and Gl-CHH in the ESG, TG, and brain appear to contribute to some G. lateralis individuals being refractory to MLA and ESA.

The function of heparan sulfate during branching morphogenesis.

Branching morphogenesis is a fundamental process in the development of diverse epithelial organs such as the lung, kidney, liver, pancreas, prostate, salivary, lacrimal and mammary glands. A unifying theme during organogenesis is the importance of epithelial cell interactions with the extracellular matrix (ECM) and growth factors (GFs). The diverse developmental mechanisms giving rise to these epithelial organs involve many organ-specific GFs, but a unifying paradigm during organogenesis is the regulation of GF activity by heparan sulfates (HS) on the cell surface and in the ECM. This primarily involves the interactions of GFs with the sulfated side-chains of HS proteoglycans. HS is one of the most diverse biopolymers and modulates GF binding and signaling at the cell surface and in the ECM of all tissues. Here, we review what is known about how HS regulates branching morphogenesis of epithelial organs with emphasis on the developing salivary gland, which is a classic model to investigate epithelial-ECM interactions. We also address the structure, biosynthesis, turnover and function of HS during organogenesis. Understanding the regulatory mechanisms that control HS dynamics may aid in the development of therapeutic interventions for diseases and novel strategies for tissue engineering and regenerative medicine.

Histomorphometric and transcriptomic features characterize silk glands' development during the molt to intermolt transition process in silkworm.

The molt-intermolt cycle is an essential feature in holometabolous and hemimetabolous insects' development. In the silkworm, silk glands are under dramatic morphological and functional changes with fibroin genes' transcription being repeatedly turned off and on during the molt-intermolt cycles. However, the molecular mechanisms controlling it are still unknown. Here, silk gland's histomorphology and transcriptome analysis were used to characterize changes in its structure and gene expression patterns from molt to intermolt stages. By using section staining and transmission electron microscope, a renewable cell damage was detected in the silk gland at the molt stage, and an increased number of autophagosomes and lysosomes were found in silk gland cells' cytoplasm. Next, by using RNA sequencing, 54,578,413 reads were obtained, of which 85% were mapped to the silkworm reference genome. The expression level analysis of silk protein genes and silk gland transcription factors revealed that fibroin heavy chain, fibroin light chain, P25/fhx, sericin1, sericin3 and Dimm had consistent alteration trends in temporal expression. In addition, differentially expressed genes (DEGs) were identified, and most of the DEGs associated with ecdysone signal transduction, mRNA degradation, protein proteolysis, and autophagy were significantly down-regulated in the transition from molt to intermolt, suggesting that these pathways were activated for the silk gland renewal. These findings provide insights into the molecular mechanisms of silk gland development and silk protein genes transcriptional regulation during the molt to intermolt transition process.

Conditional deletion of Sox17 reveals complex effects on uterine adenogenesis and function.

The importance of canonical Wnt signaling to murine uterine development is well established. Mouse models in which uterine-specific Wnt ligands, ß-catenin, or Lef1 are disrupted result in failure of postnatal endometrial gland development. Sox17 is a transcription factor characterized in numerous tissues as an antagonist of Wnt signaling. Thus, we hypothesized that conditional ablation of Sox17 would lead to hyperproliferation of endometrial glands in mice. Contrary to our prediction, disruption of Sox17 in epithelial and stromal compartments led to inhibition of endometrial adenogenesis and a loss of reproductive capacity. Epithelium-specific Sox17 disruption resulted in normal adenogenesis although reproductive capacity remained impaired. These findings suggest that non-epithelial, Sox17-positive cells are necessary for adenogenesis and that glands require Sox17 to properly function. To our knowledge, these findings are the first to implicate Sox17 in endometrial gland formation and reproductive success. The data presented herein underscore the importance of studying Sox17 in uterine homeostasis and function.

Morphological Changes in Skin Glands During Development in Rhinella Arenarum (Anura: Bufonidae).

Avoiding predation is critical to survival of animals; chemical defenses represent a common strategy among amphibians. In this study, we examined histologically the morphology of skin glands and types of secretions related to chemical skin defense during ontogeny of Rhinella arenarum. Prior to metamorphic climax the epidermis contains typical bufonid giant cells producing a mucous substance supposedly involved in triggering a flight reaction of the tadpole school. An apical layer of alcianophilic mucus covers the epidermis, which could produce the unpleasant taste of bufonid tadpoles. Giant cells disappear by onset of metamorphic climax, when multicellular glands start developing, but the apical mucous layer remains. By the end of climax, neither the granular glands of the dorsum nor the parotoid regions are completely developed. Conversely, by the end of metamorphosis the mucous glands are partially developed and secrete mucus. Adults have at least three types of granular glands, which we designate type A (acidophilic), type B (basophilic) and ventral (mucous). Polymorphic granular glands distribute differently in the body: dorsal granular glands between warts and in the periphery of parotoids contain protein; granular glands of big warts and in the central region of parotoids contain catecholamines, lipids, and glycoconjugates, whereas ventral granular glands produce acidic glycoconjugates. Mucous glands produce both mucus and proteins. Results suggest that in early juveniles the chemical skin defense mechanisms are not functional. Topographical differences in adult skin secretions suggest that granular glands from the big warts in the skin produce similar toxins to the parotoid glands.

Alkenyl sex pheromone analogs in the hemolymph of an arctiid Eilema japonica and several non-arctiid moths.

The majority of moth species utilize compounds derived from de novo synthesized fatty acids as their sex pheromones (type I). In contrast, species belonging to two recently diverged moth families, Arctiidae and Geometridae, utilize alkenes and their epoxides, which are derived from dietary essential fatty acids (EFAs), as their sex pheromones (type II). In the latter species, EFAs are considered to be converted into alkenes, often after chain elongation, in specialized cells called oenocytes. These alkenes are transported through the hemolymph to the pheromone gland, from which they are secreted with or without further modifications. We confirmed that the appearance of EFA-derived alkenes in the hemolymph was closely associated with the completion of pheromone gland formation in an arctiid moth Eilema japonica. Analyses of the hemolymph of several moth species utilizing type-I sex pheromones demonstrated the occurrence of (Z,Z,Z)-3,6,9-tricosatriene (T23), a typical type-II component, in the hemolymph of a noctuid Mamestra brassicae and two crambids Ostrinia furnacalis and Ostrinia scapulalis. Our results demonstrated that moths utilizing type-I pheromones have the ability to synthesize type-II sex pheromones, and suggested that recently diverged groups of moths may have secondarily exploited EFA-derived alkenes as sex pheromones.

Towards understanding the molecular basis of cockroach tergal gland morphogenesis. A transcriptomic approach.

The tergal gland is a structure exclusive of adult male cockroaches that produces substances attractive to the female and facilitates mating. It is formed de novo in tergites 7 and 8 during the transition from the last nymphal instar to the adult. Thus, the tergal gland can afford a suitable case study to investigate the molecular basis of a morphogenetic process occurring during metamorphosis. Using Blattella germanica as model, we constructed transcriptomes from male tergites 7-8 in non-metamorphosing specimens, and from the same tergites in metamorphosing specimens. We performed a de novo assembly all available transcriptomes to construct a reference transcriptome and we identified transcripts by homology. Finally we mapped all reads into the reference transcriptome in order to perform analysis of differentially expressed genes and a GO-enrichment test. A total of 5622 contigs appeared to be overrepresented in the transcriptome of metamorphosing specimens with respect to those specimens that did not metamorphose. Among these genes, there were six GO-terms with a p-value lower than 0.05 and among them GO: 0003676 ("nucleic acid binding") was especially interesting since it included transcription factors (TFs). Examination of TF-Pfam-motifs revealed that the transcriptome of metamorphosing specimens contains the highest diversity of these motifs, with 29 different types (seven of them exclusively expressed in this stage) compared with that of non-metamorphosing specimens, which contained 24 motif types. Transcriptome comparisons suggest that TFs are important drivers of the process of tergal gland formation during metamorphosis.

The embryonic origin of the ampullate silk glands of the spider Cupiennius salei.

Silk production in spiders is considered a key innovation, and to have been vital for the diversification of the clade. The evolutionary origin of the organs involved in spider silk production, however, and in particular of the silk glands, is poorly understood. Homologies have been proposed between these and other glands found in arachnids, but lacking knowledge of the embryonic development of spider silk glands hampers an evaluation of hypotheses. This study focuses on the embryonic origin of the largest silk glands of the spider Cupiennius salei, the major and minor ampullate glands. We show how the ampullate glands originate from ectodermal invaginations on the embryonic spinneret limb buds, in relation to morphogenesis of these buds. Moreover, we visualize the subsequent growth of the ampullate glands in sections of the early postembryonic stages. The invaginations are shown to correlate with expression of the proneural gene CsASH2, which is remarkable since it has been proposed that spider silk glands and their nozzles originate from sensory bristles. Hence, by confirming the ectodermal origin of spider silk glands, and by describing the (post-)embryonic morphogenesis of the ampullate glands, this work provides a starting point for further investigating into the genetic program that underlies their development.

Structure and development of male pheromone gland of longicorn beetles and its phylogenetic relationships within the tribe Clytini.

The male sex pheromone of the longicorn beetle, Xylotrechus pyrrhoderus pyrrhoderus Bates (Cerambycidae: Tribe Clytini) plays an important role in attracting females. This pheromone is produced by the pheromone gland located in the prothorax. However, the detailed structure and underlying developmental process of this gland are still unknown. We investigated the gland structure by using histological analysis and confirmed that the gland consists of the following parts: gland cell mass, a unique spherical space in the cuticle layer, and ductules connecting the gland cells with the spherical space and conducting canals to the outer opening. The gland structure first appeared male-specific in the late pupal stage, during which the epidermal cells began depositing the exocuticle; the development of the gland was completed after adult emergence. Furthermore, we verified the structural equivalents of the X. p. pyrrhoderus male pheromone gland in 11 species of 2 tribes, Clytini and Anaglyptini. The glands of these insects could be classified into four types on the basis of the absence or presence of the spherical space and the division of the gland cell mass layer. Most noteworthy, all the species with the spherical space and division-type gland were restricted to the Xylotrechus clade, as inferred from the molecular phylogenetic analysis. These results suggest that Clytini and Anaglyptini species share a fundamental process of male pheromone gland development, and that the Japanese Xylotrechus species might have established their current status by developing distinct structural features in the male pheromone gland.

Spermidine enhances the silk production by mulberry silkworm.

Polyamines are ubiquitous low molecular weight polycationic aliphatic amines involved in diverse cellular processes. Spermidine (Spd), a polyamine, has been proved to be crucial for cell survival in various organisms. Our study reports the effect of Spd on the growth of Bombyx mori. Silkworms showed improved silk gland weight and economic parameters in the fifth instar larval stage when treated with different concentrations of Spd, in the range of 25-75 µM. The worms treated with Spd produced 31% more silk when compared with the control worms. Altogether, this study establishes that Spd-treated leaves can be fed into the larvae for better silk production.

Serotonergic neurons respond to nutrients and regulate the timing of steroid hormone biosynthesis in Drosophila.

The temporal transition of development is flexibly coordinated in the context of the nutrient environment, and this coordination is essential for organisms to increase their survival fitness and reproductive success. Steroid hormone, a key player of the juvenile-to-adult transition, is biosynthesized in a nutrient-dependent manner; however, the underlying genetic mechanism remains unclear. Here we report that the biosynthesis of insect steroid hormone, ecdysteroid, is regulated by a subset of serotonergic neurons in Drosophila melanogaster. These neurons directly innervate the prothoracic gland (PG), an ecdysteroid-producing organ and share tracts with the stomatogastric nervous system. Interestingly, the projecting neurites morphologically respond to nutrient conditions. Moreover, reduced activity of the PG-innervating neurons or of serotonin signalling in the PG strongly correlates with a delayed developmental transition. Our results suggest that serotonergic neurons form a link between the external environment and the internal endocrine system by adaptively tuning the timing of steroid hormone biosynthesis.

Age-dependent changes in ultrastructure of the defensive glands of Neocapritermes taracua workers (Isoptera, Termitidae).

Protection against predators and competitors is one of the main concerns of termite colonies, which developed a specialised defensive caste, the soldiers. However, soldiers are rare or even missing in several lineages of termites, while workers often develop new defence strategies especially in soil-feeding species. Here, we describe the morphology and ultrastructure of the autothysis-associated glands of Neocapritermes taracua workers and report their age-related changes in structure. The defensive glands of N. taracua workers consist of a pair of labial and a pair of crystal glands, whose secretions mix together through autothysis. Autothysis always occurs at the line of weakness connecting the anterior parts of the crystal-bearing pouches. The crystal glands consist of groups of bicellular secretory units (secretory and corresponding canal cells) which secrete the blue crystal material into external pouches. Their secretory activity is maximal in the middle of worker life, and is considerably lower in very young and old workers. The labial glands are composed of two types of secretory cells: the central and the parietal cells. While the central cells are developed similarly to other termites and secrete proteinaceous secretion into labial gland ducts, the parietal cells develop proteinaceous granules which may eventually bud off the cells. The secretory function of parietal cells is so far unique to N. taracua and differs from other termite species in which they are only responsible of water uptake by acini. The defensive device of N. taracua is truly exceptional as it involves a new gland and a previously undescribed function for parietal cells, being a remarkable example of evolution of morphological innovation.

Ultrastructure, functional morphology and evolution of recto-canal epidermal glands in Myriapoda.

In Chilopoda, solitary epidermal glands are composed of a couple of cells only. These glands are highly abundant on the entire body surface and are distributed throughout the single-layered epidermis. Some authors provided more or less comprehensive observations on the structure of epidermal glands of specific chilopod taxa. However, no information is hitherto available on the ultrastructural diversity of these glands. Furthermore, potential homologies of these chilopod epidermal glands and of their characteristic cellular components remain unknown. Based on our results, we are now able to distinguish two types of epidermal glands in Chilopoda that can be clearly distinguished by their structure and the course of their conducting canal: recto-canal epidermal glands (rceg) and flexo-canal epidermal glands (fceg). In the present paper, we focus on the rceg. We examined the ultrastructural organization of these glands in the head region and on the anterior trunk segments of various representatives of the five extant chilopod orders by light- and electron-microscopy. According to our terminology, rceg consist of up to five different cell types including: a) distal canal cells, b) proximal canal cells, c) intermediary cells, and d) two different types of secretory cells. Intermediary and canal cells form a common conducting canal. The rceg may taxon-specifically differ in relative size and subcellular architecture, but all have the following features in common: 1) a wide distribution on various body regions among all five chilopod subtaxa, 2) the straight, broad and locally dilated conducting canal surrounded by closely packed microvilli or microvilliform infoldings around the apex of the canal cell(s), and 3) the tendency to aggregate to form compound glandular organs of massive size and complexity. Tricellular glandular units established by three different cell types are observed in Scutigeromorpha and Geophilomorpha, whereas four cell types constitute rceg in Lithobiomorpha and Craterostigmomorpha. Five different cell types per glandular unit are found only in Scolopendromorpha. The partial cuticularization of the lower part of the conducting canal formed by the intermediary cell, as found in Chilopoda, differs from the pattern described for equivalent euarthropod epidermal glands, as for instance in Hexapoda. Their wide distribution in Chilopoda and Progoneata makes it likely that tricellular rceg were at least present in the last common ancestor of the Myriapoda. Concerning Chilopoda, the evolution of highly diverse rceg is well explained on the basis of the Pleurostigmophora concept. Glands of the recto-canal type are also found in other arthropods. The paper discusses cases where homology of rceg and also fceg may be assumed beyond Myriapoda and briefly evaluates the potentials and the still-to-be-solved issues prior to use them as an additional character system to reconstruct the phylogeny of the Euarthropoda.