Frontal Gland Research Articles

The frontal gland in workers of Neotropical soldierless termites

The presence of the frontal gland is well established in termite soldiers of Rhinotermitidae, Serritermitidae, and Termitidae. It is one of their main defensive adaptations or even an exclusive weapon. The gland was also occasionally reported in alate imagoes, but never in the worker caste. Here, we report the first observation of a frontal gland in workers of several Neotropical and one African species of Apicotermitinae. The ultrastructure of Aparatermes cingulatus and Anoplotermes nr. subterraneus is described in detail. In these two species, the gland is well-developed, functional and consists of class 1 secretory cells. The presence of envelope cells, wrapping the gland, is an unusual feature, as well as the presence of several zonulae adherens, connecting neighbouring glandular cells. The frontal gland of workers is homologous to this organ in soldiers and imagoes, as evidenced by the same position in the head and its connection to the same muscle. However, the defensive role of the frontal gland in workers remains to be confirmed.

Temporal and geographic variations in the morphology and chemical composition of the frontal gland in imagoes of Prorhinotermes species (Isoptera: Rhinotermitidae)

Although the frontal gland has long been known as a prominent defensive device for termite soldiers in many Rhinotermitidae and Termitidae, almost nothing is known about its function in imagoes. In the present study, we show that the frontal gland of imagoes in Prorhinotermes species is well developed at the time of the nuptial flight, and is filled with a complex mixture of sesquiterpene hydrocarbons and nitroalkenes. The sesquiterpene composition varies between Prorhinotermes simplex and Prorhinotermes canalifrons, between geographically distant colonies of P. simplex (Cuba versus Florida), and even between different flights of closely-related subcolonies. The ratio between (E)-1-nitropentadec-1-ene and sesquiterpenes is sex-specific. The volume of secretory cells decreases in functional kings and queens after colony foundation, and the subcellular organization changes into a form resembling unmodified epidermal cells. Dealate reproductives lose the ability for biosynthesis, and their frontal gland is devoid of volatile compounds found in swarming imagoes. The results obtained in the present study clearly show that the frontal gland is only temporarily active at the time of the dispersal flight. The most likely function of this gland is defence by the toxic nitroalkenes. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98, 384–392.

Reconstruction of Middle Third Defects of the Face With the Temporal Flap

The temporal flap is of great interest in head and neck reconstruction when a skin graft or a local flap cannot be used. It has shown important results on the facial reanimation and in oncological surgery. We describe our experience with the pedicled flap in reconstruction of the middle third face defects in 8 oncologic patients. This flap allows the covering of bone and noble structures such as the periorbital, auricular, frontal, or parotid gland areas. Few major or minor complications were seen and good aesthetic results were achieved. It also can be done with or without adjuvant radiotherapy. The patient prognosis however, depends on the stage of the tumor.

Presoldier Induction by a Juvenile Hormone Analog in the Nasute TermiteNasutitermes takasagoensis(Isoptera: Termitidae)

The ability of JHIII and three JHAs (hydroprene, pyriproxyfen and methoprene) to induce presoldier differentiation was tested in a highly derived termite, Nasutitermes takasagoensis (Isoptera: Nasutitermitinae), and induced presoldiers were examined morphologically and histologically. Hydroprene was the most effective hormone analog for the artificial induction of presoldier differentiation. Principal component analysis showed that hydroprene-induced presoldiers had similar external gross morphology to natural presoldiers found in the same colony. Induced presoldiers had a long, horn-like frontal projection, called a nasus, on the head. A well-developed reservoir and duct of the frontal gland were also observed inside the head. Scanning electron micrographs showed that the precursory structure forming the nasus (nasus disc) was developed under the cuticle of hydroprene-treated individuals just prior to the molt into presoldiers. Morphological changes in presoldier differentiation induced by hydroprene seemed to occur normally, compared with those in natural presoldiers. Thus, the present methods shown in this study will provide opportunities to conduct further molecular analyses on the molecular developmental bases of nasus formation during soldier differentiation in higher termites.

(E,E)-α-Farnesene, an Alarm Pheromone of the Termite Prorhinotermes canalifrons

The behavioral and electroantennographic responses of Prorhinotermes canalifrons to its soldier frontal gland secretion, and two separated major components of the secretion, (E)-1-nitropentadec-1-ene and (E,E)-alpha-farnesene, were studied in laboratory experiments. Behavioral experiments showed that both the frontal gland secretion and (E,E)-alpha-farnesene triggered alarm reactions in P. canalifrons, whereas (E)-1-nitropentadec-1-ene did not affect the behavior of termite groups. The alarm reactions were characterized by rapid walking of activated termites and efforts to alert and activate other members of the group. Behavioral responses to alarm pheromone differed between homogeneous and mixed groups, suggesting complex interactions. Antennae of both soldiers and pseudergates were sensitive to the frontal gland secretion and to (E,E)-alpha-farnesene, but soldiers showed stronger responses. The dose responses to (E,E)-alpha-farnesene were identical for both soldiers and pseudergates, suggesting that both castes use similar receptors to perceive (E,E)-alpha-farnesene. Our data confirm (E,E)-alpha-farnesene as an alarm pheromone of P. canalifrons.

Nitroalkenes and Sesquiterpene Hydrocarbons from the Frontal Gland of Three Prorhinotermes Termite Species

Frontal gland contents of soldiers of three Prorhinotermes species, Prorhinotermes canalifrons, Prorhinotermes inopinatus, and Prorhinotermes simplex, consisted of two groups of compounds: nitroalkenes and sesquiterpene hydrocarbons. Analysis by gas chromatography-mass spectrometry revealed (E)-1-nitropentadec-1-ene as the major component of the glands with mean values of 152, 207, and 293 microg/individual for P. canalifrons, P. inopinatus, and P. simplex, respectively. Four other 1-nitroalkenes (C13, C14, C16, and C17), and two nitrodienes (C15 and C17) were also detected in the three species. The C17:1 nitroalkene was identified as (E)-1-nitroheptadec-1-ene. The sesquiterpene composition of the gland was species-specific: P. simplex contained (3Z,6E)-alpha-farnesene (mean of 39 microg/individual), while P. canalifrons and P. inopinatus contained the same compound (means of 0.5 and 1.5 microg/individual, respectively) as well as the (3E,6E) isomer (means of 1.8 and 0.7 microg/individual, respectively). Two other sesquiterpenes, trans-beta-bergamotene and (Z)-gamma-bisabolene, were also found in low quantities in the frontal gland of P. canalifrons.

Fungistatic Activity of Freshly Killed Termite,Nasutitermes acajutlae, Soldiers in the Caribbean

Termites may have high exposure to both pathogenic and competitive fungal species. Previous studies have shown anti-fungal properties of the primary components (α-pinene and limonene) of Nasutitermes frontal glands that are present on soldiers. In this study, the termite Nasutitermes acajutlae (Isoptera: Termitidae) was used to examine if the growth of naturally occurring fungi was inhibited by soldiers, as compared to workers that do not have frontal glands. Soldiers and workers were killed, surface sterilized, and placed on nutrient agar either singly or in combinations with other termites. Time until appearance of fungus and growth of visible fungal colonies was determined. Fungus appeared significantly earlier in cultures with single workers than with single soldiers (P < 0.001). Once fungus appeared, there were no significant differences in growth rate. When worker and/or soldier fluids were combined in one culture, fungal growth appeared later in cultures containing soldiers; growth was significantly slower in colonies with 5 workers and 5 soldiers than in cultures with 5 workers alone; P < 0.001. Finally, growth appeared later in cultures with 5 soldiers than in cultures with one soldier, suggesting a dose-response. Fungi that grew from termites were mostly non-pathogenic, suggesting the anti-fungal properties of soldiers may inhibit both pathogens and competitors.

Novel free ceramides as components of the soldier defense gland of the Formosan subterranean termite (Coptotermes formosanus)

Of the lipid extracts of the defense secretion from the Formosan subterranean termite, Coptotermes formosanus Shiraki, on high-performance thin-layer chromatography analysis, no glycolipids or phospholipids were detected, but free fatty acids and three novel ceramides were found (termed TL-1, TL-2, and TL-3). Free fatty acids were confirmed to be lignoceric acid (C24:0) and hexacosanoic acid (C26:0), as described previously [Chen, J., G. Henderson, and R. A. Laine. 1999. Lignoceric acid and hexacosanoic acid: major components of soldier frontal gland secretions of the Formosan subterranean termite (Coptotermes formosanus). J. Chem. Ecol. 25: 817-824]. TL-1, TL-2, and TL-3 were characterized as ceramides differing in hydrophobicity based on results of matrix-assisted laser desorption-ionization time-of-flight mass spectrometry analysis, mild alkaline treatment, GC-MS analysis of fatty acid methylesters, and GC-MS analysis of sphingoid long-chain bases (LCBs) as trimethylsilyl derivatives. Fatty acids in TL-1 and TL-2 were C18:0, C20:0, and C22:0, and those in TL-3 were 2-hydroxy C18:0, C20:0, and C22:0. The most predominant LCB in TL-2 was a novel trihydroxy C(14)-sphingosine, 1,3,9-trihydroxy-2-amino-6-tetradecene. TL-3 contained C(18)-sphinganine and two kinds of novel sphingadienines, 1,3-dihydroxy-2-amino-7,10-hexadecadiene and 1,3-dihydroxy-2-amino-11,14-eicosadiene. Although examination of the biological activities of these novel ceramides was beyond the scope of these studies, because of the minuscule quantities available from termite secretions, it will be interesting in the future to synthesize these molecules for biological testing.

Cloning and expression of a geranylgeranyl diphosphate synthase gene: insights into the synthesis of termite defence secretion

In Nasutitermes takasagoensis, a termite in which soldiers perform specialized chemical defence, Nts19-1 gene is highly expressed exclusively in soldier head. In this study, two types of transcripts for this gene were obtained, and the full-length cDNAs were determined by rapid amplification of cDNA ends (RACE). These transcripts were putative homologues of the geranylgeranyl diphosphate (GGPP) synthase gene, involved in the condensation of dimethylallyl diphosphate with isopentenyl diphosphate in the isoprenoid biosynthetic pathway. The genes were thus termed NtGGPPS1. GGPP is a precursor of diterpenes in plants. In situ hybridization localized NtGGPPS1 expression to the epidermal secretory cells of the frontal gland reservoir where many kinds of diterpenes are produced, suggesting that NtGGPPS1 is involved in the biosynthesis of defence secretion.

Anatomy of the frontal gland and ultramorphology of the frontal tube in the soldier caste of species of Nasutitermitinae (Isoptera, Termitidae)

All termite species (Isoptera) are eusocial. These insects live in societies where the division of labor is a predominant characteristic, conditioned by the presence of castes with different morphology, ontogeny, and development. The soldier caste is unique among social insects and it is responsible for colony defense. Soldiers belonging to the Nasutitermitinae subfamily are very peculiar, since they may be polymorphic and present a nasus in addition to either developed or vestigial mandibles. The defensive secretions of soldiers of the neotropical Nasutitermitinae have been the aim of several chemical studies, but few data exist concerning the anatomy and histology of the exocrine glands. This article presents a comparative study on the anatomy of the frontal gland of soldiers of several Nasutitermitinae species: Syntermes dirus (Burmeister), Syntermes nanus (Constantino), Constrictotermes cyphergaster (Silvestri), Nasutitermes corniger (Motschulsky) and Velocitermes heteropterus (Silvestri), with emphasis on the ultramorphology and ultrastructure of the frontal tube.

The ontogeny of soldiers in Prorhinotermes simplex (Isoptera, Rhinotermitidae)

The ontogeny of the soldier caste in Prorhinotermes simplex is studied with emphasis on the instar origin of soldiers, the duration of the presoldier stage, and changes in external anatomy during the soldier morphogenesis. The soldiers of different instar origin are compared morphometrically and by analysis of the soldier defensive secretion. The soldiers were found to develop from larvae of the second up to the eighth instar, via a short (13–17 days) presoldier stage. The early soldier instars were found exclusively in incipient colonies while the mature colony contains late instar soldiers only. The abrupt change in the external anatomy occurs in two steps. During the larva-presoldier moult, the head increases in length but only slightly in width. During the presoldier-soldier moult, both the length and width of the head increase markedly and the typical cordate shape is attained; the relative size of the pronotum increases considerably. The long falcate mandibles develop mainly during the larva-presoldier moult. One antennal segment is added during these two moults. With increasing instar age of soldiers a relative increase of the pronotum and the head size in its posterior region was observed. No functional differences in external anatomy were found among the six soldier instars. The composition of the frontal gland secretion is similar in the six soldier instars, an extraordinarily high amount of a defensive substance, (E)-1-nitropentadecene, was detected together with (Z,E)-α-farnesene, presumably an alarm substance. The strategy of soldier production is discussed. We conclude that the observed patterns of soldier production in P. simplex correspond well to its ecological strategy of an advanced single-site nester able to migrate and form foraging groups.

Identification of soldier‐specific genes in the nasute termite Nasutitermes takasagoensis (Isoptera: Termitidae)

AbstractIn almost all species of termites (Isoptera), there is a distinct soldier caste that specifically plays a defensive role. In many termite species, soldiers defend the colony mechanically with their mandibles. However, nasute soldiers in the subfamily Nasutitermitinae (family Termitidae) use chemical defense, projecting repellent substances synthesized in frontal glands present within the head. As the nasute soldiers always synthesize a large amount of defensive secretion after soldier differentiation, many genes involved in the biosynthesis of this secretion should always be expressed. To identify and isolate the genes related to chemical defense, we compared the gene expression profiles in the heads of soldiers and workers in a nasute termite, Nasutitermes takasagoensis, by fluorescent differential display (FDD). The ratio of soldier‐specific bands was relatively high (6.9%) compared with that of mandibulate soldiers. The distinct soldier‐specific bands were excised, and 21 sequences of cDNA fragments were cloned. Of these, only seven candidates had homologous sequences to known genes (eukaryotic initiation factor 4A‐I, 3β‐hydroxysteroid dehydrogenase/isomerase family, alkaline phosphatase homolog, GTP‐binding protein, ribosomal protein S13, family 4 cytochrome P450 and an unknown protein). To exclude false positives of the FDD analysis, semi‐quantitative reverse transcription–polymerase chain reaction was carried out for all 21 candidates. Only eight gene candidates (only one showed sequence homology) showed significantly higher expression levels in soldiers than in workers.

Identification of soldier caste-specific protein in the frontal gland of nasute termite Nasutitermes takasagoensis (Isoptera: Termitidae)

The termite soldier is unique because of its defensive task in a colony. In Nasutitermitinae (family Termitidae), soldiers use in their defense frontal glands, which contain various chemical substances. To isolate the gene products related to the chemical defense, we compared the sodium dodecyl sulfate-polyacrylamide gel electrophoresis protein profiles of soldier heads with those of workers of the nasute termite Nasutitermes takasagoensis. We identified a 26-kDa soldier-specific protein (Ntsp1) that exists most abundantly in the dorsal head including the frontal gland. We determined the N-terminal amino acid sequence of Ntsp1, and then cloned the Ntsp1 cDNA by rapid amplification of the cDNA ends-polymerase chain reaction (RACE–PCR). A putative signal peptide was detected upstream of the N-terminus and the Ntsp1 protein showed sequence homologies with known insect secretory carrier proteins, which bind to hydrophobic ligands such as juvenile hormone, suggesting that Ntsp1 belongs to this class of proteins. Northern blot analysis confirmed that the expression level of Ntsp1 was high only in the soldier head. In addition, the localization of Ntsp1 expression was limited in epithelial cells of the frontal gland reservoir, suggesting that this protein binds to some terpenoid(s) preserved in the frontal gland reservoir.

Ultrastructure of the frontal gland in Prorhinotermes simplex (Isoptera: Rhinotermitidae) and quantity of the defensive substance

The frontal gland as a sac-like organ in Prorhinotermes simplex is present only in presoldiers, soldiers, and imagoes, but exists also in nymph-soldier intercastes. The secretory epithelium consists of a single type of secretory cells adhering directly to the cuticular intima. Secretory vacuoles originate in electron dense vesicles, which are transformed into large electron lucent vacuoles. Intermediate vacuoles frequently contain lipid droplets. The frontal gland cells in presoldiers reveal modifications connected with the production of a new cuticle; the new cuticle is thin and compact, whereas the old one is thick, porous, and wrinkled. None of these cuticles is present in soldiers (sic!). In soldiers, the cuticular intima is of endocuticular origin and is formed by dispersed dense material; the apical parts of secretory cells are formed by numerous irregular finger-like projections, true microvilli are completely lacking. In imagoes, the cuticle is composed of an epicuticle, a layer of epicuticular filaments, and one more basal layer; sexual differences were not observed. In nymph-soldier intercastes, the structure of the gland differs in the head and in the metathorax; the head part of the gland resembles the imaginal gland whereas the thoracic part resembles more that of the soldier; the development of secretory vacuoles stops at the stage of presence of lipid droplets. E-1-nitropentadecene was found in the highest amount in soldiers (comparable to P. inopinatus soldiers), in moderate amount in imagoes, and it is missing in both presoldiers and intercastes.

Proximate factors influencing soldier development in the basal termite Cryptotermes secundus (Hill)

Regulation of soldier development in termites at the endocrinological and social scale was intensively studied in the 60s and 70s, but conclusive results are still scanty. In termites, the presence of soldiers inhibits further soldier differentiation, but the mechanism is not well understood. Secretions from the frontal glands seem to be important, but dry- and dampwood termites do not have frontal glands. We investigated the influence of precocene I, a JH-antagonist, and of soldier head extracts on the development of soldiers in the drywood termite, Cryptotermes secundus (Hill). Soldierless colonies produced fewer soldiers when treated with precocene I or soldier head extract than control colonies. Furthermore, colonies treated with precocene I had produced worker-nymph intercastes, last stage nymphs and alates by the end of the experiment (after six months) which were not present in control colonies. Hence, both treatments inhibited soldier development while precocene I simultaneously promoted the development of adult traits, probably by reducing (directly or indirectly) the JH level. The inhibition effect of the soldier head extract indicates that at least in termites without a frontal gland, other sources of material in the head have a regulatory function.

Electron and light microscopic study of various glands and the secretions released into the environment by the turbellarian Urastoma cyprinae.

The turbellarian Urastoma cyprinae (Graff) occurs on the gills of various bivalve species including the mussel Mytilus galloprovinciallis, where it is known to cause serious damage. More recently, it has been shown that the worms are strongly attracted to the gill of the American oyster (Crassostrea virginica) and are capable of inducing changes to the composition of proteolytic enzymes of the host mucus. Such changes may be attributable to secretory products released by the worms. Mucous glands (11-18 mum in diameter) produce minute spherules (0.7-0.9 mum in diameter) tightly bound together. The glands occupy approximately 20% of the body volume and are the most voluminous secretory organs in the worm. The smaller rhabdoid glands are unevenly distributed throughout the peripheral parenchyma and contain secretory granules of 0.35-1.2 mum in diameter. The latter occur most prominently along the distal margins of the epidermis. The frontal pole of U. cyprinae consists of a complex assembly of mucous and rhabdoid gland cells as well as other glandular structures. Collectively, these bodies release their contents to the outside via narrow gland necks. The overall organization is consistent with the frontal gland previously described for other free-living turbellarians, including other rhabdocoels. A variety of secretory products, displaying variations in staining properties, have likewise been identified in association with the body wall from other regions of the worm. This work attempts to gain a better appreciation of the secretory structures associated with the worm tegument, focusing primarily on the widespread mucous and rhabdoid glands. The secretions play a role in host-parasite interactions.

On the anatomy and taxonomy ofTubulanus lutescensn.sp. (Nemertini) from the West Coast of Sweden

Abstract A new species of palaeonemertine from the Swedish west coast, Tubulanus lutescens n. sp., is described and illustrated. The species is characterized by, inter alia, rather well developed cerebral sensory organs, abundant frontal glands and an upper as well as a lower dorsal nerve. There are no lateral sensory organs, excretory organs, rhynchocoel vessels or dorsal and ventral muscle crosses between the outer circular and inner circular body wall muscle layers. The functional morphology of the foregut is discussed.

The frontal weapon of the termite Armitermes euamignathus Silvestri (Isoptera, Termitidae, Nasutitermitinae)

Frontal weapon is the term used to designate the apparatus consisting of frontal gland and associated structures that participate in the chemical defense of termite soldiers. The ultra structure of the frontal gland and the scanning microscopy of the soldier head was investigated in the termite Amiitermes euamignathus Silvestri, 1901.Campaniform sensilla was not observed but there were 80 to100 sensory bristles around the frontal pore. The glandular epithelium shows only class 1 cells according 10 the classification of NOIROT & QUENNEDEY (1974, 1991). The glandular cells are characterized by apical microvilli, a basal labyrinth and a large quantity of smooth endoplasmic reticulum which forms dense zones throughout the cytoplasm. The secretion is concentrated mainly in the basal pole of the cell and consists of large lipid droplets. The secretory epithelium is covered by a thick apical cuticle composed of a thin outer epicuticle, a layer of epicuticular filaments and a dense procuticle. The cytological results concerning the frontal pore showed a reduced cuticle and the presence of a subcuticular space where the lipid droplets are accumulated. The lack of class 3 cells and the presence of an intrinsic musculature are two anatomical features of the A. euamignathus frontal gland that will be important in the phylogenetic relationships of the Nasutitermitinae.

Evidence of tubulin in the scolex gland ducts of Gymnorhynchus gigas plerocercoid (Cestoda: Trypanorhyncha).

Evidence of tubulin in the scolex gland ducts of Gymnorhynchus gigas plerocercoid (Cestoda: Trypanorhyncha).

Tissue-specific expression of an Ornithine decarboxylase paralogue, XODC2, in Xenopus laevis.

Ornithine decarboxylase (ODC) is involved in the biosynthesis of polyamines and hence has been found in almost all types of cells studied. Therefore it is frequently used as internal standard. We isolated a cDNA, XODC2, which is a paralogue to ubiquitous ODC and expressed in a spatial and temporal manner during the early embryogenesis of Xenopus laevis. Expression of XODC2was first detected at the animal pole at stage 9. During neurula stages the signals were found both in the extreme anterior and posterior part of the dorsal body axis. In tailbud stages the expression is further shifted to both the tail and head areas and gradually restricted to distinct tissues: forebrain, inner layer of epidermis of the head area, stomodeal-hypophyseal anlage, frontal gland, ear vesicle, branchial arches, the front tip of neural tube and proctodeum. In addition, signals were also found in the inner layer of epidermis underneath the cement gland during early tailbud stages while in later tailbud stages signals were detected at the apical zone of the cement gland. Comparative studies indeed could confirm that XODC1 in contrast to XODC2 is expressed ubiquitously throughout the whole embryos during early development of Xenopus laevis.