Ultrastructure of the glands producing sex pheromones of the male Nauphoeta cinerea (Insecta, Dictyoptera)

The ultrastructure of the intramandibular gland in soldiers of the termite Machadotermes rigidus (Blattodea: Termitidae: Apicotermitinae)

Machadotermes is one of the basal Apicotermitinae genera, living in tropical West Africa. Old observations suggested the presence of a new gland, the intramandibular gland, in Machadotermes soldiers. Here, by combining micro-computed tomography, optical and electron microscopy, we showed that the gland exists in Machadotermes soldiers only as an active exocrine organ, consisting of numerous class III cells (bicellular units made of secretory and canal cells), within which the secretion is produced in rough endoplasmic reticulum, and modified and stored in Golgi apparatus. The final secretion is released out from the body through epicuticular canals running through the mandible cuticle to the exterior. We also studied three other Apicotermitinae, Indotermes, Duplidentitermes, and Jugositermes, in which this gland is absent. We speculate that the secretion of this gland may be used as a general protectant or antimicrobial agent. In addition, we observed that the frontal gland, a specific defensive organ in termites, is absent in Machadotermes soldiers while it is tiny in Indotermes soldiers and small in Duplidentitermes and Jugositermes soldiers. At last, we could also observe in all these species the labral, mandibular and labial glands, other exocrine glands present in all termite species studied so far.

Odorous secretions in anurans: morphological and functional assessment of serous glands as a source of volatile compounds in the skin of the treefrog Hypsiboas pulchellus (Amphibia: Anura: Hylidae)

Serous (granular or venom) glands occur in the skin of almost all species of adult amphibians, and are thought to be the source of a great diversity of chemical compounds. Despite recent advances in their chemistry, odorous volatile substances are compounds that have received less attention, and until now no study has attempted to associate histological data with the presence of these molecules in amphibians, or in any other vertebrate. Given the recent identification of 40 different volatile compounds from the skin secretions of H. pulchellus (a treefrog species that releases a strong odour when handled), we examined the structure, ultrastructure, histochemistry, and distribution of skin glands of this species. Histological analysis from six body regions reveals the presence of two types of glands that differ in their distribution. Mucous glands are homogeneously distributed, whereas serous glands are more numerous in the scapular region. Ultrastructural results indicate that electron-translucent vesicles observed within granules of serous glands are similar to those found in volatile-producing glands from insects and also with lipid vesicles from different organisms. Association among lipids and volatiles is also evidenced from chemical results, which indicate that at least some of the volatile components in H. pulchellus probably originate within the metabolism of fatty acids or the mevalonate pathway. As odorous secretions are often considered to be secreted under stress situations, the release of glandular content was assessed after pharmacological treatments, epinephrine administrated in vivo and on skin explants, and through surface electrical stimulation. Serous glands responded to all treatments, generally through an obvious contraction of myoepithelial cells that surround their secretory portion. No response was observed in mucous glands. Considering these morpho-functional results, along with previous identification of volatiles from H. pulchellus and H. riojanus after electrical stimulation, we suggest that the electron-translucent inclusions found within the granules of serous glands likely are the store sites of volatile compounds and/or their precursors. Histochemical and glandular distribution analyses in five other species of frogs of the hylid tribe Cophomantini, revealed a high lipid content in all the species, whereas a heterogeneous distribution of serous glands is only observed in species of the H. pulchellus group. The distribution pattern of serous glands in members of this species group, and the odorous volatile secretions are probably related to defensive functions.

Tarsomere and distal tibial glands: structure and potential roles in termites (Isoptera: Rhinotermitidae, Termitidae)

Social insects have numerous exocrine glands, but these organs are understudied in termites compared to hymenopterans. The tarsomere and distal tibial glands of the termites Heterotermes tenuis, Coptotermes gestroi and Silvestritermes euamignathus were investigated by scanning and transmission electron microscopy. Pore plates are visible in scanning micrographs on the distal tibial surfaces and on the ventral surface of the first and second tarsomeres of workers of H. tenuis and C. gestroi. In contrast, workers of S. euamignathus have isolated pores spread throughout the ventral surfaces of the first, second, and third tarsomeres and the distal tibia. In all three species each pore corresponds to the opening of a class-3 secretory unit, composed of one secretory and one canal cell. Clusters of class-3 glandular cells are arranged side by side underneath the cuticle. The main characteristics of these exocrine glands include their presence on all the legs and the electron-lucent secretion in the secretory cells. Possible functions of these glands are discussed.

The nasus gland: a new gland in soldiers of Angularitermes (Termitidae, Nasutitermitinae)

Termites have developed many exocrine glands, generally dedicated to defence or communication. Although a few of these glands occur in all termite species, or represent synapomorphies of larger clades, others are morphological innovations of a single species, or a few related species. Here, we describe the nasus gland, a new gland occurring at the base of the nasus of Angularitermes soldiers. The nasus gland is composed of class 1, 2, and 3 secretory cells, a rare combination that is only shared by the sternal and tergal glands of some termites and cockroaches. The ultrastructural observations suggest that the secretion is produced by class 2 and 3 secretory cells, and released mostly by class 3 cells. The base of the nasus has a rough appearance due to numerous pits bearing openings of canals conducting the secretion from class 3 secretory cells to the exterior. We tentatively assign a defensive function to the nasus gland, although further research is needed to confirm this function. Although the gland is described only from species of Angularitermes, other genera of Nasutitermitinae also present a rough nasus base, suggesting the presence of a similar, possibly homologous, gland.

The morphogenesis of spermathecae and spermathecal glands in Drosophila melanogaster

Sperm storage in female insects is important for reproductive success and sperm competition. In Drosophila melanogaster females, sperm viability during storage is dependent upon secretions produced by spermathecae and parovaria. Class III dermal glands are present in both structures. Spermathecal glands are initially comprised of a three-cell unit that is refined to a single secretory cell in the adult. It encapsulates an end-apparatus joining to a cuticular duct passing secretions to the spermathecal lumen. We have examined spermatheca morphogenesis using DIC and fluorescence microscopy. In agreement with a recent study, cell division ceases by 36 h after puparium formation (APF). Immunostaining of the plasma membrane at this stage demonstrates that gland cells wrap around the developing end-apparatus and each other. By 48-60 h APF, the secretory cell exhibits characteristic adult morphology of an enlarged nucleus and extracellular reservoir. A novel finding is the presence of an extracellular reservoir in the basal support cell that is continuous with the secretory cell reservoir. Some indication of early spermathecal gland formation is evident in the division of enlarged cells lying adjacent to the spermathecal lumen at 18 h APF and in cellular processes that bind clusters of cells between 24 and 30 h APF.

Tergal glands in termite soldiers of the subfamily Syntermitinae (Isoptera: Termitidae)

The subfamily Syntermitinae comprises 14 genera of termites that are exclusively neotropical. The present study reports morphological data about mandibulate nasute soldiers from termite species belonging to three different genera within this subfamily. We describe tergal glands that were present under all tergites of soldiers of the following species: Cornitermes cumulans, Procornitermes araujoi, Syntermes nanus, and Syntermes wheeleri. The tergal glands were composed of class 2 and class 3 cells. Class 2 cells never reached the cuticle and were located below a flat layer of epidermal cells. Class 3 cells, composed of secretory cells and canal cells, were sporadic, whereas class 2 secretory cells were abundant. Secretory cells of class 3 were narrow and their cytoplasms were filled with several clear, oval-shaped vesicles with limiting membranes. The ultrastructure of class 2 cells showed well-developed smooth endoplasmic reticulum, Golgi apparatus, elongated mitochondria, several electron-lucent vesicles, and electron-dense granules that contain paracrystalline structures in S. nanus. Scanning electron micrographs displayed pores, campaniform sensilla and hairs in the outer cuticle of the soldier tergites. We hypothesize that soldier tergal glands may be involved in the production of defensive compounds, which occur in similar glands of certain cockroaches, or of primer pheromones, that might act in the regulation of soldier differentiation in the termite colony. To date, tergal glands have only been described in termite imagoes, and their occurrence in these soldiers of basal Syntermitinae implies a specific role in this caste that is still speculative and needs to be clarified.

The fine structural organization of sternal glands of pseudergates and workers in termites (Isoptera): a comparative survey

Thirty-nine species belonging to different families of termites are studied to give a comprehensive view of the evolution of the sternal glands. Several modifications occurring at cuticular and cytological levels are described in neuter castes. The outer epicuticle is always pierced by epicuticular pores. In advanced termites the epicuticular filaments greatly increase in number and length creating a thick layer. The pore canals gradually enlarge while the cuticle changes into a lattice structure lining an extracellular space in which the secretion is stored. Two classes of cells are present in basal termites (Mastotermitidae, Hodotermitidae, Termopsidae and Kalotermitidae) but their glandular structures greatly differ between families. A more complex organization with three classes of cells is found in the Serritermitidae and Rhinotermitidae. A regressive evolution occurs in the Termitidae where only two classes of cells are present. A dual nervous control (campaniform sensilla and neurosecretory fibers) is found in lower termites, except for the Hodotermitidae which have mechanosensory bristles. In the other families, neurosecretory fibers are lacking. A comparison with phylogenetic data is given. A more versatile role of sternal glands in neuter castes is hypothesized.

Morphology of the sternal gland in workers of Coptotermes gestroi (Isoptera, Rhinotermitidae)

The sternal gland is considered the only source of trail pheromones in termites. The morphology of the sternal gland was investigated in workers of Coptotermes gestroi using transmission and scanning electron microscopy. The results showed a small bilobed gland at the anterior part of the fifth abdominal sternite. The cuticular surface of the sternal gland showed a V-shaped structure with two peg sensilla in elevated socket and various campaniform sensilla. Pores and cuticular scale-like protuberances also occur in the glandular area. The ultrastructure showed a gland composed of class 1 cells and two different types of class 3 cells distinguished by location, different size and electron-density of secretory vesicles. Small class 3 cells (type 1) of the anterior lobe are inserted among class 1 cells and have weakly electron-dense vesicles associated with mitochondria, glycogen and smooth endoplasmic reticulum. The class 3 cells (type 2) of posterior lobe showed many round electron-lucent vesicles of secretion, abundant free ribosomes and a well-developed Golgi apparatus. Each class 3 cell is connected to the cuticle by a cuticular duct constituted by the receiving canal and the conducting canal. The secretion of class 1 cells is stored in an inner subcuticular reservoir that is delimited by the microvilli of these cells. This inner reservoir is large and crossed by the campaniform sensilla and ducts of two types of class 3 cells that open outside of the insect body. An exterior reservoir also is present between the fourth and fifth sternite. The complex structure of the sternal gland suggests multicomponents for the trail pheromone in the worker of C. gestroi.

The ultrastructure and function of the silk-producing basitarsus in the Hilarini (Diptera: Empididae)

The tribe Hilarini (Diptera: Empididae), commonly known as dance flies, can be recognised by their swollen silk-producing prothoracic basitarsus, a male secondary sexual characteristic. The ultrastructure and function of the silk-producing basitarsus from one undescribed morphospecies of Hilarini, 'Hilarempis 20', is presented. Male H. 20 collect small parcels of diatomaceous algae from the surface of freshwater creeks that they bind with silk produced by the gland in the basitarsus. The gift is then presented to females in a nearby swarm, composed predominately of females. The basitarsus houses approximately 12 pairs of class III dermal glandular units that congregate on the ventral side of the cavity. Each gland cell has a large extracellular lumen where secretion accumulates. The lumen drains to the outside via a conducting canal encompassed by a canal cell and a duct extending through the shaft of a specialised secretory spine. The secretory spines lie in pairs in a ventral groove that runs the length of the basitarsus. A comparison of the basitarsal secretory spines with sensilla on the basitarsi of non gland-bearing legs of males, and with non gland-bearing prothoracic basitarsi of females, suggests that the glandular units are derived from contact chemosensory sensilla.

Characterization of two male-specific polypeptides in the tergal glands secretions of the cockroach Leucophaea maderae (Dictyoptera, Blaberidae)

During the sexual behavior of cockroaches, the female mounts the courting male to feed on the proteinaceous secretion of the tergal glands. Polyacrylamide gel electrophoresis of male and female protein extracts after cuticle wiping revealed three major bands. Two of 18 and 22 kDa, named Lma-P18 and Lma-P22, are specific to the male tergal extracts. Moreover, Lma-P22 is only found in the male second tergite extracts. The third one of 54 kDa, named Lma-P54, is common to male and female extracts and could be considered as an ubiquitous surface protein. Several other minor proteins are also present on the body surface of adults of both sexes. Quantitation of the total protein amount of the male tergal gland secretion shows a progressive accumulation from adult ecdysis to sexual maturity. Western blot analysis using antibodies raised against Lma-P22 and Lma-P54 confirms that Lma-P22 is only secreted by the male second tergite glands. Immunohistolocalization demonstrates that these three major proteins are produced by class 3 glandular cells.