Survey of the exocrine system in Protanilla wallacei (Hymenoptera, Formicidae)

Impact of environmental pollution on ant (Camponotus japonicus) development and labial gland disease

Metallic pollutants can have harmful impacts on ant morphology and physiology. We studied the occurrence of labial gland disease in Camponotus japonicus from two polluted areas (traffic pollution and industrial pollution) and one non-polluted area. We further analyzed the metal levels (Al, As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb and Zn) and morphological characteristics (head width, body mass, and other morphological traits) of both diseased and healthy workers. Our results showed that labial gland disease was only present in polluted areas, indicating that pollution stress makes ants more vulnerable to infections. Our research revealed that diseased ants in polluted areas accumulate higher levels of metals in their bodies and have lower dry weight and residual body mass compared to healthy ants in non-polluted environments, negatively impacting their development. We evaluated the importance of these elements and found that Cu has the greatest impact on the health risk of C. japonicus. Our study underscores the significant impact of environmental pollution on ant morphology and physiology and raises concerns about the broader ecological implications.

Systematic revision of the ant subfamily Leptanillinae (Hymenoptera, Formicidae)

The genus-level taxonomy of the ant subfamily Leptanillinae (Hymenoptera: Formicidae) is here revised, with the aim of delimiting genus-level taxa that are reciprocally monophyletic and readily diagnosable based upon all adult forms. This new classification reflects molecular phylogenetics and is informed by joint consideration of both male and worker morphology. Three valid genera are recognized in the Leptanillinae: Opamyrma, Leptanilla (= Scyphodonsyn. nov., Phaulomyrma, Leptomesites, Noonillasyn. nov., Yavnellasyn. nov.), and Protanilla (= Anomalomyrmasyn. nov., Furcotanilla). Leptanilla and Protanilla are further divided into informal, monophyletic species groups. Synoptic diagnoses are provided for all genera and informal supraspecific groupings. In addition, worker-based keys to all described species within the Leptanillinae for which the worker caste is known are provided; and male-based keys to all species for which males are known, plus undescribed male morphospecies for which molecular data are published. The following species are described as new: Protanillawallaceisp. nov., Leptanillaacherontiasp. nov., Leptanillabelantansp. nov., Leptanillabethyloidessp. nov., and Leptanillanajaphallasp. nov.

The spongiform tissue in Strumigenys ants contains exocrine glands

The insect cuticle is multifunctional and often includes projections used for support, communication or protection. Ants in the genus Strumigenys exhibit a peculiar honeycomb-like spongiform tissue that covers their petiole, postpetiole and sometimes also the posterior mesosoma and anterior part of the first gastral segment. The tissue is abundantly developed in workers and queens, and much reduced in males. We found this spongiform tissue is associated with a novel exocrine gland that is made up by class-3 secretory cells that are clustered underneath the major pillars of the cuticular extensions, their associated narrow ducts enter these extensions and open at the surface through small pores. The chemical nature and function of the secretion are still unknown. The honeycomb texture may act in the storage and dispersion of the glandular secretions. In addition to the spongiform tissue gland, the posterior region of the petiole and postpetiole also contain intersegmental petiole and postpetiole glands, of which the ducts open through the intersegmental membrane that forms the connection with the next segment. Future work aimed at identifying the chemicals secreted by these glands will shed light onto the function of these unusual structures.

Comparative morphology and ultrastructure of the labial gland among castes of Camponotus japonicus (Hymenoptera: Formicidae)

The labial gland is a major exocrine gland in the thoracic cavity of ants, which is connected to the mouth area and opens at the base of the labium. The labial gland in the various castes and males of Camponotus japonicus were examined using dissection, light microscopy, scanning and transmission electron microscopy. Our findings reveal clear caste differences in the appearance of the labial gland, and suggest a relationship between gland structure and its behavioral role in queens, males and workers: queens possess the largest reservoir sac; males have the smallest; workers have abundant secretion droplets in the gland cells of the tubules; epithelial thickness of gland cells varies considerably between workers and reproductive ants. The apical cell region has a high density of microvilli and polymorphic mitochondria, whereas the central cell region is rich in rough endoplasmic reticulum (RER) which means its main secretions are proteinaceous compounds. We believe that the labial gland has a different function in the castes of C. japonicus: the gland of workers and queens may be used to feed the larvae; workers participate in trophallaxis in the nest, while the males are not involved in these activities. Calculations of the relative size of the labial gland for each caste and males indicated that minor workers have the relative highest developed labial gland, supporting a role in trophallaxis. In addition, we found a phenomenon of enlarged labial gland in minor workers, which accounted for almost 22%, but the reason for this is unknown.

Morphology and ultrastructure of the prepharyngeal and pharyngeal glands in the ant Camponotus japonicus

The prepharyngeal gland (prePG) and pharyngeal gland (PG) make up the largest exocrine structures in the head of the ant Camponotus japonicus. We used microscopy to study the histological and ultrastructural features of both glands in different castes. The number of secretory units in the prePG is considerably higher than in other ant species and shows a complex duct system which is made up by duct cells, secondary ducts and a main duct. These lead the secretions of hundreds to thousands of secretory cells into the prepharynx through a modified sieve plate at each side. The glove-shaped PG shows clear caste differences in tubule number. The ultrastructure of both the prePG and PG shows abundant mitochondria and secretion vesicles. Moreover, the prePG is loaded with rough endoplasmic reticulum (RER) which means its main secretions are proteinaceous compounds, while the PG is dominated by smooth endoplasmic reticulum (SER) which means the main secretions are lipids. The morphological differences like cell number of the prePG and tubule number of the PG indicate different secretory abilities of each caste. We for the first time introduce histology-based relative size to indicate secretory activity. The proportionally high development of the prePG in minor workers supports a role in trophallaxis.

Morphology and ultrastructure of the infrabuccal pocket in Strumigenys ants

The morphology of the infrabuccal pocket has been studied with light and electron microscopy (SEM, TEM) in 19 species of Strumigenys ants. The structural organization is similar in workers, queens and males, and supports the involvement of the pocket in the filtration of food particles before they can enter the digestive tract. A carpet of posteriorly oriented bristle hairs on the hypopharynx first guide ingested food into the pocket, where large solid particles are compacted into a pellet that will be regurgitated. The remaining products enter the digestive tract through a filtering wall of parallel hair combs lining the pharynx interior that are directed against the food flow. This mechanical filtering allows only liquids and sufficiently small food particles to enter the digestive system. The wall of the infrabuccal pocket is differentiated into a conspicuous glandular epithelium, of which the ultrastructural characteristics can be understood as an adaptation against the frequent shape changes of the pocket. The gland elaborates a non-proteinaceous secretion, although its functional significance still remains unknown.

Histology and ultrastructure of glands associated with the sting apparatus of the swarm-founding wasp Protopolybia exigua (Hymenoptera: Vespidae: Polistinae)

Social insects present a great diversity of exocrine glands, which are linked to fundamental roles of social life, and their morphological characterization represents the first step toward the knowledge of their function. We here describe the exocrine glands present in the sting apparatus of queens and workers of the wasp Protopolybia exigua. Histological analysis of serial sections under light microscopy revealed a glandular epithelium in the spiracular plate, the quadrate plate, and the gonostyli, while the last two in addition also contain clusters of class-3 cells. A big cluster of class-3 cells was also found in the oblong plate of some workers and queens. These findings reveal that a variety of glands, in addition to the common venom gland and Dufour gland, are present in association with the sting apparatus, of which three glands are novel reports for the exocrine repertoire of social insects. The position of the glands suggests a role in lubrication to provide mobility of the sting and venom ejection and/or participation in alarm behavior, while a function related to reproduction is also possible. The peculiar characteristics displayed by swarm-founding wasps are linked with exocrine gland secretions, making their investigation in Epiponini wasps a vast and interesting field.

The basitarsal sulcus gland, a novel exocrine structure in ants

The basitarsus of the mid- and/or hindlegs of several Amblyoponinae ants shows a deep longitudinal groove or sulcus on its anterior face in workers and queens. Histological examination reveals this sulcus is associated with a conspicuous novel epithelial gland, which brings the number of exocrine glands in the legs of ants to 25. The ultrastructural characteristics of the gland show the presence of a well-developed smooth endoplasmic reticulum. This is indicative for the elaboration of a non-proteinaceous and thus possibly pheromonal secretion. Behavioural observations show that this secretion is collected by the tarsomeres and spread onto the brood and nest, suggesting a role in nestmate recognition. A similar basitarsal sulcus gland was also found in Nothomyrmecia, Paraponera and Tetraponera, which represents both a wide phylogenetic and ecological distribution, as it includes arboreal, ground-dwelling as well as subterranean taxa.

Morphology of the Novel Basimandibular Gland in the Ant Genus Strumigenys (Hymenoptera, Formicidae)

Simple Summary

Ants form a diverse group of social insects that are characterized by an overwhelming variety of exocrine glands, that play a key function in the communication system and social organization of the colony. Our focus goes to the genus Strumigenys, that comprise small slow-moving ants that mainly prey on springtails. We discovered a novel gland inside the mandibles of all 22 investigated species, using light and electron microscopy. As the gland occurs close to the base of the mandibles, we name it ‘basimandibular gland’ according to the putative description given to this mandible region in a publication by the eminent British ant taxonomist Barry Bolton in 1999. The gland exists in both workers and queens and appeared most developed in the queens of Strumigenys mutica. These queens in addition to the basimandibular gland also have a cluster of gland cells near the tip of their mandibles. The queens of this species enter colonies of other Strumigenys species and parasitize on them. We expect that the peculiar development of these glands inside the mandibles of these S. mutica queens plays a role in this parasitic lifestyle, and hope that future research can shed more light on the biology of these ants.

Abstract

In 1999, Barry Bolton postulated the presence of a basimandibular gland in the mandibles in all species of the ant genus Strumigenys, solely based on scanning microscopy observations. We now confirm the presence of this putative gland in the proximal outer part of the mandibles of 22 investigated species by histological and ultrastructural examination, including 10 short- and 12 long-mandibulate species. All species have a basimandibular gland, that is formed by 15–25 µm thick epithelial cells and belongs to class-1 following the standard classification of insect exocrine glands. We consider it a novel gland because of its peculiar bowl-shape and special arrangement of the microvilli that are confined to large vacuolar spaces instead of reaching the cuticle. The gland is most pronounced in S. mutica, particularly in the queen. In addition to this gland, we also found scattered class-3 intramandibular gland cells in the mandibles. Queens of S. mutica are peculiar in having a cluster of these cells in the distal tip of their mandibles. As this species is a social parasite, further research is required to determine whether the development of these mandibular glands is related to its parasitic lifestyle.

Synonymisation of the male-based ant genus Phaulomyrma (Hymenoptera:Formicidae) with Leptanilla based upon Bayesian total-evidence phylogenetic inference

Although molecular data have proven indispensable in confidently resolving the phylogeny of many clades across the tree of life, these data may be inaccessible for certain taxa. The resolution of taxonomy in the ant subfamily Leptanillinae is made problematic by the absence of DNA sequence data for leptanilline taxa that are known only from male specimens, including the monotypic genus Phaulomyrma Wheeler & Wheeler. Focusing upon the considerable diversity of undescribed male leptanilline morphospecies, the phylogeny of 35 putative morphospecies sampled from across the Leptanillinae, plus an outgroup, is inferred from 11 nuclear loci and 41 discrete male morphological characters using a Bayesian total-evidence framework, with Phaulomyrma represented by morphological data only. Based upon the results of this analysis Phaulomyrma is synonymised with Leptanilla Emery, and male-based diagnoses for Leptanilla that are grounded in phylogeny are provided, under both broad and narrow circumscriptions of that genus. This demonstrates the potential utility of a total-evidence approach in inferring the phylogeny of rare extant taxa for which molecular data are unavailable and begins a long-overdue systematic revision of the Leptanillinae that is focused on male material.

Novel exocrine glands in the foreleg coxae of Discothyrea ants

Workers, queens and males of all examined Discothyrea species of the 'sauteri group', that have laterally expanded frontal lobes and well-developed antennal scrobes, are characterized by two hairy areas on the outer surface of their procoxae. Histological and ultrastructural examination of Discothyrea sauterirevealed that each of these areas is associated with a novel exocrine gland: the proximal procoxal gland is formed by a cluster of 15 round secretory cells of 34 μm with numerous mitochondria, smooth endoplasmic reticulum and Golgi apparatus.Their ducts have a diameter of 0.5-1 μm.The distal procoxal gland contains 50 secretory cells of 22 μm with numerous vacuoles and lamellar inclusions, and narrow ducts with a diameter of only 0.15-0.2 μm.The differences in ultrastructural appearance and duct diameter indicate that both glands produce a different but probably pheromonal secretion. The function of these novel procoxal glands could not yet be determined, although observation of D.sauteri workers and queens shows that they make frequent and peculiar leg movements, in which the foreleg basitarsus rubs over the coxal hairy areas. The foreleg basitarsus then rubs the ipsilateral hindleg basitarsus and antenna. As a last step of the sequence, the hindleg basitarsus strokes the gaster.In addition to the occurrence of these novel procoxal glands, histological examination of D. sauteri also revealed the presence of yet another novel but smaller procoxal base gland. Ants of the 'testacea group', that have less developed frontal lobes and no antennal scrobes, do not have procoxal hairy areas, although a distinct sculpturation with small pores may occur in the corresponding areas. The related Proceratium japonicum, that has a similar lifestyle as Discothyrea, does not have any of the procoxal glands and does not display the peculiar leg movements as reported for D. sauteri.

CEH-60/PBX regulates vitellogenesis and cuticle permeability through intestinal interaction with UNC-62/MEIS in Caenorhabditis elegans

The onset of sexual maturity involves dramatic changes in physiology and gene expression in many animals. These include abundant yolk protein production in egg-laying species, an energetically costly process under extensive transcriptional control. Here, we used the model organism Caenorhabditis elegans to provide evidence for the spatiotemporally defined interaction of two evolutionarily conserved transcription factors, CEH-60/PBX and UNC-62/MEIS, acting as a gateway to yolk protein production. Via proteomics, bimolecular fluorescence complementation (BiFC), and biochemical and functional readouts, we show that this interaction occurs in the intestine of animals at the onset of sexual maturity and suffices to support the reproductive program. Our electron micrographs and functional assays provide evidence that intestinal PBX/MEIS cooperation drives another process that depends on lipid mobilization: the formation of an impermeable epicuticle. Without this lipid-rich protective layer, mutant animals are hypersensitive to exogenous oxidative stress and are poor partners for mating. Dedicated communication between the hypodermis and intestine in C. elegans likely supports these physiological outcomes, and we propose a fundamental role for the conserved PBX/MEIS interaction in multicellular signaling networks that rely on lipid homeostasis.

Morphology and ultrastructure of the infrabuccal pocket and its lining epithelium in workers of Ectomomyrmex javanus (Hymenoptera: Formicidae)

This paper describes the morphology and ultrastructure of the infrabuccal pocket in workers of the carnivorous ant Ectomomyrmex javanus, using SEM and TEM. The infrabuccal pocket is a flexible bag with a diameter of 330 ± 30 μm. In its anterior part, the pocket wall reaches a thickness of 24.45 ± 3.45 μm, which is thicker than the wall lining the rest of the infrabuccal pocket, where it measures 6.87 ± 1.12 μm. The epidermal cells of the wall form a thickened epithelium with a thickness of 10.18 ± 2.50 μm. There are different kinds of hairs inside the pocket, that help in filtering solid pellets. Literature data on the infrabuccal pocket are limited and the function of the thicker epithelium is not yet known. It may provide mechanical strength as the pocket undergoes daily size changes because of the filling up and spitting out of pellets.

Novel thoracic glands in the ant Myopias hollandi

Besides the common labial and metapleural glands, four novel exocrine glands are described in the thorax of both workers and queens of the ponerine ant Myopias hollandi. From anterior to posterior, these glands were designated as the propleural pit gland, the posterolateral pronotal gland, the anterolateral propodeal gland and the metasternal process gland. They all correspond with class-3 glands, that are made up of bicellular units that each comprise a secretory cell and a duct cell. In the propleural pit gland, the ducts are characterized by a gradually widening diameter, while in the three other glands the ducts show a portion which displays a balloon-like expansion, that on semithin sections stains very dark. For none of these novel glands the function is known as yet, although ultrastructural examination indicates that they produce a non-proteinaceous and therefore possibly pheromonal secretion.

Morphology and ultrastructure of Dufour's and venom glands in the ant Camponotus japonicus Mayr (Hymenoptera: Formicidae)

The Dufour's and venom glands are two important exocrine glands in ants. In this study, the morphology and fine structure of these two glands are described in the ant Camponotus japonicus Mayr. The Dufour glands have a characteristic bilobed shape and show a difference in size and color between the female castes (minor and major workers, alate and dealate queens). The external surface of Dufour's gland shows different features among the female castes. It appears more hypertrophied in major workers than in the other castes, indicating for a more pronounced function. The cells of the glandular epithelium in Dufour's gland are characterized by abundant mitochondria, basal invaginations and developed muscle fibres. The venom gland is morphologically similar in the different female castes, and consists of a venom reservoir, a convoluted gland and a bifurcated free secretory filament, with the convoluted gland appearing as a large cap lying on top of the reservoir. Cells of the convoluted gland and the free secretory filaments contain numerous mitochondria and a prominent end apparatus. The results will contribute to understanding the functional morphology of these glands among the different castes in Camponotus ants.

Sexual selection and the evolution of male pheromone glands in philanthine wasps (Hymenoptera, Crabronidae)

Background

Sexual selection is thought to promote evolutionary changes and diversification. However, the impact of sexual selection in relation to other selective forces is difficult to evaluate. Male digger wasps of the tribe Philanthini (Hymenoptera, Philanthinae) scent mark territories to attract receptive females. Consequently, the organs for production and storage of the marking secretion, the mandibular gland (MG) and the postpharyngeal gland (PPG), are subject to sexual selection. In female Philanthini, these glands are most likely solely subject to natural selection and show very little morphological diversity. According to the hypothesis that sexual selection drives interspecific diversity, we predicted that the MG and PPG show higher interspecific variation in males than in females. Using histological methods, 3D-reconstructions, and multivariate statistical analysis of morphological characters, we conducted a comparative analysis of the MG and the PPG in males of 30 species of Philanthini and three species of the Cercerini and Aphilanthopsini, two related tribes within the Philanthinae.

Results

We found substantial interspecific diversity in gland morphology with regard to gland incidence, size, shape and the type of associated secretory cells. Overall there was a phylogenetic trend: Ensuing from the large MGs and small PPGs of male Cercerini and Aphilanthopsini, the size and complexity of the MG was reduced in male Philanthini, while their PPG became considerably enlarged, substantially more complex, and associated with an apparently novel type of secretory cells. In some clades of the Philanthini the MG was even lost and entirely replaced by the PPG. However, several species showed reversals of and exceptions from this trend. Head gland morphology was significantly more diverse among male than among female Philanthinae.

Conclusion

Our results show considerable variation in male head glands including the loss of an entire gland system and the evolution of a novel kind of secretory cells, confirming the prediction that interspecific diversity in head gland morphology is higher in male than in female Philanthini. We discuss possible causes for the remarkable evolutionary changes in males and we conclude that this high diversity has been caused by sexual selection.

Electronic supplementary material

The online version of this article (doi:10.1186/s12862-017-0963-6) contains supplementary material, which is available to authorized users.

Pretarsus structure in relation to climbing ability in the ants Brachyponera sennaarensis and Daceton armigerum

We studied the external and internal pretarsus structure of the ants Brachyponera sennaarensis and Daceton armigerum in relation to their very different climbing ability. B. sennaarensis is a ground-dwelling species that is not able to climb vertical smooth walls. They have a pair of straight pretarsal claws with an average claw tip angle of 56 degrees, while the ventral tarsal surface lacks fine hairs that touch the substrate. They have no adhesive pad on the vestigial arolium, while the arolium gland is very small. D. armigerum, on the other hand, is an arboreal and thus well-climbing species with a very strong grip on the substrate. Their pretarsal claws are very hooked, with a claw tip angle around 75 degrees. They have dense arrays of fine hairs on the ventral tarsal surface, a well-developed arolium and arolium gland. These clearly different morphological characteristics are in line with the opposite climbing performance of both species.

Ultrastructure of the mandibular gland of the ant Myrmoteras iriodum

The mandibular gland in workers of the formicine ant Myrmoteras iriodum differs from other ants both in its general morphology and ultrastructural organization. The secretory cells appear in a pseudo-epithelial arrangement that gives them a clear polarity. At their apical side, the cells are characterized by a large cup-like extension of the reservoir, from which a bulbous invagination connects to a branched end apparatus. At the basal side, the cells show a labyrinth of basal invaginations, while the lateral cell contacts show clear interdigitations. The cytoplasmic composition reveals the presence of numerous round or elongate inclusions that contain crystalline material. Microtubules are abundant, and locally fibrillar regions are found. The function of the mandibular gland in M. iriodum has not yet been documented, and should be studied using gland extracts and behavioural observations.

Morphology and ultrastructure of the allomone and sex-pheromone producing mandibular gland of the parasitoid wasp Leptopilina heterotoma (Hymenoptera: Figitidae)

Chemical communication by the parasitoid wasp Leptopilina heterotoma is based largely on (-)-iridomyrmecin. The female wasps use (-)-iridomyrmecin as a defensive allomone, a chemical cue to avoid competition with con- and heterospecific females, and as a major component of their sex pheromone to attract males. Males of L. heterotoma produce (+)-isoiridomyrmecin, which is also used for chemical defense. In this study we show that females and males of L. heterotoma produce the iridomyrmecins in a pair of mandibular glands. Each gland consists of a secretory part composed of class 3 gland cells and their accompanying duct cells, as well as a reservoir bordered by a thin intima. The gland discharges between the mandible base and the clypeus. Males have considerably smaller glands than females, which corresponds to the lower amount of iridomyrmecins produced by males. Chemical analyses of the mandibular gland contents showed that the gland of females contained mainly (-)-iridomyrmecin, as well as low amounts of the other previously described iridoid pheromone compounds, while the glands of males contained only (+)-isoiridomyrmecin. The morphology and sizes of the mandibular glands of males and females of L. heterotoma have evolved to the multi-functional use of iridomyrmecin.

Functional morphology of the maxillary and propharyngeal glands of Monomorium pharaonis (L.)

The maxillary and propharyngeal gland of all 3 castes of Monomorium pharaonis were examined with light and electron microscopy. Although both glands possess a pouch in which secretion can be stored temporarily, a proper reservoir is lacking. The paired maxillary gland opens at the base of the maxilla and consists of 4 secretory cells, which are smaller in workers as compared to queens and males. A digestive role is unlikely as the gland is not directly linked to the digestive system and the amount of rER is negligible. The propharyngeal gland consists of 2 clusters of 16 secretory cells, which open in the pharyngeal atrium through a duct. Secretory cells are smallest in males. Two types of endoplasmic vesicles are observed around the end apparatus, suggesting a release of at least 2 substances. High levels of rER indicate the production of digestive enzymes as one of its functions. No differences between mated versus virgin queens were observed for both glands. Further experiments on chemical and behavioural essays can improve our understanding of the role of both glands in the ant colony. Literature on this topic is very inconsistent. We provide a survey to unravel this chaotic nomenclature issue.

Uncovering head gland diversity in neotropical Polistinae wasps (Hymenoptera, Vespidae): comparative analysis and description of new glands

Exocrine glands are involved in several wasp colony activities; however, the number of known glands in the Vespidae is rather low when compared to other social insect groups. The aim of this study is to survey the head of Neotropical social wasps and to provide a detailed comparative study of the glands found in the Polistinae. A total of 33 species distributed over 13 genera were studied with serial histological sections of the head, excluding the labiomaxillary complex. Additionally, the exoskeleton was explored using scanning electron microscopy looking for associated modifications. A total of eleven exocrine glands were observed, five are structures recorded for the first time for the Hymenoptera, three are new records for the Polistinae and three are previously known organs. The glands studied are: ocellar gland I, ocellar gland II, periocular gland, subantennal gland, hypopharyngeal gland, clypeal gland, posterobasal genal gland, ectal mandibular gland, mesal mandibular gland, intramandibular gland I, and intramandibular gland II. The widespread distribution of most of these glands suggests an origin prior to the evolution of the Polistinae. Our results highlight the importance of detailed morphological studies to unveil the significance of chemical communication in one of the most characteristic groups of social animals.