A Phylogenetic Analysis of Ant Morphology (Hymenoptera: Formicidae) with Special Reference to the Poneromorph Subfamilies

Large deformation diffeomorphic mapping of 3D shape variation reveals two distinct mandible and head capsule morphs in Atta vollenweideri leaf-cutter worker ants

Ants are crucial ecosystem engineers, and their ecological success is facilitated by a division of labour among sterile "workers". In some ant lineages, workers have undergone further morphological differentiation, resulting in differences in body size, shape, or both. Distinguishing between changes in size and shape is not trivial. Traditional approaches based on allometry reduce complex 3D shapes into simple linear, areal, or volume metrics; modern approaches using geometric morphometrics typically rely on landmarks, introducing observer bias and a trade-off between effort and accuracy. Here, we use a landmark-free method based on large deformation diffeomorphic metric mapping (LDDMM) to assess the co-variation of size and 3D shape in the mandibles and head capsules of Atta vollenweideri leaf-cutter ants, a species exhibiting extreme worker size-variation. Body mass varied by more than two orders of magnitude, but a shape atlas created via LDDMM on μ-CT-derived 3D mesh files revealed only two distinct head capsule and mandibles shapes-one for the minims (body mass < 1 mg) and one for all other workers. We discuss the functional significance of the identified 3D shape variation, and its implications for the evolution of extreme polymorphism in Atta.

The feeding apparatus of ants: an overview of structure and function

Ants are a dominant family of eusocial terrestrial insects with a diversity of ecologies, lifestyles and morphologies. Ant diet preferences range from strict carnivory through omnivory to almost complete herbivory in species feeding on seeds or exudates of plant-sucking insects. While several studies have investigated ant feeding performance on different substrates, comparatively little is known about the functional morphology of the structures involved in food uptake or their diversification across the ants. To take stock of our current knowledge, we give an overview of how adult ants ingest food, followed by a morphological description of the mouthparts, preoral space and cephalic sucking pump. The mandibles are the most prominent mouthparts and have received considerable attention in the literature, so we focus on the maxillae and labium here. We present current hypotheses for the movement patterns of these parts and discuss morphological differences among ants that may be related to their ecological diversity. Finally, we give short comparisons of the ant condition with some other insects and vertebrates, as well as an outlook summarizing gaps in our knowledge. This sets the stage for future studies elucidating the connections between ant feeding mechanisms and mouthpart evolution. This article is part of the theme issue 'Food processing and nutritional assimilation in animals'.

First discovery of the ant genus Eburopone Borowiec, 2016 (Hymenoptera, Formicidae, Dorylinae) in the Oriental realm, with description of a new species from Vietnam

The doryline ant genus Eburopone Borowiec, 2016 currently contains only one valid species, E.wroughtoni (Forel, 1910) from southern Africa, with a considerable number of undescribed species awaiting formal description in the Afrotropical and Malagasy regions. In the present paper, Eburoponeeasoanasp. nov. is described based on workers and dealate queens from a colony series collected in an evergreen forest on the Dak Lak Plateau of Vietnam (Ea So Nature Reserve, Dak Lak Province). The worker of the new species is morphologically clearly distinguished from E.wroughtoni by the combination of following characteristics: i) frontal line distinct, extending a little beyond mid-length of cranium; ii) anterior (frontoclypeal) margins of torulo-posttorular complex not forming conspicuous lobes protruding over anterior clypeal margin in full-face view; iii) mandibles when closed in full-face view forming only a little space between anterior clypeal margin and mandibles; iv) promesonotal suture faint and inconspicuous; v) abdominal segment III in dorsal view distinctly wider than long, with lateral margins only feebly convex. This represents the first discovery of the genus Eburopone in the Oriental realm, revealing the disjunct distribution of the genus. A partial sequence of the mitochondrial COI gene (658 bp) is provided as a DNA barcode for the new species. A worker-based key to the doryline genera of the Oriental realm is also provided.

A revision of the Cretaceous ant genus Zigrasimecia Barden & Grimaldi, 2013 (Hymenoptera: Formicidae: Zigrasimeciinae)

The extinct Cretaceous ant genus Zigrasimecia Barden & Grimaldi, the iron maiden ants from Myanmar, is revised, and five new species are described: Z. boudinoti sp. nov., Z. caohuijiae sp. nov.,Z. chuyangsui sp. nov., Z. perrichoti sp. nov., and Z. thate sp. nov. Zigrasimecia hoelldobleri paratype (CNU-HYM-MA2019054) is removed from the type series. New diagnoses for all species are provided and species boundaries are discussed. Studied specimens that are not ideally preserved are presented and discussed, some of them are putative new species. Two identification keys for the genus are provided, a traditional, dichotomous key and an interactive, multi-entry key hosted online at the website www.Xper3.fr. I briefly discuss the unlikeliness of the genus Boltonimecia to belong to the subfamily Zigrasimeciinae, and also the taxonomic problem caused by the description of species based on alates and poorly preserved fossils.

Deep time extinction of largest insular ant predators and the first fossil Neoponera (Formicidae: Ponerinae) from Miocene age Dominican amber

BACKGROUND

Ponerine ants are almost exclusively predatory and comprise many of the largest known ant species. Within this clade, the genus Neoponera is among the most conspicuous Neotropical predators. We describe the first fossil member of this lineage: a worker preserved in Miocene-age Dominican amber from Hispaniola.

RESULTS

Neoponera vejestoria sp. nov. demonstrates a clear case of local extinction-there are no known extant Neoponera species in the Greater Antilles. The species is attributable to an extant and well-defined species group in the genus, which suggests the group is older than previously estimated. Through CT scan reconstruction and linear morphometrics, we reconstruct the morphospace of extant and fossil ants to evaluate the history and evolution of predatory taxa in this island system.

CONCLUSIONS

The fossil attests to a shift in insular ecological community structure since the Miocene. The largest predatory taxa have undergone extinction on the island, but their extant relatives persist throughout the Neotropics. Neoponera vejestoria sp. nov. is larger than all other predatory ant workers known from Hispaniola, extant or extinct. Our results empirically demonstrate the loss of a functional niche associated with body size, which is a trait long hypothesized to be related to extinction risk.

Genomic-Phenomic Reciprocal Illumination: Desyopone hereon gen. et sp. nov., an Exceptional Aneuretine-like Fossil Ant from Ethiopian Amber (Hymenoptera: Formicidae: Ponerinae)

Fossils are critical for understanding the evolutionary diversification, turnover, and morphological disparification of extant lineages. While fossils cannot be sequenced, phenome-scale data may be generated using micro-computed tomography (µ-CT), thus revealing hidden structures and internal anatomy, when preserved. Here, we adduce the male caste of a new fossil ant species from Miocene Ethiopian amber that resembles members of the Aneuretinae, matching the operational definition of the subfamily. Through the use of synchrotron radiation for µ-CT, we critically test the aneuretine-identity hypothesis. Our results indicate that the new fossils do not belong to the Aneuretinae, but rather the Ponerini (Ponerinae). Informed by recent phylogenomic studies, we were able to place the fossils close to the extant genus Cryptopone based on logical character analysis, with the two uniquely sharing absence of the subpetiolar process among all ponerine genera. Consequently, we: (1) revise the male-based key to the global ant subfamilies; (2) revise the definitions of Aneuretinae, Ponerinae, Platythyreini, and Ponerini; (3) discuss the evolution of ant mandibles; and (4) describe the fossils as †Desyopone hereon gen. et sp. nov. Our study highlights the value of males for ant systematics and the tremendous potential of phenomic imaging technologies for the study of ant evolution.

First record of Proceratium Roger, 1863, Zasphinctus Wheeler, 1918, and Vollenhovia Mayr, 1865 (Hymenoptera: Formicidae) from the Western Ghats of peninsular India, description of three new species, and implications for Indian biogeography

Three new ant species from the genera Proceratium Roger, 1863, Zasphinctus Wheeler, 1918, and Vollenhovia Mayr, 1865 are described from the Western Ghats of southern India. This is the first report of Proceratium and Zasphinctus from peninsular India and the first record of Vollenhovia from the Western Ghats mountain range proper. Proceratium gibbosum sp. nov. is described from Periyar Tiger Reserve in Kerala, being the first record of the stictum species group from the Indian subcontinent; it differs from other members of the stictum group by the mesonotum bearing a prominent rounded dorsal hump (tumulus) and petiole devoid of ventral tooth. The first record of the genus Zasphinctus Wheeler, 1918 from the Indian region is also presented here, with a description of a new species. Zasphinctus sahyadriensis sp. nov. differs from all known Afrotropical and Asian Zasphinctus by a combination of characters including clypeal area with single median tooth, occipital margin being regular in outline, and head sculpture sparsely punctate. The occurrence of the genus Vollenhovia Mayr, 1865 is confirmed from peninsular India, with the description of the female castes of Vollenhovia keralensis sp. nov. We provide ecological notes on these new taxa. In addition, separate identification keys based on the worker caste are also presented to Indo-Malayan species of Proceratium, Afrotropical-Indomalayan species of Zasphinctus, and Vollenhovia of the Indian subcontinent. The biogeographical implications of the presence of these three genera are also discussed in relation to plate tectonics of the Indian subcontinent.

Ants (Hymenoptera: Formicidae) from Miocene Ethiopian amber: filling gaps in the geological record of African terrestrial biota

The Early Miocene (16–23 Mya) amber of Ethiopia constitutes a new source of fossil ants for Africa, where they are otherwise poorly documented. Here we report a diversified assemblage of six subfamilies and at least 19 genera that are still predominantly alive in the Afrotropics today. In this first account, a particular reference is made to the subfamily Dolichoderinae, with the description of two new species: Technomyrmex svojtkai Perrichot & Engel sp. nov. and Ravavy goldmani Boudinot & Perrichot sp. nov. The first is illustrated and described based on synchrotron-radiation microcomputed tomography, and the second represents the first fossil record for the tribe Bothriomyrmecini and Ravavy, a Malagasy and Afrotropical genus that was hitherto monotypic. The ant composition in Ethiopian amber is congruent with the global pattern emerging across ants and showing a Neogene diversification almost exclusively within extant genera.

Diversity begets diversity: Low resource heterogeneity reduces the diversity of nut-nesting ants in rubber plantations

One of the most general patterns in ecology is the positive relationship between environmental heterogeneity and local diversity. On the one hand, increased resource heterogeneity provides more resources for diverse consumers in the community. On the other hand, increased structural heterogeneity creates variation in the environment's physical structure, thus allowing the coexistence of diverse species with different environmental requirements. Here, we examined the relative importance of resource and structural heterogeneity in determining the taxonomic, functional, and phylogenetic diversity of nut-nesting ants in natural rainforest and rubber plantation. The species richness of nut-nesting ants was 70% higher in rainforest than in rubber plantation. The clustered functional and phylogenetic structure in rubber plantation suggested a strong effect of environmental filtering in shaping ant functional and phylogenetic structure. Nesting heterogeneity (nut diversity) was the major factor explaining variation in taxonomic, functional, and phylogenetic diversity, suggesting that resource heterogeneity plays a major role in shaping the biodiversity patterns of nut-nesting ants. Overall, these results indicate that decreased resource diversity following the conversion of rainforest to rubber plantation can drive biodiversity loss in nut-nesting ants, through its effect on reducing both ant species, functional, and phylogenetic diversity. The decline in species richness and functional and phylogenetic diversity in the local ant community might have major effects on ecosystem functioning.

Distal leg structures of Zoraptera - did the loss of adhesive devices curb the chance of diversification?

The distal leg structures of Zoraptera are documented and discussed with respect to their functional morphology and evolutionary aspects. We investigated eight species using scanning electron microscopy. We analyzed material compositions of the tarsus in three representative species using confocal laser scanning microscopy. When possible, we included both sexes, wing morphs, and nymphs and compared the structures among them. The distal leg structure is unusually uniform across zorapterans regardless of the sex, morphs, and developmental stages. The observed features combine simplification with innovation. The former is likely partially correlated with cryptic microhabitats and miniaturization. Innovation includes a protibial cleaning organ. This is very likely an autapomorphy of Zoraptera. The tarsi are composed of two tarsomeres covered with setae. The pretarsus distally bears an unguitractor plate and well-sclerotized claws. The tarsomeres appear less-sclerotized than the covering setae. The articulation between the basitarsus and tarsomere 2 is hinge-like, implying that tarsomere 2 moves only mediolaterally. The simplified and specialized tarsal morphology is likely suitable for the typical zorapteran microhabitat, under bark. However, the irreversible complete loss of adhesive devices prevented zorapterans to make use of a broader spectrum of environments and was presumably one reason for the species paucity of the group.

3D Volume Rendering of Invertebrates Using Light-Sheet Fluorescence Microscopy

Light-Sheet Fluorescence Microscopy has recently emerged as the technique of choice for obtaining high quality three-dimensional (3D) images of whole organisms, with low photo-damage and fast acquisition rates. Unlike conventional optical and confocal microscopy or scanning electron microscopy systems, it offers the possibility of obtaining multiple views of the sample by rotating it. We show that the use of light-sheet fluorescence microscopy, for the analysis of invertebrates, provides a fair compromise compared to scanning electron microscopy in terms of resolution, but avoids some of its drawbacks, such as sample preparation or limited three-dimensional perspectives. In this paper, we will show how LSFM techniques can provide a cheap, high quality, multicolor, 3D alternative to classic microscopes, for the study of the morphological structure of insects and invertebrates in morphogenesis studies of the whole animal.

Evidence for the evolution of eusociality in stem ants and a systematic revision of †Gerontoformica (Hymenoptera: Formicidae)

It is generally assumed that Cretaceous stem ants were obligately eusocial, because of the presence of wingless adult females, yet the available evidence is ambiguous. Here, we report the syninclusion of a pupa and adult of a stem ant species from Mid-Cretaceous amber. As brood are immobile, the pupa was likely to have been transported by an adult. Therefore, the fossil substantiates the hypothesis that wingless females were cooperators, thus these were true ‘workers’. Re-examination of all described Cretaceous ant species reveals that winged–wingless diphenism – hence a variable dispersal capacity – may have been ancestral to the total clade of the ants, and that highly specialized worker-specific phenotypes evolved in parallel between the stem and crown groups. The soft-tissue preservation of the fossil is exceptional, demonstrating the possibility of analysing the development of the internal anatomy in stem ants. Based on the highest-resolution µ-CT scans of stem ants to date, we describe †Gerontoformica sternorhabda sp. nov., redescribe †G. gracilis, redefine the species group classification of †Gerontoformica, and provide a key to the species of the genus. Our work clarifies the species boundaries of †Gerontoformica and renders fossils relevant to the discussion of eusocial evolution in a way that has heretofore been intractable.

Corrieoponenouragues gen. nov., sp. nov., a new Ponerinae from French Guiana (Hymenoptera, Formicidae)

This study describes the worker and queen castes of the Neotropical ponerine Corrieoponenouraguesgen. nov., sp. nov., an ant from the tropical rainforest in French Guiana. Worker morphology of the taxon is compared with those of other Ponerinae and the similarities between them are discussed, refining the definition of character states for some diagnostic characters at the generic level, providing an identification key to the Neotropical genera, and making some adjustments to the taxonomic framework within the subfamily. Descriptions, diagnosis, character discussion, identification key, and glossary are illustrated with more than 300 images and line drawings. Open science is supported by providing access to measurement data for specimens of the new genus, a matrix of character states for all ponerine taxa evaluated in this study, and specimen data for all examined material. The new or revived combinations presented here are Pachycondylaprocidua Emery, comb. rev., Neoponeracuriosa (Mackay and Mackay), comb. nov., Leptogenysbutteli (Forel), comb. nov., and Bothroponeraescherichi (Forel), comb. nov. In addition, Leptogenysbutteli is synonymized with Leptogenysmyops (Emery), syn. nov.

Shedding Lights on Crude Venom from Solitary Foraging Predatory Ant Ectatomma opaciventre: Initial Toxinological Investigation

Some species of primitive predatory ants, despite living in a colony, exercise their hunting collection strategy individually; their venom is painful, paralyzing, digestive, and lethal for their prey, yet the toxins responsible for these effects are poorly known. Ectatomma opaciventre is a previously unrecorded solitary hunting ant from the Brazilian Cerrado. To overcome this hindrance, the present study performed the in vitro enzymatic, biochemical, and biological activities of E. opaciventre to better understand the properties of this venom. Its venom showed several proteins with masses ranging from 1-116 kDa, highlighting the complexity of this venom. Compounds with high enzymatic activity were described, elucidating different enzyme classes present in the venom, with the presence of the first L-amino acid oxidase in Hymenoptera venoms being reported. Its crude venom contributes to a state of blood incoagulability, acting on primary hemostasis, inhibiting collagen-induced platelet aggregation, and operating on the fibrinolysis of loose red clots. Furthermore, the E. opaciventre venom preferentially induced cytotoxic effects on lung cancer cell lines and three different species of Leishmania. These data shed a comprehensive portrait of enzymatic components, biochemical and biological effects in vitro, opening perspectives for bio-pharmacological application of E. opaciventre venom molecules.

Anatomy and evolution of the head of Dorylus helvolus (Formicidae: Dorylinae): Patterns of sex- and caste-limited traits in the sausagefly and the driver ant

Ants are highly polyphenic Hymenoptera, with at least three distinct adult forms in the vast majority of species. Their sexual dimorphism, however, is overlooked to the point of being a nearly forgotten phenomenon. Using a multimodal approach, we interrogate the near total head microanatomy of the male of Dorylus helvolus, the "sausagefly," and compare it with the conspecific or near-conspecific female castes, the "driver ants." We found that no specific features were shared uniquely between the workers and males to the exclusion of the queens, indicating independence of male and worker development; males and queens, however, uniquely shared several features. Certain previous generalizations about ant sexual dimorphism are confirmed, while we also discover discrete muscular presences and absences, for which reason we provide a coarse characterization of functional morphology. Based on the unexpected retention of a medial carinate line on the structurally simplified mandible of the male, we postulate a series of developmental processes to explain the patterning of ant mandibles. We invoke functional and anatomical principles to classify sensilla. Critically, we observe an inversion of the expected pattern of male-queen mandible development: male Dorylus mandibles are extremely large while queen mandibles are poorly developed. To explain this, we posit that the reproductive-limited mandible phenotype is canalized in Dorylus, thus partially decoupling the queen and worker castes. We discuss alternative hypotheses and provide further comparisons to understand mandibular evolution in army ants. Furthermore, we hypothesize that the expression of the falcate phenotype in the queen is coincidental, that is, a "spandrel," and that the form of male mandibles is also generally coincidental across the ants. We conclude that the theory of ant development and evolution is incomplete without consideration of the male system, and we call for focused study of male anatomy and morphogenesis, and of trait limitation across all castes.

Morphology and closing mechanism of the mandibular gland orifice in ants (Hymenoptera: Formicidae)

The mandibular gland of ants releases chemical compounds with functions ranging from nestmate alarm and recognition to antimicrobial defense. While the morphology of this ethologically important gland is well investigated in several species, the mechanism of secretion release in ants was not explicitly addressed so far. To clarify this question, we examined the anatomy of the gland orifice in ant species from 14 different subfamilies employing different techniques. The orifice close to the mandibular base is located on an area called mandalus. Our investigations revealed variation in mandalar shape, with clear trends in different subfamilies. By contrast, the internal organization is remarkably congruent across all investigated species. The thin external mandalar cuticle is always connected to the mandibular gland duct by a cuticular lamella, visible as a characteristic anchor-shaped structure in cross section. The slit-like gland orifice at the distal end of the mandalus is usually crescent-shaped. In some ant species with specialized mandibles such as trap-jaws, the organization of the orifice area is adapted to the mandibular shape, but always retains the general internal organization. No muscles were found in association with the orifice, nor with any other part of the mandibular gland. However, the base of the mandalus is connected to the prepharyngeal sucking pump by a cuticular ligament. Additionally, it is continuous with the conjunctiva connecting the mandible to the head capsule. We propose that retraction of the sucking pump by the muscle M. tentoriobuccalis, potentially in concert with opening of the mandible, stretches out the ligament and thus pulls on the mandalus and mandalar lamella to open the gland orifice and allow for secretion release. This hypothesis is congruent with findings on other aculeate Hymenoptera and expands our knowledge on the function of an important gland of ants.

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.

† Camelosphecia gen. nov., lost ant-wasp intermediates from the mid-Cretaceous (Hymenoptera, Formicoidea)

Fossils provide primary material evidence for the pattern and timing of evolution. The newly discovered "beast ants" from mid-Cretaceous Burmite, †Camelosphecia gen. nov., display an exceptional combination of plesiomorphies, including absence of the metapleural gland, and a series of unique apomorphies. Females and males, represented by †C. fossor sp. nov. and †C. venator sp. nov., differ in a number of features which suggest distinct sexual biologies. Combined-evidence phylogenetic analysis recovers †Camelosphecia and †Camelomecia as a clade which forms the extinct sister group of the Formicidae. Notably, these genera are only known from alate males and females; workers, if present, have yet to be recovered. Based on ongoing study of the total Aculeata informed by the beast ant genera, we provide a brief diagnosis of the Formicoidea. We also provide the first comprehensive key to the major groupings of Mesozoic Formicoidea, alongside a synoptic classification in which †Zigrasimeciinaestat. nov. and †Myanmyrma maraudera comb. nov. are recognized. Finally, a brief diagnosis of the Formicoidea is outlined.

Evidence for a thoracic crop in the workers of some Neotropical Pheidole species (Formicidae: Myrmicinae)

The ability of ant colonies to transport, store, and distribute food resources through trophallaxis is a key advantage of social life. Nonetheless, how the structure of the digestive system has adapted across the ant phylogeny to facilitate these abilities is still not well understood. The crop and proventriculus, structures in the ant foregut (stomodeum), have received most attention for their roles in trophallaxis. However, potential roles of the esophagus have not been as well studied. Here, we report for the first time the presence of an auxiliary thoracic crop in Pheidole aberrans and Pheidole deima using X-ray micro-computed tomography and 3D segmentation. Additionally, we describe morphological modifications involving the endo- and exoskeleton that are associated with the presence of the thoracic crop. Our results indicate that the presence of a thoracic crop in major workers suggests their potential role as repletes or live food reservoirs, expanding the possibilities of tasks assumed by these individuals in the colony. Our contribution emphasizes the utility of combining data from external and internal morphology to better understand functional and behavioral mechanisms.

Specialized Predation Drives Aberrant Morphological Integration and Diversity in the Earliest Ants

Extinct haidomyrmecine "hell ants" are among the earliest ants known [1, 2]. These eusocial Cretaceous taxa diverged from extant lineages prior to the most recent common ancestor of all living ants [3] and possessed bizarre scythe-like mouthparts along with a striking array of horn-like cephalic projections [4-6]. Despite the morphological breadth of the fifteen thousand known extant ant species, phenotypic syndromes found in the Cretaceous are without parallel and the evolutionary drivers of extinct diversity are unknown. Here, we provide a mechanistic explanation for aberrant hell ant morphology through phylogenetic reconstruction and comparative methods, as well as a newly reported specimen. We report a remarkable instance of fossilized predation that provides direct evidence for the function of dorsoventrally expanded mandibles and elaborate horns. Our findings confirm the hypothesis that hell ants captured other arthropods between mandible and horn in a manner that could only be achieved by articulating their mouthparts in an axial plane perpendicular to that of modern ants. We demonstrate that the head capsule and mandibles of haidomyrmecines are uniquely integrated as a consequence of this predatory mode and covary across species while finding no evidence of such modular integration in extant ant groups. We suggest that hell ant cephalic integration-analogous to the vertebrate skull-triggered a pathway for an ancient adaptive radiation and expansion into morphospace unoccupied by any living taxon.

Odontomachus davidsoni sp. nov. (Hymenoptera, Formicidae), a new conspicuous trap-jaw ant from Ecuador

One of the largest species in its genus, Odontomachusdavidsoni Hoenle, Lattke & Donoso, sp. nov. is described from workers and queens collected at lowland forests in the Chocó-Darién bioregion in coastal Ecuador. The workers are characterized by their uniform red coloration, their large size (16–18 mm body length), and their frontal head striation that reaches the occipital margin. DNA barcodes (COI) and high resolution 2D images of the type material are provided, as well as an updated key for the Neotropical species of Odontomachus. In addition, a three-dimensional digital model of the worker holotype and a paratype queen scanned with DISC3D based on photogrammetry is presented, for the first time in a species description. Findings of large and conspicuous new species are uncommon around the world and suggest that these Ecuadorian rainforests may conceal many more natural treasures that deserve conservation.

Distal leg structures of the Aculeata (Hymenoptera): A comparative evolutionary study of Sceliphron (Sphecidae) and Formica (Formicidae)

The distal parts of the legs of Sceliphron caementarium (Sphecidae) and Formica rufa (Formicidae) are documented and discussed with respect to phylogenetic and functional aspects. The prolegs of Hymenoptera offer an array of evolutionary novelties, mainly linked with two functional syndromes, walking efficiently on different substrates and cleaning the body surface. The protibial-probasitarsomeral cleaning device is almost always well-developed. A complex evolutionary innovation is a triple set of tarsal and pretarsal attachment devices, including tarsal plantulae, probasitarsomeral spatulate setae, and an arolium with an internal spring-like arcus, a dorsal manubrium, and a ventral planta. The probasitarsal adhesive sole and a complex arolium are almost always preserved, whereas the plantulae are often missing. Sceliphron has retained most hymenopteran ground plan features of the legs, and also Formica, even though the adhesive apparatus of Formicidae shows some modifications, likely linked to ground-oriented habits of most ants. Plantulae are always absent in extant ants, and the arolium is often reduced in size, and sometimes vestigial. The arolium contains resilin in both examined species. Additionally, resilin enriched regions are also present in the antenna cleaners of both species, although they differ in which of the involved structures is more flexible, the calcar in Sceliphron and the basitarsal comb in Formica. Functionally, the hymenopteran distal leg combines (a) interlocking mechanisms (claws, spine-like setae) and (b) adhesion mechanisms (plantulae, arolium). On rough substrate, claws and spine-like setae interlock with asperities and secure a firm grip, whereas the unfolding arolium generates adhesive contact on smooth surfaces. Differences of the folded arolium of Sceliphron and Formica probably correlate with differences in the mechanism of folding/unfolding.

Maritime trap-jaw ants (Hymenoptera, Formicidae, Ponerinae) of the Indo-Australian region - redescription of Odontomachus malignus Smith and description of a related new species from Singapore, including first descriptions of males

The maritime trap-jaw ant Odontomachusmalignus Smith, 1859 is thought to be widespread throughout islands in the Indo-Pacific and parts of the Oriental realm. Because of its unique nesting preference for harsh littoral habitat and distinct morphology, O.malignus has usually been assumed to consist of only one species. We, however, describe a new species similar to O.malignus found in the mangroves of Singapore, Southeast Asia – Odontomachuslitoralissp. nov. We find strong evidence of both species existing in (near) sympatry, and also distinct morphological differences between O.malignus and the new species. Additional complementary DNA evidence in the form of COI barcodes (313 bp) supporting putative species identification and delimitation is provided. Defining morphological characteristics for the O.malignus species group (nested within the larger O.infandus clade) are given in detail for the first time. The worker and queen castes of the new species are described; a redescription of the worker caste of O.malignus, based on specimens from Singapore and the Philippines in addition to the holotype, is also given. The males of both species are also described for the first time, including male genitalia. A preliminary key to most known species of the O.infandus group based on the worker caste is provided.

Using controlled vocabularies in anatomical terminology: A case study with Strumigenys (Hymenoptera: Formicidae)

Morphological studies of insects can help us to understand the concomitant or sequential functionality of complex structures and may be used to hypothetize distinct levels of phylogenetic relationship among groups. Traditional morphological works, generally, have encompassed a set of elements, including descriptions of structures and their respective conditions, literature references and images, all combined in a single document. Fast forward to the digital era, it is now possible to release this information simultaneously but also independently as data sets linked to the original publication in an external environment. In order to link data from various fields of knowledge, disseminating morphological information in an open environment, it is important to use tools that enhance interoperability. For example, semantic annotations facilitate the dissemination and retrieval of phenotypic data in digital environments. The integration of semantic (i.e. web-based) components with anatomic treatments can be used to generate a traditional description in natural language along with a set of semantic annotations. The ant genus Strumigenys currently comprises about 840 described species distributed worldwide. In the Neotropical region, almost 200 species are currently known, but it is possible that much of the species' diversity there remains unexplored and undescribed. The morphological diversity in the genus is high, reflecting an extreme generic reclassification that occurred in the late 20th and early 21st centuries. Here we define the anatomical concepts in this highly diverse group of ants using semantic annotations to enrich the anatomical ontologies available online, focussing on the definition of terms through subjacent conceptualization.

A new species and new record of the cryptobiotic ant genus Ponera Latreille, 1804 (Hymenoptera, Formicidae) from Hong Kong

Despite its small size, Hong Kong hosts a surprising level of ant diversity. Through faunal studies on arthropods conducted in Hong Kong over recent years, a new record and species of the genus Ponera have been discovered, which are introduced here. Ponera guangxiensis Zhou, 2001 is reported for the first time from Hong Kong, and Ponera tudigong sp. nov. is here described as a new species, easily distinguishable from other Ponera species and unique within the genus for its four mandibular teeth.

The cephalic anatomy of workers of the ant species Wasmannia affinis (Formicidae, Hymenoptera, Insecta) and its evolutionary implications

Despite the ecological significance of ants and the intensive research attention they have received, thorough treatments of the anatomy and functional morphology are still scarce. In this study we document the head morphology of workers of the myrmicine Wasmannia affinis with optical microscopy, μ-computed tomography, scanning electron microscopy, and 3D reconstruction, providing the first complete anatomical treatment of an ant head with a broad array of modern techniques. We discuss the potential of the applied methods to generate detailed and well-documented morphological data sets with increased efficiency. We also address homology problems, particularly in the context of the cephalic digestive tract. According to our analyses the "pharynx" of previous ant studies is homologous to the prepharynx of other insects. We also discuss the phylogenetic potential and functional significance of the observed characters, with internal features such as tentorium and musculature discussed for the first time. Our investigation underlines that detailed anatomical data for Formicidae are still very fragmentary, which in turn limits our understanding of the major design elements underlying the ant bauplan. We attempt to provide a template for further anatomical studies, which will help to understand the evolution of this fascinating group on the phenotypic level.

A new species of Boloponera from Sekhukhuneland, South Africa (Hymenoptera, Formicidae, Ponerinae)

During an environmental impact assessment survey of a proposed tailings storage facility for a platinum mine in Sekhukhuneland, South Africa, five adult and five larval specimens of a new species of Boloponera were found while excavating soil to a depth of 10–15 cm at the base of a tree in riparian woodland. These specimens represent a 3400 km range extension and the first reported record of the genus since its description in 2006, which was based on a single specimen collected in the Central African Republic in 2001. A description of the worker and ergatoid queen of Boloponeraikemkhasp. n. is presented, with a description of the mature larva and a key to distinguish workers of the two currently known species of the genus. The taxonomic relationships of Boloponera are discussed with respect to several confirmed and newly identified autapomorphies that support its retention as a distinct genus, although closely related to Plectroctena and Loboponera. A preliminary assessment of the conservation status and discussion of potential threats to the survival of B.ikemkha is also provided. Evaluation of current data under the IUCN Red List criteria would result in B.ikemkha being assessed as Critically Endangered, but further investigation is required to test the validity of placing it in this category.

A new species of Stigmatomma from Taiwan (Hymenoptera, Formicidae, Amblyoponinae)

Stigmatomma is the most speciose ant genus in the subfamily Amblyoponinae. In the present paper, the worker caste of a new species is described, S.luyiaesp. n., which was collected from a soil sample in a subtropical evergreen broad-leaved forest in Taiwan. An identification key to the females of Stigmatomma species with 11 antennomeres occurring in Asia is also provided.

Taxonomic overview of the hyperdiverse ant genus Tetramorium Mayr (Hymenoptera, Formicidae) in India with descriptions and X-ray microtomography of two new species from the Andaman Islands

With 600 described species, the ant genus Tetramorium represents one of the most species-rich ant radiations. However, much work remains to fully document the hyperdiversity of this remarkable group. Tetramorium, while globally distributed, is thought to have originated in the Afrotropics and is particularly diverse in the Old World. Here, we focus attention on the Tetramorium fauna of India, a region of high biodiversity value and interest for conservation. We overview Tetramorium diversity in India by providing a species list, accounts of all species groups present, an illustrated identification key to Indian Tetramorium species groups and notes on the Indian Tetramorium fauna. Further, we describe two new species, Tetramorium krishnani sp. n. and Tetramorium jarawa sp. n. from the Andaman Islands archipelago and embed them into currently recognized Tetramorium tonganum and Tetramorium inglebyi species groups. We also provide illustrated species level keys for these groups. Along with detailed species descriptions and high-resolution montage images of types, we provide 3D cybertypes of the new species derived from X-ray micro-computed tomography.

Next-generation morphological character discovery and evaluation: an X-ray micro-CT enhanced revision of the ant genus Zasphinctus Wheeler (Hymenoptera, Formicidae, Dorylinae) in the Afrotropics

New technologies for imaging and analysis of morphological characters offer opportunities to enhance revisionary taxonomy and better integrate it with the rest of biology. In this study, we revise the Afrotropical fauna of the ant genus Zasphinctus Wheeler, and use high-resolution X-ray microtomography (micro-CT) to analyse a number of morphological characters of taxonomic and biological interest. We recognise and describe three new species: Z. obamaisp. n., Z. sarowiwaisp. n., and Z. wilsonisp. n. The species delimitations are based on the morphological examination of all physical specimens in combination with 3D scans and volume reconstructions. Based on this approach, we present a new taxonomic discrimination system for the regional fauna that consists of a combination of easily observable morphological characters visible at magnifications of around 80-100 ×, less observable characters that require higher magnifications, as well as characters made visible through virtual dissections that would otherwise require destructive treatment. Zasphinctus are rarely collected ants and the material available to us is comparatively scarce. Consequently, we explore the use of micro-CT as a non-invasive tool for the virtual examination, manipulation, and dissection of such rare material. Furthermore, we delineate the treated species by providing a diagnostic character matrix illustrated by numerous images and supplement that with additional evidence in the form of stacked montage images, 3D PDFs and 3D rotation videos of scans of major body parts and full body (in total we provide 16 stacked montage photographs, 116 images of 3D reconstructions, 15 3D rotation videos, and 13 3D PDFs). In addition to the comparative morphology analyses used for species delimitations, we also apply micro-CT data to examine certain traits, such as mouthparts, cuticle thickness, and thoracic and abdominal muscles in order to assess their taxonomic usefulness or gain insights into the natural history of the genus. The complete datasets comprising the raw micro-CT data, 3D PDFs, 3D rotation videos, still images of 3D models, and coloured montage photos have been made available online as cybertypes (Dryad, http://dx.doi.org/10.5061/dryad.4s3v1).

Generic revision of the ant subfamily Dorylinae (Hymenoptera, Formicidae)

The generic classification of the ant subfamily Dorylinae is revised, with the aim of facilitating identification of easily-diagnosable monophyletic genera. The new classification is based on recent molecular phylogenetic evidence and a critical reappraisal of doryline morphology. New keys and diagnoses based on workers and males are provided, along with reviews of natural history and phylogenetic relationships, distribution maps, and a list of valid species for each lineage. Twenty-eight genera (27 extant and 1 extinct) are recognized within the subfamily, an increase from 20 in the previous classification scheme. Species classified in the polyphyletic Cerapachys and Sphinctomyrmex prior to this publication are here distributed among 9 and 3 different genera, respectively. Amyrmex and Asphinctanilloides are synonymized under Leptanilloides and the currently recognized subgenera are synonymized for Dorylus. No tribal classification is proposed for the subfamily, but several apparently monophyletic genus-groups are discussed. Valid generic names recognized here include: Acanthostichus (= Ctenopyga), Aenictogiton, Aenictus (= Paraenictus, Typhlatta), Cerapachys (= Ceratopachys), Cheliomyrmex, Chrysapace gen. rev., Cylindromyrmex (= Holcoponera, Hypocylindromyrmex, Metacylindromyrmex), Dorylus (= Alaopone syn. n., Anomma syn. n., Cosmaecetes, Dichthadia syn. n., Rhogmus syn. n., Shuckardia, Sphecomyrmex, Sphegomyrmex, Typhlopone syn. n.), Eburopone gen. n., Eciton (= Camptognatha, Holopone, Mayromyrmex), Eusphinctus gen. rev., Labidus (= Nycteresia, Pseudodichthadia), Leptanilloides (= Amyrmex syn. n., Asphinctanilloides syn. n.), Lioponera gen. rev. (= Neophyracaces syn. n., Phyracaces syn. n.), Lividopone, Neivamyrmex (= Acamatus, Woitkowskia), Neocerapachys gen. n., Nomamyrmex, Ooceraea gen. rev. (= Cysias syn. n.), Parasyscia gen. rev., †Procerapachys, Simopone, Sphinctomyrmex, Syscia gen. rev., Tanipone, Vicinopone, Yunodorylus gen. rev., Zasphinctus gen. rev. (= Aethiopopone syn. n., Nothosphinctus syn. n.).

Taxonomic revision of Stigmatomma Roger (Hymenoptera: Formicidae) in the Malagasy region

In this study we present the first taxonomic revision of the ant genus Stigmatomma in the Malagasy biogeographic region, re-describe the previously known S. besucheti Baroni-Urbani, and describe seven new species to science (S. bolabola sp. n., S. irayhady sp. n., S. janovitsika sp. n., S. liebe sp. n., S. roahady sp. n., S. sakalava sp. n., and S. tsyhady sp. n.). The revision is based on the worker caste, but we provide brief descriptions of gynes and males for some species. Species descriptions, diagnosis, character discussion, identification key, and glossary are illustrated with 360 high-quality montage and SEM images. The distribution of Stigmatomma species in Madagascar are mapped and discussed within the context of the island's biomes and ecoregions. We also discuss how some morphometric variables describe the differences among the species in the bioregion. Open science is supported by providing access to R scripts, raw measurement data, and all specimen data used. All specimens used in this study were given unique identifies, and holotypes were imaged. Specimens and images are made accessible on AntWeb.org.

Five new species of entomopathogenic fungi from the Amazon and evolution of neotropical Ophiocordyceps

The neotropical biogeographic zone is a 'hot spot' of global biodiversity, especially for insects. Fungal pathogens of insects appear to track this diversity. However, the integration of this unique component of fungal diversity into molecular phylogenetic analyses remains sparse. The entomopathogenic fungal genus Ophiocordyceps is species rich in this region with the first descriptions dating to the early nineteenth century. In this study, material from various ecosystems throughout Colombia and Ecuador was examined. Molecular phylogenetic analyses of five nuclear loci including SSU, LSU, TEF, RPB1, and RPB2 were conducted alongside a morphological evaluation. Thirty-five specimens were examined representing fifteen different species of Ophiocordyceps, and five new species, Ophiocordyceps blattarioides, Ophiocordyceps tiputini, Ophiocordyceps araracuarensis, Ophiocordyceps fulgoromorphila, and Ophiocordyceps evansii, were described. An accurate identification of the host allowed us to conclude that host identity and host habitat are positively correlated with phylogenetic species of Ophiocordyceps and are probably strong drivers for speciation of neotropical entomopathogenic fungi.

Revision of the ant genus Proceratium Roger (Hymenoptera, Proceratiinae) in Fiji

The Fiji archipelago harbours a surprisingly diverse and endemic ant fauna, despite its isolated and remote location in the South Pacific. The ant genus Proceratium is present on Fiji with three endemic species, of which Proceratiumoceanicum De Andrade, 2003 and Proceratiumrelictum Mann, 1921 were previously known. In this study we describe the third species: Proceratiumvinakasp. n. All three species are members of the widespread and species-rich Proceratiumsilaceum clade. In order to integrate the new species into the current taxonomic system, we present an illustrated identification key to the worker caste of the three Fijian species. In addition, we provide a detailed description of Proceratiumvinaka, as well as species accounts for the other two species, which include diagnoses, taxonomic discussions, specimen photographs, and a distribution map.

Taxonomy of the ant genus Proceratium Roger (Hymenoptera, Formicidae) in the Afrotropical region with a revision of the P.arnoldi clade and description of four new species

The taxonomy of the genus Proceratium Roger is updated for the Afrotropical region. We give an overview of the genus in the region, provide an illustrated identification key to the three clades (Proceratiumarnoldi, Proceratiumstictum and Proceratiumtoschii clades) and revise the Proceratiumarnoldi clade. Four new species from the Proceratiumarnoldi clade are described as new: Proceratiumsokoke sp. n. from Kenya, Proceratiumcarri sp. n. from Mozambique, and Proceratiumnilo sp. n. and Proceratiumsali sp. n. from Tanzania. In order to integrate the new species into the existing taxonomic system we present an illustrated identification key to distinguish the seven Afrotropical species of the Proceratiumarnoldi clade. In addition, we provide accounts for all members of the Proceratiumarnoldi clade including detailed descriptions, diagnoses, taxonomic discussions, distribution data and high quality montage images.

A revision of the ant genus Mystrium in the Malagasy region with description of six new species and remarks on Amblyopone and Stigmatomma (Hymenoptera, Formicidae, Amblyoponinae)

The genus Mystrium is revised for the Malagasy region. Six species, Mystrium barrybresslerisp. n., Mystrium labyrinthsp. n., Mystrium equessp. n., Mystrium mirrorsp. n., Mystrium shadowsp. n., and Mystrium janovitzisp. n. are described as new. Two existing names, Mystrium fallax Forel and Mystrium stadelmanni Forel, are synonymized with Mystrium voeltzkowi Forel and Mystrium mysticum Roger, respectively. All recognized species, including species outside of the Malagasy region, are assigned to one of the three newly proposed species groups. The associations between existing names and males are reexamined, and males of eight of the ten Malagasy species are described or redescribed. The taxonomic history of Mystrium highlights the importance of using unique identifiers when designating type specimens and the use of deposited vouchers in phylogenetic and ecological studies. Keys to species for workers, queens, and males are provided. Furthermore, a neotype for Mystrium mysticum is designated, as well as lectotypes for Mystrium camillae Emery, Mystrium rogeri Forel, Mystrium fallax Forel, Mystrium oberthueri Forel, Mystrium stadelmanni Forel, and Mystrium voeltzkowi Forel. Stigmatomma gingivale (Brown) is reassigned to Amblyopone as comb. rev. and Amblyopone awa Xu & Chu, Amblyopone kangba Xu & Chu, Amblyopone meiliana Xu & Chu, and Amblyopone zomae Xu & Chu are transferred to the genus Stigmatomma as comb. n.

Evolution of thorax architecture in ant castes highlights trade-off between flight and ground behaviors

The concerted evolution of morphological and behavioral specializations has compelling examples in ant castes. Unique to ants is a marked divergence between winged queens and wingless workers, but morphological specializations for behaviors on the ground have been overlooked. We analyzed thorax morphology of queens and workers in species from 21 of the 25 ant subfamilies. We uncovered unique skeletomuscular modifications in workers that presumably increase power and flexibility of head-thorax articulation, emphasizing that workers are not simply wingless versions of queens. We also identified two distinct types of queens and showed repeated evolutionary associations with strategies of colony foundation. Solitary founding queens that hunt have a more worker-like thorax. Our results reveal that ants invest in the relative size of thorax segments according to their tasks. Versatility of head movements allows for better manipulation of food and objects, which arguably contributed to the ants' ecological and evolutionary success. DOI: http://dx.doi.org/10.7554/eLife.01539.001.

Ants and the fossil record

The dominance of ants in the terrestrial biosphere has few equals among animals today, but this was not always the case. The oldest ants appear in the fossil record 100 million years ago, but given the scarcity of their fossils, it is presumed they were relatively minor components of Mesozoic insect life. The ant fossil record consists of two primary types of fossils, each with inherent biases: as imprints in rock and as inclusions in fossilized resins (amber). New imaging technology allows ancient ant fossils to be examined in ways never before possible. This is particularly helpful because it can be difficult to distinguish true ants from non-ants in Mesozoic fossils. Fossil discoveries continue to inform our understanding of ancient ant morphological diversity, as well as provide insights into their paleobiology.