Morphology of the metapleural gland and its associated novel atrial cone gland in Strumigenys ants.

The metapleural gland is a unique feature of the ant phenotype, but diversity in its anatomy and function across the ants is not well documented or understood. We studied the morphology of the metapleural gland in 20 mainly Oriental Strumigenys species using histology, scanning and transmission electron microscopy, and micro-CT. The gland is formed by a cluster of class-3 cells, their secretion is transported through a bundle of ducts into the sclerotized atrium and is guided along a series of parallel cuticular ridges towards the atrial opening. Among the examined species, queens have more gland cells than conspecific workers, while the examined males do not have the gland. The social parasite S. mutica has the most developed metapleural gland. In addition, we describe a novel class-1 atrial cone gland which is associated with the metapleural gland. The epithelium of this cone gland forms an invagination into the ventral atrium of the metapleural gland. The cuticular cone may be lacking in some Afrotropical and Neotropical species, although these may still contain the epithelial gland. The functional and evolutionary drivers of morphological variation in the exocrine system across species form interesting questions for future work.

A Roadmap to Reconstructing Muscle Architecture from CT Data.

Skeletal muscle is responsible for voluntary force generation across animals, and muscle architecture largely determines the parameters of mechanical output. The ability to analyze muscle performance through muscle architecture is thus a key step towards better understanding the ecology and evolution of movements and morphologies. In pennate skeletal muscle, volume, fiber lengths, and attachment angles to force transmitting structures comprise the most relevant parameters of muscle architecture. Measuring these features through tomographic techniques offers an alternative to tedious and destructive dissections, particularly as the availability of tomographic data is rapidly increasing. However, there is a need for streamlined computational methods to access this information efficiently. Here, we establish and compare workflows using partially automated image analysis for fast and accurate estimation of animal muscle architecture. After isolating a target muscle through segmentation, we evaluate freely available and proprietary fiber tracing algorithms to reconstruct muscle fibers. We then present a script using the Blender Python API to estimate attachment angles, fiber lengths, muscle volume, and physiological cross-sectional area. We apply these methods to insect and vertebrate muscle and provide guided workflows. Results from fiber tracing are consistent compared to manual measurements but much less time-consuming. Lastly, we emphasize the capabilities of the open-source three-dimensional software Blender as both a tool for visualization and a scriptable analytic tool to process digitized anatomical data. Across organisms, it is feasible to extract, analyze, and visualize muscle architecture from tomography data by exploiting the spatial features of scans and the geometric properties of muscle fibers. As digital libraries of anatomies continue to grow, the workflows and approach presented here can be part of the open-source future of digital comparative analysis.

O músculo esquelético é responsável pela geração de força voluntária em animais, e a arquitetura muscular determina em grande parte os parâmetros de performance mecânica. A capacidade de analisar o desempenho muscular através da arquitetura muscular é, portanto, um passo fundamental para uma melhor compreensão da ecologia e evolução dos movimentos e morfologias. No músculo esquelético penado, o volume, o comprimento das fibras e os ângulos de fixação às estruturas de transmissão de força constituem os parâmetros mais relevantes da arquitetura muscular. A medição dessas propriedades por meio de técnicas tomográficas oferece uma alternativa às dissecções tediosas e destrutivas, especialmente pelo rápido aumento na disponibilidade de dados tomográficos. No entanto, há uma necessidade de métodos computacionais otimizados para acessar essas informações de forma eficiente. Aqui, estabelecemos e comparamos fluxos de trabalho usando análise parcialmente automatizada de imagem para estimativa rápida e precisa da arquitetura muscular em animais. Após isolar um músculo alvo por meio de segmentação, avaliamos os algoritmos disponíveis gratuitamente e pagos para o rastreamento de fibra (Fiber Tracing) para reconstruir as fibras musculares. Apresentamos um script que usa a API do Blender Python para estimar os ângulos de ligamento, o comprimento da fibra, o volume do músculo e a secção transversal fisiológica. Aplicamos esses métodos aos músculos de insetos e vertebrados e fornecemos instruções detalhadas de uso. Os resultados do rastreamento de fibra são consistentes em comparação com as medições manuais, mas requerem menos tempo. Finalmente, enfatizamos a capacidade do software de modelagem de código aberto Blender 3D tanto como uma ferramenta de visualização programável quanto uma ferramenta analítica para processar dados anatômicos digitalizados. Para muitos organismos, é possível extrair, analisar e visualizar a arquitetura muscular, explorando as características espaciais das tomografias e as propriedades geométricas das fibras musculares. À medida que as bibliotecas de anatomia digital continuam a crescer, os fluxos de trabalho e a abordagem apresentados aqui podem fazer parte do futuro da análise comparativa digital de código aberto.

El músculo esquelético es responsable de la generación de fuerza voluntaria en los animales y la arquitectura muscular determina en gran medida los parámetros de producción mecánica. La capacidad de analizar el rendimiento muscular a través de la arquitectura muscular es, por tanto, un paso clave hacia una mejor comprensión de la ecología y evolución de los movimientos y morfologías. En el músculo esquelético pennado, el volumen, la longitud de las fibras y los ángulos de fijación a las estructuras de transmisión de fuerza comprenden los parámetros más relevantes de la arquitectura muscular. La medición de estas características mediante técnicas tomográficas ofrece una alternativa a las disecciones tediosas y destructivas, sobre todo porque la disponibilidad de datos tomográficos está aumentando rápidamente. Sin embargo, existe la necesidad de métodos computacionales optimizados para acceder a esta información de manera eficiente. Aquí, establecemos y comparamos flujos de trabajo utilizando análisis de imágenes parcialmente automatizados para una estimación rápida y precisa de la arquitectura del músculo animal. Después de aislar un músculo objetivo a través de la segmentación, evaluamos algoritmos de trazado de fibras ("Fiber Tracing") patentados y gratuitos para reconstruir las fibras musculares. Presentamos un script que utiliza la API de Blender Python para estimar los ángulos de penación, la longitud de las fibras, el volumen muscular y el área de sección transversal fisiológica. Aplicamos estos métodos a los músculos de insectos y vertebrados y proporcionamos flujos de trabajo guiados. Los resultados del rastreo de fibras son consistentes en comparación con las mediciones manuales, pero requieren mucho menos tiempo. Por último, enfatizamos las capacidades del software 3D de código abierto Blender como herramienta de visualización y herramienta analítica programable para procesar datos anatómicos digitalizados. Por muchos organismos, es factible de extraer, analizar y visualizar la arquitectura muscular mediante la explotación de las características espaciales de las tomografías y las propiedades geométricas de las fibras musculares. A medida que las bibliotecas digitales de anatomías continúan creciendo, los flujos de trabajo y el enfoque presentados aquí pueden ser parte del futuro de código abierto del análisis comparativo digital.

Pheidoleklaman sp. nov.: a new addition from Ivory Coast to the Afrotropical pulchella species group (Hymenoptera, Formicidae, Myrmicinae).

In this study the taxonomy of the Pheidolepulchella species group is updated for the Afrotropical region and the new species P.klaman sp. nov. described. It is integrated into the existing taxonomic system by an updated identification key for the whole group and an update of the known distribution ranges of its members. High quality focus stacking images are provided, with X-ray micro-CT scanned digital 3D representations, of major and minor worker type specimens.

The loss of flight in ant workers enabled an evolutionary redesign of the thorax for ground labour.

BACKGROUND: Explanations for the ecological dominance of ants generally focus on the benefits of division of labour and cooperation during foraging. However, the principal innovation of ants relative to their wasp ancestors was the evolution of a new phenotype: a wingless worker caste optimized for ground labour. Ant workers are famous for their ability to lift and carry heavy loads, but we know surprisingly little about the morphological basis of their strength. Here we examine the consequences of the universal loss of flight in ant workers on skeletomuscular adaptations in the thorax for enhanced foraging on six legs. RESULTS: Using X-ray microcomputed tomography and 3D segmentation, we compared winged queens and wingless workers in Euponera sikorae (subfamily Ponerinae) and Cataglyphis savignyi (subfamily Formicinae). Workers are characterized by five major changes to their thorax: i) fusion of the articulated flight thorax (queens) into a rigid box optimized to support the muscles that operate the head, legs and abdomen, ii) redesign of internal cuticular structures for better bracing and muscle attachment, iii) substantial enlargement of the neck muscles for suspending and moving the head, iv) lengthening of the external trochanter muscles, predominant for the leg actions that lift the body off the ground, v) modified angle of the petiole muscles that are key for flexion of the abdomen. We measured volumes and pennation angles for a few key muscles to assess their increased efficacy. Our comparisons of additional workers across five genera in subfamilies Dorylinae and Myrmicinae show these modifications in the wingless thorax to be consistent. In contrast, a mutillid wasp showed a different pattern of muscle adaptations resulting from the lack of wing muscles. CONCLUSIONS: Rather than simply a subtraction of costly flight muscles, we propose the ant worker thorax evolved into a power core underlying stronger mandibles, legs, and sting. This contrasts with solitary flightless insects where the lack of central place foraging generated distinct selective pressures for rearranging the thorax. Stronger emphasis is needed on morphological innovations of social insects to further our understanding of the evolution of social behaviours.

Giant ants and their shape: revealing relationships in the genus Titanomyrma with geometric morphometrics.

Shape is a natural phenomenon inherent to many different lifeforms. A modern technique to analyse shape is geometric morphometrics (GM), which offers a whole range of methods concerning the pure shape of an object. The results from these methods have provided new insights into biological problems and have become especially useful in the fields of entomology and palaeontology. Despite the conspicuous successes in other hymenopteran groups, GM analysis of wings and fossil wings of Formicidae has been neglected. Here we tested if landmarks defining the wing shape of fossil ants that belong to the genus Titanomyrma are reliable and if this technique is able to expose relationships among different groups of the largest Hymenoptera that ever lived. This study comprises 402 wings from 362 ants that were analysed and assigned with the GM methods linear discriminant function analysis, principal component analysis, canonical variate analysis, and regression. The giant ant genus Titanomyrma and the parataxon Formicium have different representatives that are all very similar but these modern methods were able to distinguish giant ant types even to the level of the sex. Thirty-five giant ant specimens from the Eckfeld Maar were significantly differentiable from a collection of Messel specimens that consisted of 187 Titanomyrma gigantea females and 42 T. gigantea males, and from 74 Titanomyrma simillima females and 21 T. simillima males. Out of the 324 Messel ants, 127 are newly assigned to a species and 223 giant ants are newly assigned to sex with GM analysis. All specimens from Messel fit to the two species. Moreover, shape affinities of these groups and the species Formicium brodiei, Formicium mirabile, and Formicium berryi, which are known only from wings, were investigated. T. gigantea stands out with a possible female relative in one of the Eckfeld specimens whereas the other groups show similar shape patterns that are possibly plesiomorphic. Formicidae are one of the most dominant taxa in the animal kingdom and new methods can aid in investigating their diversity in the present and in deep time. GM of the ant wing delivers significant results and this core of methods is able to enhance the toolset we have now to analyse the complex biology of the ants. It can prove as especially useful in the future when incorporated into better understanding aspects of evolutionary patterns and ant palaeontology.