# Phylogenetic and Morphological Analysis of Wing Base Articulation in Vespidae (Hymenoptera): A Cladistic Approach

## TL;DR

This study explores wing base structures in wasps, revealing new insights into their function and evolution, and challenges previous assumptions about their classification.

## Contribution

The paper introduces detailed articulation models and corrects prior misconceptions about axillary sclerites in Vespidae wasps.

## Key findings

- The first axillary sclerite has a sclerotized knob influencing wing articulation.
- The second axillary sclerite is a single triangular structure with three attachment points.
- Phylogenetic analysis based on wing-base morphology does not support Vespidae as monophyletic.

## Abstract

The study identifies previously overlooked variation in wing base sclerites among vespid wasps and explains how these structures support folding, control, and stability of the wings. Distinct features of the first, second, and third axillary sclerites, along with the basiradial bridge, show clear functional and evolutionary patterns within the family. Forewing and hindwing base characters were coded for sixteen vespid taxa and Xyela sp., but the resulting topology does not recover Vespidae as monophyletic under the present morphological dataset. The work also corrects earlier ideas regarding the presence of a fourth axillary sclerite. It introduces detailed articulation models and muscle sketches that provide a firmer basis for future biomechanical and comparative studies.

Insect wing base sclerites are crucial to wing function and evolution, yet their diversity beyond order-level comparisons remains poorly understood. We examine variation in wing base sclerites across Vespidae, focusing on the axillary sclerites (1Ax, 2Ax, and 3Ax), the shoulder sclerite, and associated structures. The first axillary sclerite shows distinct regional differentiation and bears a well-sclerotized knob that influences wing articulation. Additionally, 2Ax in Vespidae is a single, triangular structure with three attachment points, distinct from the two-part composition in some other wasps, which facilitates high-frequency wing vibrations. Our findings also highlight variable fusion patterns in 3Ax and its interaction with 2Ax, contributing to wing flexibility. The basiradial bridge, connecting the subcostal and radial veins, reinforces wing stability and articulation. Phylogenetic analysis based on wing-base morphology does not support the monophyly of Vespidae and differs from molecular hypotheses, but it refines previous morphological interpretations. The well-supported subfamily relationships confirm Vespinae as a monophyletic group and reveal a close association among Polistinae, Stenogastrinae, and Eumeninae, as represented by Polistes, Eustenogaster, and Oreumenes, respectively, suggesting evolutionary transitions in social behavior within the family Vespidae. The absence of a fourth axillary sclerite challenges earlier hypotheses, providing new insights into Hymenopteran wing base evolution. Two articulation models are proposed for forewings and hindwings, supported by three-dimensional reconstructions of axillary sclerites, indirect and direct flight muscles, and their attachment sites. These results refine interpretations of wasp wing mechanics, evolution, and morphological diversification across taxa.