Linking shape conspicuous asymmetry with shape covariation patterns and performance in the insect head and mandibles

Bilateral symmetry is widespread across animals, yet, among bilaterians, many cases of conspicuous asymmetries evolved. This means that bilaterally homologous structures on the left and right sides display divergent phenotypes. The evolution of such divergent phenotypes between otherwise similarly shaped structures can be thought to be favoured by modularity, but this has rarely been studied in the context of left-right differences. Here, we provide an empirical example, using geometric morphometrics, to assess patterns of asymmetry and covariation between landmark partitions in a grasshopper with conspicuously asymmetric mandibles. Our morphometric data confirms the presence of strictly directional conspicuous asymmetry in the mandibles and surrounding structures. Covariance patterns and tests hint at a strong integration between mandibles despite their divergent morphologies, and variational modularity with the head capsule. While mandibles have been selected to achieve a key-and-lock..., The dataset consists of raw image stacks of CT scans of several Schistocerca gregaria (grasshoppers) heads, and the landmarks digitized on these heads. The animals were purchased from a commercial pet shop (Fressnapf) in Bonn. CT scans were acquired on Bouin solution fixed heads with mandibles fully closed, using a Bruker SkyScan 1272 (Voltage = 50 kV, current = 200 µA, image pixel size = 6.0 µm or 7.5 µm) and reconstructed using NRecon (Bruker). Landmarks were digitized in the software Morphodig v. 1.6.7 (Lebrun, 2018), and replicated once for all specimens., , # Linking shape conspicuous asymmetry with shape covariation patterns and performance in the insect head and mandibles

[https://doi.org/10.5061/dryad.fxpnvx110](https://doi.org/10.5061/dryad.fxpnvx110)

The dataset consists of raw image stacks of CT scans of several *Schistocerca gregaria* (grasshoppers) heads, and the landmarks digitized on these heads.

## Description of the data and file structure

The CT scan files are provided as TIF image stacks or in RAW format. Filenames or the Raw files contain information about the file including the identifier of the individual, the dimensions of the scan, the bit depth, and the voxel size, formatted as follows: identifier_small_dimensionxdimensionxdimension_bitdepth_voxelsize.raw. The TIF files only contain information on the individual identifier (different sequence from the RAW files).

The landmark files are provided as TPS (text) files, with two files corresponding to each head scan, because the digitization was replicated once. TPS fil...