DOI: 10.5061/dryad.fxpnvx110
title: Linking shape conspicuous asymmetry with shape covariation patterns and performance in the insect head and mandibles

description: 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 morphology by
 having interlocking shapes, the developmental modularity required to
 achieve this seems to be overwritten by developmental and/or functional
 integration, allowing the precise matching required for feeding. The
 consequent conflicting covariation patterns are reminiscent of the
 palimpsest model. Finally, the degree of directional asymmetry appears to
 be under selection, although we find no relationship between bite force
 and mandible shape or asymmetry.
description: The dataset consists of raw image stacks of CT scans of several
 <em>Schistocerca gregaria</em> (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.
description: # 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 file names are composed of the name of their corresponding TIF or RAW file, with \_REPLICATE added for the second round of digitization. ## Sharing/Access information NA ## Code/Software NA