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Data from: Testing for functional adaptation in a genital bone: Baculum size, shape, and microstructure do not respond plastically to recurrent mating

Dean, Matthew1

Published Sep 10, 2026 on Dryad. https://doi.org/10.5061/dryad.jm63xsjrp

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Sep 10, 2026 version files 139.29 MB

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Abstract

Plasticity – the ability of a genotype to produce different phenotypes in response to environmental input – can be used to infer the mechanical forces experienced by biological structures. Bones are quintessentially plastic, remodeling in response to compression and torsion. The males of many mammal species possess a bone in their penis called a baculum. Across species, its extreme morphological divergence suggests it undergoes recurrent adaptive evolution, and several studies have explicitly linked baculum size and shape to reproductive fitness. However, the precise functions of this bone remain largely unknown. Here we test whether copulation imposes mechanical loading sufficient to induce remodeling in the baculum. We compared bacula of mated vs. unmated males in two different rodent lineages with divergent baculum morphologies and mating ecologies, using high-resolution morphometric and synchrotron-enabled quantification of bone microstructure. We found no consistent differences in size, shape, or microstructure between bacula of mated versus unmated males. These results suggest that the baculum is not subject to mechanical loads strong enough to induce remodelling, and that its rapid evolutionary divergence is not enabled by load-induced plasticity.