Microevolutionary Divergence and Plasticity of Laryngeal Shape in the House Mouse (Mus musculus).

The morphology of the larynx is essential for vocalization, respiration, and airway protection, yet the sources of phenotypic variation within species are not well understood. This study investigated whether genetic background exerts a stronger influence than environmental factors on laryngeal morphology in two house mouse strains. Using geometric morphometrics, we analyzed the size and shape of 87 laryngeal specimens and examined the effects of body size, genetics, obesity, exercise, and social housing. Our results demonstrate that genetic background significantly shapes laryngeal structure. There were significant shape differences between the two genetic strains, and the inbred strain showed less phenotypic variation than the outbred mice. Although these structural differences likely arose without direct selection, they were associated with marginal differences in vocal output, suggesting functional relevance. Obesity and exercise also influenced laryngeal morphology, but their effects were secondary to genetics. Notably, leptin levels were linked to size and shape changes in the vocal organ. These findings suggest that random genetic drift and pleiotropy can be important drivers of laryngeal evolution in house mice. Overall, both genetic and environmental factors contribute to laryngeal shape, underscoring the organ's plasticity.