Tetraploid Caenorhabditis elegans embryos exhibit enhanced tolerance to osmotic stress

Polyploidy is a widespread phenomenon in development and evolution and is often associated with altered cellular physiology and developmental robustness. However, the influence of genome doubling on embryonic robustness to environmental stress remains poorly understood. Here, we investigated developmental traits and osmotic responses in tetraploid Caenorhabditis elegans embryos. Tetraploid animals exhibited enlarged body and tissue sizes and produced embryos with approximately 1.6-fold greater volume than diploids, accompanied by moderately delayed development and partial embryonic arrest. When exposed to a range of osmotic environments, both diploid and tetraploid embryos swelled or shrank in response to external osmolarity. Strikingly, tetraploid embryos at the early stage maintained normal cell division across a broader range of osmotic conditions than diploids. Quantitative analyses further revealed that tetraploid embryos exhibit reduced cytoplasmic mass density, largely reflecting lower protein concentration, while lipid and RNA levels remain unaffected. These compositional differences likely buffer volume fluctuations and underlie the enhanced osmotic tolerance of tetraploid embryos. Our findings demonstrate that genome doubling reshapes embryonic cellular physiology in a non-proportional manner to ploidy, thereby enhancing robustness during early development.