Tetraploid Caenorhabditis elegans embryos exhibit enhanced tolerance to osmotic stress

Polyploidy is a widespread phenomenon in development and evolution and is frequently associated with altered cellular physiology and developmental robustness. However, how genome doubling influences an embryonic robustness to environmental stress remains poorly understood. Here, we investigated developmental traits and osmotic responses in tetraploid Caenorhabditis elegans embryos. Tetraploid animals exhibited increased body and tissue sizes and produced larger embryos 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 exhibited reduced cytoplasmic mass density, primarily reflecting lower protein concentration, while lipid and RNA levels remain unaffected. These compositional differences likely buffer cellular size fluctuations and underlie the enhanced osmotic tolerance of tetraploid embryos. Together, our findings demonstrate that genome doubling reshapes embryonic cellular physiology in a non-proportional manner to ploidy, thereby enhancing robustness during early development.