The role of the sex determination cascade in the development of caste polyphenisms.

The evolution of complex insect societies, characterized by a reproductive division of labor between queens and workers, represents a major evolutionary transition. Yet, the molecular mechanisms governing caste differentiation remain only partially understood. We summarize recent research advancements in ants and bees with a focus on corbiculate bees, a group of immense ecological and economic importance displaying a broad spectrum of sociality. Caste determination is a result of developmental plasticity, typically initiated by nutritional cues during the larval stage that activate conserved pathways involving Insulin and juvenile hormone signaling. However, recent evidence highlights a deeper integration with fundamental developmental pathways, such as the sex-determination pathway and patterning genes, which regulate sex- and caste-specific trait polyphenisms, such as eye morphology, reproductive organ size, the corbiculum, and social behaviors. Mechanisms like alternative splicing and spatio-temporal gene expression are emerging as key regulators of these plastic phenotypes. Significant knowledge gaps remain due to biases toward honeybees and females. We advocate for future research to adopt a broader comparative evo-devo framework, including underrepresented groups like stingless bees, social parasites, and males. Employing integrative approaches, such as long-read and spatial transcriptomics across multiple tissues and developmental stages, will be crucial for a comprehensive understanding of how developmental plasticity shapes and drives the evolution of caste-specific traits related to social complexity.