Visual trait variation and allometric scaling indicate intra- and inter-caste plasticity in the social wasp Protopolybia sedula.

Understanding how phenotypic plasticity arises in sensory traits is a key challenge in evolutionary and developmental biology. Eusocial insects offer a useful model for exploring it, because their castes perform distinct tasks and occupy different light environments. We examined morphological variation and scaling in the visual systems of female castes of Protopolybia sedula, a neotropical wasp with simultaneous polygyny. Although queens are larger than workers, the two castes showed similar eye area, ommatidial diameter and ommatidia number. However, queens showed greater variability in ommatidial diameter, while workers varied more in eye area and ommatidia number. Allometric patterns also diverged: queen eye area scaled hypoallometrically and ommatidial diameter hyperallometrically with body size, whereas workers displayed isometric scaling for both traits. Analysis of ommatidia size and number indicates workers allocate more resources to increasing ommatidia number, while queens emphasise enlarging ommatidia. These differences highlight distinct developmental and scaling strategies that generate caste-specific visual adaptations.