Supplementary Material for: Allometric Brain Development and Neuroecological Adaptations in Juvenile and Adult Raja polistigma

Chondrichthyans represent some of the earliest diverging lineages of jawed vertebrates, making them valuable models for studying vertebrate evolution. Many studies have explored how variations in brain anatomy relate to behaviour and ecological roles. This study examines the postnatal brain development and neuroecological adaptations in the speckled skate, Raja polystigma, which is an endemic species of the Mediterranean Sea, an understudied biodiversity hotspot for Chondrichthyan’ brain evolution. Its distinct life-history traits, including bathymetric segregation and shifts in feeding habits, made it a valuable model for studying how ecological factors shape brain development in benthic cartilaginous fishes. We focused on the allometry between brain mass and body mass, as well as the relative size of specific brain regions and the brain mass. Our analysis shows that as body mass increases, brain growth slows down relative to body growth, which may be linked to the skate reaching adulthood and sexual maturity. We also found that certain brain regions, like the olfactory bulbs, medulla oblongata, and cerebellum grow faster than the rest of the brain, suggesting these areas enhance sensory and motor functions as the skate grows. In contrast, the optic tectum tends to grow slower, possibly indicating a reduced reliance on vision in adults. The telencephalon and diencephalon grow at the same rate as the rest of the brain, which may support consistent cognitive and sensory functions throughout postnatal development. These findings help us to understand how the species adapts to its environment, with important implications for sensory specialization during its growth.