Latent effect of larval rearing environment on post-metamorphic brain growth in an anuran amphibian

Early development is highly susceptible to environmental influence. We evaluated the role of larval visual environment on brain morphology plasticity in late larval and juvenile stages of Bombina orientalis, an anuran amphibian changing from an aquatic to a terrestrial habitat after metamorphosis. Manipulation of the visual environment was achieved by rearing larvae in normal and darkened water. The juveniles were exposed to normal lighting conditions after metamorphosis, allowing to assess if plastic effects persisted or emerged after metamorphosis. The darkness treatment accelerated development before slowing it down substantially, allowing controls to metamorphose earlier. Although larvae reared in darkened water had the same relative brain size as controls by the end of the larval period, juveniles that had been reared in darkened water as larvae had brains that were 14.4% smaller than juveniles that had been reared under control conditions. Conversely, relative telencephalon size was 6.7% larger in juveniles previously reared in darkened water compared with controls, again with no effect of darkened water seen by the end of the larval period. Unlike the latent effects seen on whole brain and telencephalon size, relative size of the optic tectum was significantly smaller in both larvae and juveniles exposed to the darkened water treatment. Therefore, the effects of visual restriction on juvenile brain form were a combination of latent (whole brain and telencephalon) and carry-over (optic tectum) developmental effects.