Comparative study of the sensory system between surface and cave dwelling populations of the amphipod Gammarus minus

In this study, a comparison of the brain region sizes and morphology was done between individuals of spring and cave dwelling populations of the amphipod Gammarus minus. The particular areas of interest, in the brain of these animals, were the protocerebrum at the optic lamina ganglionaris (optic ganglion) level and the deuterocerebrum at the olfactory lobe level. The animals' heads were fixed with Karnovsky's fixative, dehydrated, embedded in Immuno-bed, sectioned and stained with toluidine blue and eosin. Semi-serial sections were examined and the results showed that the external differences between both populations were also seen at the brain level. In other words, the diameter of the optic ganglion is significantly larger in the spring populations while the diameter of the olfactory lobe is significantly larger in the cave populations, suggesting a pattern of adaptation to the habitats.