Development and evolution of higher brain centers in insects

Brain structures within an individual can change during development through modification of individual neuron morphology together with alteration of neuron numbers. Differences in the same or analogous brain structures from different species can reflect behavioral pattern variation among these species fixed by natural selection. This study used insects from two different taxonomic groups to address such brain structure changes at these two time scales: developmental and evolutionary. Mushroom bodies, as an integrative sensory center involved in learning and memory in insects, were the main structure surveyed to illustrate changes in higher brain centers in both projects. In the developmental study, the changes of higher brain centers in red flour beetle, Tribolium castaneaum, were described from late larva through adulthood. The mechanisms detected for change of brain included axon reorganization, compartment enlargement and adult neurogenesis. In a second study to comparing brain structure differences across species, with an effort to address an evolutionary question, a significant difference in mushroom body volumes from different species of eusocial termites was found. This suggests that it is possible to independently test the social brain hypothesis, which was developed for very different animal lineages including primates, within this group of successful social insects.