A COMPARISON BETWEEN AN ANCESTRAL AND A DERIVED CRUSTACEAN BRAIN

Abstract

The goal of my research is to investigate which neurons in the brains of a crustacean species might be involved in pathways or circuits underlying sensory convergence and learning and memory. The first step in such an investigation is an analysis of neuron organization, using histological comparisons across identified centers that are known from other studies to serve multisensory integration and possibly learning and memory. The main goal of this research has been to analyze the morphology of a highly derived malacostracan crustacean (crab) brain, comparing it with the brain of a well-documented basal malacostracan belonging to Stomatopoda. The stomatopod learning and memory center consists of a cap and stalk, as in an insect’s mushroom body–a center known to support learning and memory. In contrast, the crab’s center comprises a saddle-like structure, which in the literature is known as a hemiellipsoid body, situated over the rostral surface of the lateral protocerebrum. In stomatopods, input and output neurons extend their branches into the mushroom body where they intersect parallel fibers. In the crab, there are no such obvious arrangements of fibers. My goal is to determine if there is evidence that, during the course of evolution, there has been a discrete modification of the organization in homologous computational circuits in the crab lineage (Brachycera). In order to complete this task, I have generated histological silver-stained preparations that allowed direct comparison of stomatopod and crab centers. I also had access to a library of Golgi stained specimens of both species investigated. These specimens provide crucial information about the shapes of single neurons.