Benjamin de Bivort
Thomas D. Cabot Associate Professor of Organismic and Evolutionary Biology
Harvard University, Department of OEB
The Neurobiology of Individuality
Abstract: Indviduals exhibit strikingly different patterns of behavior even when they share the same genome and macroscopic environment. This challenges the aphorism that biological variation comes from “nature” or “nurture.” Variation must come from other sources, namely stochastic variation in developmental outcomes (like the wiring of synapses, transcriptional fluctuations or noise in neural signaling). Such processes likely underlie personality (as well as our sense of individuality) and variability in psychiatric disease penetrance. Using the fruit fly Drosophila melanogaster, we have characterized behavioral individuality in a diverse suite of stimulus-evoked and spontaneous behaviors with multidimensional variation across individuals. Taking advantage of the fly’s relatively small, extensively mapped nervous system and deep genetic toolkit, we have discovered genetic and neural circuit mechanisms regulating the extent of behavioral variability. We have also begun to identify specific sites in the brain where individual neuroanatomical differences drive behavioral differences (“loci of individuality”). Specifically, we have mapped sites in olfactory and pre-motor circuits where the idiosyncratic extent of pre-synaptic active zones in specific neural compartments (olfactory receptor neuron axon terminals in glomeruli of the antennal lobe and central complex output neuron axons in the lateral accessory lobe) predicts individual odor preferences and locomotor biases, respectively. As a lab, we aspire to an integrative understanding of behavioral individuality, and alongside mechanistic circuit studies, we have investigated the ecological and evolutionary significance of behavioral individuality. Recently collected behavioral data from wild flies, sampled across the US, are consistent with theoretical predictions that variability in individual thermal preference reflects an evolutionary strategy of bet-hedging against seasonal temperature fluctuations. Thus, flies may exploit neural circuit stochasticity to implement a phenotypic diversification strategy that helps them survive in a fluctuating environments.