Neither nature nor nurture: Behavioral individuality in fruit flies’ neurodevelopmental origin

While some fruit flies wander, others prefer to walk the straight and narrow; the origin of these behavioral quirks in individual flies may be a product of random variation in how neural circuits are wired during brain development, a new study of fruit flies given “lines to walk” finds. Its authors say the inherent chaos of normal neurodevelopment is key to generating behavioral diversity in a genetically similar population, and that similar mechanisms may exist in other species, including humans. Much of our understandings about the origins of behavioral individuality in animals is dominated by the paradigm of “nature” (the inherited genome as a driver of consequences) versus “nurture” (experience and environment as a driver). However, in almost all animals, unique behavioral idiosyncrasies are as common as natural developmental variation in brain anatomy, even between genetically identical individuals. Whether individual differences in brain development predict individuals’ behaviors remains unexplored. Linneweber and colleagues describe a non-heritable neurodevelopmental origin for behavioral individuality in

Drosophila

fruit flies. When given lines to follow, some freely walking flies tend to walk narrower paths, while others wander. Here, Linneweber et al. show how individual variation in how a set of visual system neurons called the dorsal cluster neurons (DCN) are wired leads to the emergence of individuality in a fly’s line-walking behavior. Random variation in DCN development results in brain circuit asymmetry unique to each fly, which significantly guided their behavior. The results reveal that flies with more asymmetric DCN wiring were better able to orient to the line, and thus exhibited straighter line-walking behaviors. The work establishes a link between random neural variation and individuality of animal behavior.

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