Gerit Arne Linneweber

Highlights • Developmental temperature affects synapse numbers and partner availability in flies • Development at 18°C results in synaptic partnerships absent at 25°C • The same non-canonical synapses form at 18°C and in the absence of a main partner at 25°C • Adult behavioral activity is adapted for the temperature at which the fly developed Summary Variability of synapse numbers and partners despite identical genes reveals the limits of genetic determinism.

Abstract Brain wiring is remarkably precise, yet most neurons readily form synapses with incorrect partners when given the opportunity. Dynamic axon-dendritic positioning can restrict synaptogenic encounters, but the spatiotemporal interaction kinetics and their regulation remain essentially unknown inside developing brains. Here we show that the kinetics of axonal filopodia restrict synapse formation and partner choice for neurons that are not otherwise prevented from making incorrect synapses.

Diversity from development When given a line to follow, some fruit flies do so carefully and others weave. Linneweber et al. now show that these behaviors are stable for an individual but diverse in an isogenic population. Key to generating individual diversity in the population is the inherent chaos of normal development. A set of neurons in the visual system is wired up in a variable manner, resulting in brain circuit asymmetry unique to each fly that guides its line-walking behavior.