Abstract

Despite being a fundamental question in Biology, the evolution of animal behaviour remains poorly understood. The divergence of behaviours has been correlated with neuronal circuit changes between species or with distinct genetic makeups, but actual demonstrations of the genetic processes that have taken place to drive the emergence of new behaviours have only been achieved in the sensory system in the context of receptor expression (Auer et al., Nature 2020). Here, we show that by merely tweaking the levels of expression of the key developmental Hox genes, different circuits with different behavioural outputs can be generated. This change occurs only at the final steps of embryonic development, refining connectivity in an otherwise unchanged system. In other words, rather than requiring specific developmental blueprints for each motor circuit—in the case of the fruit fly, those governing, rolling, turning, crawling, etc.—a single blueprint is used, with gene expression levels at the final stages determining the final designation of each circuit. Such a mechanism ensures the system stability and simplifies circuit diversification—within organisms and potentially also across all organisms.