TY - JOUR TI - A size principle for recruitment of Drosophila leg motor neurons AU - Azevedo, Anthony W AU - Dickinson, Evyn S AU - Gurung, Pralaksha AU - Venkatasubramanian, Lalanti AU - Mann, Richard S AU - Tuthill, John C A2 - Calabrese, Ronald L A2 - Doe, Chris Q VL - 9 PY - 2020 DA - 2020/06/03 SP - e56754 C1 - eLife 2020;9:e56754 DO - 10.7554/eLife.56754 UR - https://doi.org/10.7554/eLife.56754 AB - To move the body, the brain must precisely coordinate patterns of activity among diverse populations of motor neurons. Here, we use in vivo calcium imaging, electrophysiology, and behavior to understand how genetically-identified motor neurons control flexion of the fruit fly tibia. We find that leg motor neurons exhibit a coordinated gradient of anatomical, physiological, and functional properties. Large, fast motor neurons control high force, ballistic movements while small, slow motor neurons control low force, postural movements. Intermediate neurons fall between these two extremes. This hierarchical organization resembles the size principle, first proposed as a mechanism for establishing recruitment order among vertebrate motor neurons. Recordings in behaving flies confirmed that motor neurons are typically recruited in order from slow to fast. However, we also find that fast, intermediate, and slow motor neurons receive distinct proprioceptive feedback signals, suggesting that the size principle is not the only mechanism that dictates motor neuron recruitment. Overall, this work reveals the functional organization of the fly leg motor system and establishes Drosophila as a tractable system for investigating neural mechanisms of limb motor control. KW - motor control KW - proprioception KW - muscle KW - motor neuron JF - eLife SN - 2050-084X PB - eLife Sciences Publications, Ltd ER -