Аннотация:The nonlinear evolution of the electron distribution function in collisionless magnetic field line reconnection is investigated by adopting a drift-kinetic description of the electron response. A two dimensional magnetic configuration with a null line and a strong perpendicular guide magnetic field is considered. Using the conservation of the parallel canonical momentum, the fluid and the drift-kinetic regimes of the collisionless reconnection instability are shown to share common features in terms of the advection and mixing of the Lagrangian invariants.