  At nonzero lattice spacing the QCD partition function with Wilson quarks
undergoes either a second order phase transition to the Aoki phase for
decreasing quark mass or shows a first order jump when the quark mass changes
sign. We discuss these phase transitions in terms of Wilson Dirac spectra and
show that the first order scenario can only occur in the presence of dynamical
quarks while in the quenched case we can only have a transition to the Aoki
phase. The exact microscopic spectral density of the non-Hermitian Wilson Dirac
operator with dynamical quarks is discussed as well. We conclude with some
remarks on discretization effects for the overlap Dirac operator.
