  We study the evolution of spectral early-type galaxies in clusters, groups
and the field up to redshift 0.9 using the EDisCS dataset. We measure Re, Ie,
and sigma for 154 cluster and 68 field galaxies. We study the evolution of the
zero point of the fundamental plane (FP) and confirm results in the literature,
but now also for the low cluster velocity dispersion regime. The mass-to-light
ratio varies as Delta log M/L_B=(-0.54+-0.01)z=(-1.61+-0.01)log(1+z) in
clusters, independent of their velocity dispersion. The evolution is stronger
(Delta log M/L_B=(-0.76+-0.01)z=(-2.27+-0.03)log(1+z)) for field galaxies. The
FP residuals correlate with galaxy mass and become progressively negative at
low masses. The effect is visible at z>=0.7 for cluster galaxies and at z>=0.5
for field galaxies. We investigate the size evolution of our galaxy sample. We
find that the half-luminosity radius for a galaxy with a dynamical or stellar
mass of 2x10^11 Msol varies as (1+z)^{-1.0+-0.3} for both cluster and field
galaxies. At the same time, stellar velocity dispersions grow with redshift, as
(1+z)^{0.59+-0.10} at constant dynamical mass, and as (1+z)^{0.34+- 0.14} at
constant stellar mass. The measured size evolution reduces to Re (1+z)^{-0.5+-
0.2} and sigma (1+z)^{0.41+-0.08}, at fixed dynamical masses, and Re
(1+z)^{-0.68+-0.4} and sigma (1+z)^{0.19+-0.10}, at fixed stellar masses, when
the progenitor bias (galaxies that locally are of spectroscopic early-type, but
not very old, disappear from the EDisCS high-redshift sample; these galaxies
tend to be large in size) is taken into account. Taken together, the variations
in size and velocity dispersion imply that the luminosity evolution with
redshift derived from the zero point of the FP is somewhat milder than that
derived without taking these variations into account.
