  With the aim of quantifying the contribution of the environment on the
evolution of galaxies at z=0 we have used the DR7 catalogue of the Sloan
Digital Sky Survey (SDSS) to reconstruct the 3-D distribution of 4132 galaxies
in 420 square degrees of the Coma supercluster, containing two rich clusters
(Coma and A1367), several groups, and many filamentary structures belonging to
the "Great Wall", at the approximate distance of 100 Mpc. At this distance the
galaxy census is complete to Mi=-17.5 mag, i.e. approx 4 mag fainter than M*.
The morphological classification of galaxies into early- (ellipticals) and
late-types (spirals) was carried out by inspection of individual SDSS images
and spectra. The density around each galaxies was determined in cylinders of 1
Mpc radius and 1000 km s^-1 half length. The color-luminosity relation was
derived for galaxies in bins morphological type and in four thresholds of
galaxy density-contrast, ranging from delta{1,1000} <= 0 (UL = the cosmic web);
0 < delta{1,1000} <= 4 (L = the loose groups); 4 < delta{1,1000} <= 20 (H = the
large groups and the cluster's outskirts) and delta{1,1000} > 20 (UH = the
cluster's cores). The fraction of early-type galaxies increases with the log of
the over-density. A well defined "red sequence" composed of early-type galaxies
exists in all environments at high luminosity, but it lacks of low luminosity
(dwarf) galaxies in the lowest density environment. Conversely low luminosity
isolated galaxies are predominantly of late-type. In other words the low
luminosity end of the distribution is dominated by red dE galaxies in clusters
and groups and by dwarf blue amorphous systems in the lowest density regions.
At z=0 we find evidence for strong evolution induced by the environment
(Nurture). Transformations take place mostly at low luminosity when star
forming dwarf galaxies inhabiting low density environments migrate into
amorphous passive dwarf ellipticals in their infall into denser regions. The
mechanism involves suppression of the star formation due to gas stripping,
without significant mass growth, as proposed by Boselli et al. (2008a). This
process is more efficient and fast in ambients of increasing density. In the
highest density environments (around clusters) the truncation of the star
formation happens fast enough (few 100 Myr) to produce the signature of
post-star-burst in galaxy spectra. PSB galaxies, that are in fact found
significantly clustered around the largest dynamical units, represent the
remnants of star forming isolated galaxies that had their star formation
violently suppressed during their infall in clusters in the last 0.5-1.5 Gyrs,
and the progenitors of future dEs.
