  We investigate the mass loss of galaxies in groups and clusters with
high-resolution DM simulations. We detect weak mass segregation in the inner
regions of group/cluster haloes, consistent with observational findings. This
applies to samples of galaxy analogues selected using either their present-day
mass or past maximum (peak) mass. We find a strong radial trend in the
fractional mass lost by the galaxies since peak, independent of their mass.
This suggests that segregation is due to massive galaxies having formed closer
to the halo centres and not the preferential destruction of smaller galaxies
near halo centres. We divide our sample into galaxies that were accreted as a
group vs. as a single, distinct halo. We find strong evidence for preprocessing
-- the grouped galaxies lose $\sim 35-45\%$ of their peak mass before being
accreted onto their final host haloes, compared to single galaxies which lose
$\sim12\%$. After accretion, however, the single galaxies lose more mass
compared to the grouped ones. These results are consistent with a scenario in
which grouped galaxies are preprocessed in smaller haloes while single galaxies
`catch up' in terms of total mass loss once they are accreted onto the final
host halo. The fractional mass loss is mostly independent of the galaxy mass
and host mass, and increases with amount of time spent in a dense environment.
