  Multiple populations (MPs), characterized by variations in light elemental
abundances, have been found in stellar clusters in the Milky Way, Magellanic
Clouds, as well as several other dwarf galaxies. Based on a large amount of
observations, mass has been suggested to be a key parameter affecting the
presence and appearance of MPs in stellar clusters. To further investigate the
existence of MPs in low-mass clusters and explore the mass threshold for MP
formation, we carried out a project studying the stellar population composition
in several low-mass Galactic globular clusters. Here we present our study on
the cluster Eridanus. With blue-UV low-resolution spectra obtained with the
OSIRIS/Multi-object spectrograph on the Gran Telescopio Canarias, we computed
the spectral indices of CH and CN for the sample giant stars, and derived their
carbon and nitrogen abundances using model spectra. A significant dispersion in
the initial surface abundance of nitrogen was found in the sample, indicating
the existence of MPs in Eridanus. Inspecting the age-initial mass distribution
of in-situ clusters with MPs, we find a slight trend that initial mass
increases with increasing age, and the lowest initial mass of log Minitial
~4.98 and 5.26 are found at the young and old end, respectively, which might
provide a rough reference for the mass threshold for clusters to form MPs.
However, more observations of clusters with low initial masses are still
necessary before any firm conclusion can be drawn.
