  The mass-metallicity relation (MZR) represents one of the most important
scaling relations in the context of galaxy evolution, comprising a positive
correlation between stellar mass and metallicity (Z). The fundamental
metallicity relation (FMR) introduces a new parameter, the star formation rate
(SFR), in the dependence. While several studies found that Z is anti-correlated
with the SFR at fixed mass, the validity of this statement has been questioned
extensively and no widely-accepted consensus has been reached yet. With this
work, we investigate the FMR in nine nearby, spatially-resolved, dwarf
galaxies, using gas diagnostics on integral-field spectroscopic data of the
Multi Unit Spectroscopic Explorer (MUSE), pushing such investigations to lower
galaxy masses and higher resolutions. We find that both the MZR and FMR exhibit
different behaviours within different star forming regions of the galaxies. We
find that the SFR surface density - metallicity anti-correlation is tighter in
the low-mass galaxies of our sample. For all the galaxies considered, we find a
SFR surface density - stellar mass surface density correlation. We propose that
the main reason behind these findings is connected to the accretion mechanisms
of the gas fuelling star formation -- low-mass, metal-poor galaxies accrete
pristine gas from the intergalactic medium, while in more massive and
metal-enriched systems the gas responsible for star formation is recycled from
previous star forming episodes.
