which they interpreted as being the effect of lower gas-phase metallicities.

As previously mentioned, the results of @Umeda:1998ij indicate that the maximum CO WD mass remains close to $\sim 1.1\,M_\odot$ over a wide range of metallicities. If this is true, and binary evolution effects are neglected, then we would expect the relative rates of super-Chandrasekhar SNe Ia arising from mergers to increase with lower metallicity in proportion to the normal SNe Ia due to the power law form of the IMF (note that instabilities prohibit the necessary growth of even rapidly-rotating single WDs; @Piro:2008pr). However, recent observations of host galaxies may indicate an even stronger preference for low-metallicity hosts for super-Chandrasekhar SNe Ia (e.g., @Taubenberger:2010qv [@Childress:2011hg]). Moreover, the maximum mass resulting from a merger under these assumptions is $\sim 2.2\,M_\odot$, well below that inferred from SN 2007if [@Scalzo:2010xd].

An explanation for both effects may arise from binary evolution. To achieve a higher total merger mass, without resorting to an ONeMg WD, at least one WD should gain mass while maintaining a CO composition. If the effect of inhibiting single degenerate SN Ia production at $Z \lesssim 0.1\,Z_\odot$ [@Kobayashi:1998ii; @Kobayashi:2008se] does hold, then the primary WD may instead be pushed close 