Bi-directional efects of vitamin B12 and methotrexate on Daphnia magna ftness and genomic methylation

Here we interrogated, using three separate but complementary experimental approaches, the impact of vitamin B12 availability and methotrexate exposure on Daphnia magna, which we hypothesised should have an opposite efect on One carbon metabolism (OCM). OCM is a vital biological process supporting a variety of physiological processes, including DNA methylation. Contrary to mammalian models, this process remains largely unexplored in invertebrates. The purpose of this study was to elucidate the impact of OCM short-term alteration on the ftness and epigenome of the keystone species, Daphnia. We used maternal age at reproduction, brood size and survival rates in combination with DNA methylation sensitive comet assay to determine the efects of vitamin B12 or MTX on ftness and the epigenome. Vitamin B12 had a positive infuence on Daphnia ftness and we provide evidence demonstrating that this may be associated with an increased level of genome-wide DNA methylation. Conversely, exposing D. magna to MTX negatively infuenced the ftness of the animals and was associated with loss of global DNA methylation, translating in decreased ftness. These results highlight the potential importance of OCM in invertebrates, providing novel evidence supporting a potential role for epigenetic modifcations to the genome in D. magna environmental adaptability.