Data of fitness effects of environmental stressors on Daphnia magna over multiple generations. Ages of first and second reproduction, and sizes of first and second brood were measured and used to calculate replacement rate. This data is part of a study on whole-genome bisulphate sequencing on individual Daphnia magna to assess whether environmentally-induced DNA methylation can persist for up to four generations.

A stock of Daphnia magna was sourced from Lake Bysjön (surface area 10 ha, 55°40'32"N 13°32'42"E) in Southern Sweden. Single clonal lines were kept under laboratory conditions (Radersma et al., 2018) and allowed to reproduce asexually for 12 months before the onset of the experiment. All experiments in this study used a single clone to minimize any genetic effects. Individual Daphnia of the generation F0 were exposed to environmental stressors or a control treatment from birth to first reproduction. As stressors we used 5-azacytidine, microcystin, high temperature and zinc (for more details such as concentrations see the main publication). Following the first brood, all individuals of the F0 generation were maintained under control conditions. We propagated these lines down to generation F4 by isolating five offspring from the second brood in each generation and keeping them under control conditions. Subsequent generations (F2, F3 and F4) did not encounter the stressors. This experiment was performed three times simultaneously (T1, T2 and T3), to account for potential incompleteness due to the extinction of maternal lines, and the most complete experiment for each stressor was subjected to further analyses. To assess how the stressor treatments affect the lifetime reproductive success of exposed individuals and their descendants, we collected the age of first and second reproduction (in days) and the sizes of the first and second brood for all individuals of the selected experiment. We estimated fitness by calculating, for each individual, the intrinsic rate of population increase r with a univariate root finding algorithm (uniroot in R) using the Euler equation.