Study organisms
As previously outlined in Issa et al. (2020), ephippia containing resting eggs resulting from sexual reproduction of D. magna were collected in November 2014, in a pond at Værøy Island (1.0 ha, 67.687°N 12.672°E), northern Norway. Ephippial eggs were hatched in the laboratory and propagated clonally. For the current experiment, juveniles of a single clone (clone 49) of D. magna were asexually propagated for ten successive generations prior to use. A maximum of 30 individuals of D. magna were cultured in 2.5 L aquaria at 20 °C in a modified “Aachener Daphnien Medium” (ADaM) (Klüttgen et al., 1994, SeO2 concentration reduced by 50%), under long photoperiods (16h L: 8h D) using white fluorescent lamps. The medium was exchanged weekly and the animals were fed three times a week with Shellfish Diet 1800® (Reed mariculture Inc.) at a final concentration of 3.2 × 105 cells/mL.