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.