Polyp bail-out induction and RNA sampling for transcriptomic
analysis (Experiment I)
To examine the transcriptomic response during initiation of polyp
bail-out, we collected RNA samples at 12-hour intervals during induction
of the bail-out response in P. acuta , using a hyperosmotic
treatment modified from Shapiro et al. (2016). One day prior to the
experiments, six coral fragments from a mother colony were clipped off
and randomly placed in two 5-L indoor experimental tanks. Artificial
seawater (Kaisuimaren, Japan) at 35‰ salinity was prepared in these
tanks (three in the treatment group and three in the control group).
Light intensity was provided at 300 μmol photons m-2s-1 with a 12-hour day-night cycle. Tank temperature
was allowed to fluctuate daily in the range of 24 – 26°C. For the
treatment group, high-salinity artificial seawater (48‰) was pumped into
the experimental tank at a constant rate of 4 mL/min to create
hyperosmotic conditions, while salinity remained unchanged for the
control group. Since partial polyp detachment (an indicator of onset of
polyp bail-out) was observed in the treatment group at 24 h, we
collected both undetached polyps and detached polyps (10 – 15
polyps/sample) separately. The same experiment was repeated three times
on different P. acuta colonies, with at least one month between
experiments (N = 3).