a, Schematic of an adult C. elegans showing the location of the syncytial gonad and expected membrane partition retraction phenotype in control and cyk-4(ts) worms on upshift to 26 °C. b, Representative images from whole-animal upshift experiments with control and cyk-4(ts) mutants. Time is in minutes after temperature upshift. Orange arrows indicate membrane partition retraction. c, Schematic (left) and quantification (right) of membrane partition length before and after thermal upshift after whole-animal upshift to the restrictive temperature. Control: N = 8 worms, cyk-4(ts) at 16 °C: N = 7 worms, and cyk-4(ts) at 26 °C: N = 5 worms; with four partitions measured per worm. Unpaired two-tailed t-test; n.s., no significance, P > 0.05; *P ≤ 0.05; **P ≤ 0.01; ****P ≤ 0.0001. Error bars, mean +/− s.d.; see Supplementary Table 1 for statistical analysis. Scale bar, 10 µm.