Fig. 1

Sampling and experimental outline. a The adult H. roretzi used in this study. White and red arrows indicate the oral and atrial siphon, respectively. b The ascidian adult without tunic. c-f The stools and animals with starvation for 0, 2, 4, and 6 days, respectively. The red arrows indicate the stool inside the gut. Before starvation (Day 0), the stools are black, strip-shaped and curved (c). After starvation for 2 days (Day 2), the stool become thinner and fewer (d). After starvation for 4 days (Day 4), the stool becomes much thinner (e). After starvation for 6 days (Day 6), the stool becomes white and sticky (f). g The outlines of the sampling. Animals are starved for 0, 2, 4, and 6 days in January, April, July and October, respectively. The stools inside the gut and the seawater in the sampling locations are used for 16S rRNA gene sequencing. The stool samples in January are also utilized for metagenomic sequencing and metabolomics analysis, respectively. The tissues of the corresponding animals, which are sampled in January are used for RNA-Seq and metabolomics analysis