(A) Developmental stages of D. magna during early embryogenesis at 23°C as observed by GFP fluorescence in an H2B-GFP transgenic line. (B) Expression levels of Spo in siControl and siSpo embryos at 6 h assessed by qRT-PCR. Values are means. Error bars represent SD (N = 3). **p<0.01 (Student’s t-test). (C) Developmental progression and survival rate of siControl and siSpo with or without exposure to 1 μM 20-hydroxyecdysone (20E). Bars denote the developmental stages described in (A): stage 1 (white), stage 2 (blue), stage 3 (green), stage 4 (yellow), stage 5 (gray). (D) Representative images of embryos injected with siControl, siSpo, and siSpo rescued by 20E. Embryos were imaged by GFP fluorescence. Representative photographs from different stages are combined into a single image. (E) Retardation of embryo developmental progression. Compound eye (a) and naupliar eye (b) development observed at 46 h after ovulation. Scale bar, 200 μm.