Figure 1. Impact of thermal stress on the development of Ciona intestinalis types (A,B).

(A–E) Impact of short-term exposure to heat shock. Control embryos were cultured at 17 °C. Others were treated at 27 °C for 1 h at the neurula stage, the minimum condition to observe the differences in buffering of thermal stress between types A and B (Supplementary Fig. S1), before returning to 17 °C as schematically illustrated in (A). Outcomes vary from normal development (B) to truncation of the tail (C) to more severe effects on development resulting in a failure to hatch (D). Scale bar: 100 μm. (E) Comparison of the normal proportion of development (the proportion of normal development in treated embryos relative to the proportion in controls) after heat shock in different genotypes. (F,G) Impact of long-term exposure at moderately increased temperature. Early cleavage embryos (4–8 cell stage) were reared at 24 °C and control embryos at 17 °C until hatching as shown schematically in (F). (G) Comparisons of normal proportion after heat shock in different genotypes. The bottom and top lines of the boxes indicate 25^th and 75^th percentiles, and the horizontal lines how median of each data. The vertical lines show either the maximum value or 1.5 times of the interquartile range of the data, whichever the smaller. In both types of treatment, ANOVA rejected the null hypothesis that the impact of thermal stress does not depend on the genotypes by ***P < 10⁻¹⁵. AA, type A conspecific cross; BB, type B conspecific cross; AB, hybrids using type A egg and type B sperm; BA, hybrids using type B eggs and type A sperm.