Fig. 1. Conceptual diagrams and experimental design.

a Effectiveness of selective breeding in shifting heat tolerance distributions (bell curves) of offspring from parents with low (red) or high (blue) heat tolerance is dependent on narrow-sense heritability (h²). Dashed lines represent the mean of low heat tolerant parental colonies (red), the population (black) and high tolerant colonies (blue). b Corals in the source population were located on the reef and (c) selectively bred offspring (F1) colonies were reared in common garden nurseries. d Timelines are given for short- (left) and long-term (right) heat stress tolerance, showing dates of parental heat stress selection assays, selective breeding, nursery rearing, and adult offspring heat stress assays. Parental colonies were obtained from the same source population for both selective breeding efforts (2018 and 2019).