Materials and Methods
Spawning, larval rearing, settlement and symbiont infection
Gravid adult corals of the species Acropora spathulata were collected from one reef in the far north of the Great Barrier Reef (Tijou, far northern GBR; 13°10’44.0”S, 143°56’54.6”E, permit G16/38488.1) and one reef in the central GBR (Backnumbers, central GBR; 18°30’49.8”S, 147°09’10.7”E, permit G12/35236.1) and brought back to the National Sea Simulator (SeaSim) for coral spawning in November 2017 as outlined in (Quigley et al., 2020). Briefly, on the night of spawning the separated eggs and sperm from three far northern colonies were mixed with those of three central colonies, resulting in larvae from 30 distinct familial crosses that were raised in 27.5°C ultrafiltered, flow-through seawater (see Table 1 for pedigree and parental colony designations). Only five families were available at the time of larval settlement and used to produce recruits (hereafter referred to as juveniles given measurements were taken after 70 days of development). Here we focus on those five familial crosses sequenced at both the larval stage (27.5°C) and the juvenile stage (27.5°C and 31°C). These crosses include three produced from two parents sourced from the warm far northern reef (WW1, WW2, WW3), one cross with a warm dam and cool sire (WC) and one with a cool dam and warm sire (CW). Aposymbiotic juveniles were infected with Symbiodinium tridacnidorum ,Cladocopium goreaui , and Durusdinium trenchii with cultured material obtained from the AIMS Symbiont Culture Facility (further details in Quigley et al., 2020). Full details of the collection, environmental parameters of each location, permits, spawning, larval and juvenile rearing, and symbiosis establishment can be found in Quigley et al., 2020. Briefly, symbiosis establishment in coral juveniles was performed by adding 1x105 ml-1of one of the three cultured symbiont strains separately to each juvenile tank (n = 3 replicate tanks per culture), suspending the flow to allow for contact between corals and symbionts, and repeating one further time until infection was confirmed with microscopy.