Fig. 1.

Study species, experimental crosses, and fertilization rates. (A) Study species: elkhorn coral A. palmata. (B) Map of the Caribbean Sea and genetically distinct A. palmata populations. Circles indicate the locations of gamete collection and cryopreservation of sperm samples from Florida (FL, n = 2 sires), Puerto Rico (PR, n = 5 sires), and Curaçao (CUR, n = 6 sires). FT sperm was cryopreserved in the year listed and thawed immediately before use in in vitro fertilization experiments with freshly collected eggs from Curaçao (n = 5 dams). Freshly collected sperm from Curaçao (n = 4 or 5 sires, depending on spawning night) was used for comparison. (C) Summary of in vitro crosses conducted to test the feasibility of AGF in A. palmata. (D) Mean fertilization success for A. palmata eggs from five donor colonies (dams) when mixed with each of the four sperm pools or a no-sperm control (n = 1 to 9 containers per dam × sperm pool cross; replicate egg containers were preferentially assigned to the three FT crosses and the two interpopulation (AGF) crosses based on the lower fertilization rates expected from FT sperm and the higher conservation value of the AGF crosses). Sperm concentration and handling details are summarized in SI Appendix, Table S2. For all FT treatments, fertilization was attempted at two different sperm concentrations (n = 1 to 6 containers per concentration per cross); this bracketing approach during gamete handling was employed to maximize the overall chance of achieving fertilization using cryopreserved material (SI Appendix, Tables S2 and S3 for details).