Genotypic variation influences reproductive success and thermal stress tolerance in the reef building coral, Acropora palmata
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The branching coral Acropora palmata is a foundation species of Caribbean reefs that has been decimated in recent decades by anthropogenic and natural stressors. Declines in population density and genotypic diversity likely reduce successful sexual reproduction in this self-incompatible hermaphrodite and might impede recovery. We investigated variation among genotypes in larval development under thermally stressful conditions. Six two-parent crosses and three four-parent batches were reared under three temperatures and sampled over time. Fertilization rates differed widely with two-parent crosses having lower fertilization rates (5–56 %, mean 22 % ± 22 SD) than batches (from 31 to 87 %, mean 59 % ± 28 SD). Parentage analysis of larvae in batch cultures showed differences in gamete compatibility among parents, coinciding with significant variation in both sperm morphology and egg size. While all larval batches developed more rapidly at increased water temperatures, rate of progression through developmental stages varied among batches, as did swimming speed. Together, these results indicate that loss of genotypic diversity exacerbates already severe limitations in sexual reproductive success of A. palmata. Nevertheless, surviving parental genotypes produce larvae that do vary in their phenotypic response to thermal stress, with implications for adaptation, larval dispersal and population connectivity in the face of warming sea surface temperatures.
KeywordsGenotype by environment interaction Climate change Larval development Compatibility Sperm morphology Egg provisioning
Thanks to SECORE for their invaluable help and guidance over the duration of this project, especially D. Peterson, M. Brittsan, N. Ireland, A. Marshall, B. Snowden, B. Christie, and M. Hagedorn. Steve Tamar and the Surf Rider Foundation, Puerto Rico chapter helped with logistics and sample collection. We are grateful to K. McAndrew and A. Wing for help with sperm morphology measurements. Thanks to M. Miller for reviewing a draft of the manuscript. Spawning activities and sample collections were conducted under DNER permit numbers 06-IC-027/08-CIC-001. Support was provided by National Science Foundation grant OCE 0825979 and the NOAA Coral Reef Conservation Program to IB.
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