Host genetics and Symbiodinium D diversity in a stress-tolerant scleractinian coral, Oulastrea crispata, in the West Pacific

Determination of the genetic diversity and structure of coral populations across their biogeographic range must include the investigation of the coral host and its associated Symbiodinium. We examined the genetic similarity of the stress-tolerant coral Oulastrea crispata and the diversity of Symbiodinium D across part of their geographic distribution, which ranges across 5800 km in the West Pacific from tropical Thailand (similar to 7 degrees N) to the outlying regions of temperate Japan (36 degrees N). F-ST-statistics and AMOVA of directly sequenced coral ribosomal internal transcribed spacer (ITS) DNA sequences showed a high genetic homogeneity between temperate and subtropical populations, but showed a significant difference between temperate and subtropical populations and their tropical counterparts. Denaturing gradient gel electrophoresis (DGGE) of ITS DNA sequences identified 4 major O. crispata-associated Symbiodinium D types: D8, D8-12, D12-13, and D15; these were found in the regions extending from tropical Thailand towards the high latitude regions of Japan. F-ST-statistics and AMOVA of Symbiodinium ITS showed significant differences between tropical, subtropical, and temperate regions, with the D8 and D8-12 dominant in the tropical and subtropical regions, the D12-13 endemic in the subtropical northern South China Sea, and D15 restricted to the high-latitudinal outlying coral communities. Consistent variation in environmental factors, such as temperature and light, may have driven the regional specific divergence of the Symbiodinium D types, suggesting that habitat-specific Symbiodinium types can assist O. crispata in acclimating to the environmental fluctuations found in the marginal range of coral distribution.