Standard Presentation (15 mins) Australian Marine Sciences Association 2022

Cryptic diversity and co-structuring of genetic variation in Acropora tenuis and its endosymbionts across the Great Barrier Reef (#26)

Ambrocio Melvin A Matias 1 2 , Iva Popovic 1 , Joshua A Thia 3 , Ira R Cooke 4 , Gergely Torda 5 , Vimoksalehi Lukoschek 5 6 , Line K Bay 7 , Sun W Kim 1 , Cynthia Riginos 1
  1. School of Biological Sciences, University of Queensland, St. Lucia, QLD, Australia
  2. Institute of Biology, University of the Philippines Diliman, Quezon City, Philippines
  3. Bio21 Institute, School of BioSciences, The University of Melbourne, Parkville, VIC, Australia
  4. College of Public Health, Medical and Veterinary Sciences, James Cook University, Townsville, QLD, Australia
  5. ARC Centre of Excellence for Coral Reef Studies, James Cook University, Townsville, QLD, Australia
  6. Gold Coast University Hospital, Queensland Health, Southport, QLD, Australia
  7. Australian Institute of Marine Science, James Cook University, Townsville, QLD, Australia

Genomic studies are uncovering extensive cryptic diversity within reef-building corals, suggesting that evolutionarily and ecologically relevant diversity is highly underestimated in the very organisms that structure coral reefs. Despite the essential ecological role of reef-building corals and urgent concerns about how populations will evolve in the Anthropocene, the processes shaping coral diversity are poorly understood. Here, we use low-coverage genome-wide sequencing of the reef-building coral Acropora tenuis (n=463) and associated endosymbiotic algae to investigate cryptic species diversity across the GBR. We discover three distinct and sympatric genetic clusters of coral hosts, whose distributions appear associated with latitude and inshore-offshore reef position. Demographic modelling suggests that the divergence history of three distinct host taxa ranges from 0.5 – 1.5 million years ago, preceding the GBR’s formation, and has been characterised by low ongoing inter-taxon gene flow, consistent with occasional hybridisation and introgression typifying coral evolution. Endosymbiont plastid diversity is not strongly associated with host identity but varies with reef location relative to shore, possibly reflecting local selective pressures maintaining coral holobiont differentiation. The strong influence of environment (but not host identity) on endosymbiont community composition supports the notion that endosymbiont diversity enables corals to match their habitat and may contribute to coral adaptation under future environmental change.