Variation in Symbiodinium ITS2 sequence assemblages among coral colonies

Area of Science:

• Marine Biology
• Symbiosis Research
• Genetics and Genomics

Background:

• Endosymbiotic dinoflagellates in the genus Symbiodinium are crucial for scleractinian coral health and environmental tolerance.
• The genetic diversity of Symbiodinium is known, but its fine-scale spatial partitioning within coral species remains understudied.
• Understanding Symbiodinium distribution is key to assessing coral population resilience and local adaptation.

Purpose of the Study:

• To investigate the partitioning of Symbiodinium diversity across spatial scales within the coral Montipora capitata.
• To characterize Symbiodinium ITS2 sequence assemblages within individual coral colonies.
• To evaluate the implications of Symbiodinium diversity for coral adaptation and species identification.

Main Methods:

• Sampling of 52 Montipora capitata colonies across Kāne'ohe Bay, Hawai'i, using a nested design (Colony(Site(Region))).
• Analysis of Symbiodinium ITS2 (Internal Transcribed Spacer 2) sequence assemblages from coral samples.
• In-depth sequencing of 35–55 clones per colony for six selected M. capitata colonies to confirm diversity patterns.

Main Results:

• A significant diversity of Symbiodinium ITS2 sequences was detected.
• The majority of sequence variation partitioned at the level of the individual coral colony.
• Each analyzed coral colony hosted a distinct assemblage of Symbiodinium, with significant quantitative differences.

Conclusions:

• Symbiodinium ITS2 sequence assemblages exhibit high variability within individual Montipora capitata colonies.
• This intra-colony diversity challenges the interpretation of multi-copy and intra-genomic markers for Symbiodinium identification.
• The findings necessitate a re-evaluation of the utility and biological relevance of Symbiodinium ITS2 genotyping for species assignment.