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Peer-reviewedCC BY 4.0Ecology and Evolution

Formal Description of Cladocopium proximale sp. nov., a Coral Photosymbiont From the C1 Radiation

  • Giorgio Terzi1
  • Madeleine J. H. van Oppen2,3
  • Davide Seveso1,4
  • Matthew R. Nitschke2,5
5 affiliations
  1. 1Department of Earth and Environmental Sciences (DISAT) University of Milano—Bicocca Milano Italy
  2. 2Australian Institute of Marine Science Townsville Queensland Australia
  3. 3School of BioSciences The University of Melbourne Parkville Victoria Australia
  4. 4MaRHE Center (Marine Research and High Education Centre) Magoodhoo Island Faafu Atoll Maldives
  5. 5School of Biological Sciences Victoria University of Wellington Wellington New Zealand
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Abstract

Coral reefs are among the most biodiverse ecosystems on Earth and rely on endosymbiosis with Symbiodiniaceae, a diverse family of dinoflagellates essential for coral nutrition and which also play an important role in thermal tolerance. Despite their ecological importance, resolving species boundaries within Symbiodiniaceae remains challenging, partly due to limited phylogenetic signal in commonly used genetic markers and the absence of broadly accepted criteria for species delimitation. Refining taxonomic resolution is therefore critical for understanding symbiont diversity, distributions, and evolutionary relationships. In this study, we delimit two closely related Cladocopium species using a meta‐haplotype framework applied to two hypervariable loci—the ITS2 region and the psbA non‐coding region (psbA ncr ). Slowly evolving markers failed to differentiate Cladocopium proximale (SCF049; described here) from its sister species C. proliferum . In contrast, consistent genetic differences between the two taxa were detected across both hypervariable regions. Together with morphological differences, these results support the recognition of C. proximale and C. proliferum as distinct species. Our results highlight the value of combining multiple hypervariable markers to improve taxonomic accuracy in Symbiodiniaceae, providing a stronger basis for understanding how symbiont diversity and ecological differentiation may influence coral resilience and responses to environmental change. More broadly, closely related Symbiodiniaceae such as these provide important systems for examining speciation processes, including potential ecological differentiation and reproductive compatibility.

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Cite

BibTeXRIS
BibTeX
@article{terzi2026formal,
  title = {{Formal Description of Cladocopium proximale sp. nov., a Coral Photosymbiont From the C1 Radiation}},
  author = {Giorgio Terzi and Madeleine J. H. van Oppen and Davide Seveso and Matthew R. Nitschke},
  journal = {Ecology and Evolution},
  year = {2026},
  month = nov,
  doi = {10.1002/ece3.74569},
  url = {https://onlinelibrary.wiley.com/doi/10.1002/ece3.74569},
  note = {CC BY 4.0},
}
RIS
TY  - JOUR
TI  - Formal Description of Cladocopium proximale sp. nov., a Coral Photosymbiont From the C1 Radiation
AU  - Giorgio Terzi
AU  - Madeleine J. H. van Oppen
AU  - Davide Seveso
AU  - Matthew R. Nitschke
PY  - 2026
DA  - 2026/11/05
JO  - Ecology and Evolution
DO  - 10.1002/ece3.74569
UR  - https://onlinelibrary.wiley.com/doi/10.1002/ece3.74569
AB  - Coral reefs are among the most biodiverse ecosystems on Earth and rely on endosymbiosis with Symbiodiniaceae, a diverse family of dinoflagellates essential for coral nutrition and which also play an important role in thermal tolerance. Despite their ecological importance, resolving species boundaries within Symbiodiniaceae remains challenging, partly due to limited phylogenetic signal in commonly used genetic markers and the absence of broadly accepted criteria for species delimitation. Refining taxonomic resolution is therefore critical for understanding symbiont diversity, distributions, and evolutionary relationships. In this study, we delimit two closely related Cladocopium species using a meta‐haplotype framework applied to two hypervariable loci—the ITS2 region and the psbA non‐coding region (psbA ncr ). Slowly evolving markers failed to differentiate Cladocopium proximale (SCF049; described here) from its sister species C. proliferum . In contrast, consistent genetic differences between the two taxa were detected across both hypervariable regions. Together with morphological differences, these results support the recognition of C. proximale and C. proliferum as distinct species. Our results highlight the value of combining multiple hypervariable markers to improve taxonomic accuracy in Symbiodiniaceae, providing a stronger basis for understanding how symbiont diversity and ecological differentiation may influence coral resilience and responses to environmental change. More broadly, closely related Symbiodiniaceae such as these provide important systems for examining speciation processes, including potential ecological differentiation and reproductive compatibility.
SN  - 2045-7758
SN  - 2045-7758
ER  -