Coral Reefs

, Volume 22, Issue 2, pp 155–166 | Cite as

Species boundaries within the Acropora humilis species group (Cnidaria; Scleractinia): a morphological and molecular interpretation of evolution

  • J. K. WolstenholmeEmail author
  • C. C. Wallace
  • C. A. Chen


Species boundaries remain unresolved in many scleractinian corals. In this study, we examine evolutionary boundaries of species in the Acropora humilis species group. Five morphologically discrete units are recognized using principal components and hierarchical cluster analyses of quantitative and qualitative characters, respectively. Maximum parsimony and likelihood analyses of partial 28S rDNA sequences suggest that these morphological units diverged to form two evolutionarily distinct lineages, with A. humilis and A. gemmifera in one lineage and A. digitifera and two morphological types of A. monticulosa in the other. Low levels of sequence divergence but distinct morphologies of A. humilis and A. gemmifera within the former lineage suggest recent divergence or ongoing hybridization between these species. Substantially higher levels of divergence within and between A. digitifera and A. monticulosa suggest a more ancient divergence between these species, with sequence types being shared through occasional introgression without disrupting morphological boundaries. These results suggest that morphology has evolved more rapidly than the 28S rDNA marker, and demonstrate the utility of using morphological and molecular characters as complementary tools for interpreting species boundaries in corals.


Acropora Morphology 28S rDNA Species boundaries 



We thank T. Hughes, N. Daschbach, A. Green, and P. Craig for organizing field logistics and E. Dinsdale, M.-J. Boyle, and P. Craig for field assistance; J. Wright for photographing branch samples; and B. Radford, S. Klanten, and students at the Institute of Zoology, Academia Sinica, for laboratory support. T. Hughes, L. van Herwerden, A. Baird, P. Muir, and two anonymous reviewers provided useful comments on the manuscript. This study was funded by grants to J. Wolstenholme from the Australian Coral Reef Society and James Cook University, an ARC grant to T. Hughes, and an NSC grant and internal funding from Academia Sinica to C.A. Chen.


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Copyright information

© Springer-Verlag 2003

Authors and Affiliations

  • J. K. Wolstenholme
    • 1
    • 2
    Email author
  • C. C. Wallace
    • 2
  • C. A. Chen
    • 3
  1. 1.Department of Marine Biology and AquacultureJames Cook UniversityTownsville Australia
  2. 2.Museum of Tropical QueenslandTownsville Australia
  3. 3.Institute of ZoologyNankangTaiwan

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