Shape-shifting corals: molecular markers show morphology is evolutionarily plastic in Porites.
BACKGROUND
Corals are notoriously difficult to identify at the species-level due to few diagnostic characters and variable skeletal morphology. This 'coral species problem' is an impediment to understanding the evolution and biodiversity of this important and threatened group of organisms. We examined the evolution of the nuclear ribosomal internal transcribed spacer (ITS) and mitochondrial markers (COI, putative control region) in Porites, one of the most taxonomically challenging and ecologically important genera of reef-building corals.


RESULTS
Nuclear and mitochondrial markers were congruent, clearly resolving many traditionally recognized species; however, branching and mounding varieties were genetically indistinguishable within at least two clades, and specimens matching the description of 'Porites lutea' sorted into three genetically divergent groups. Corallite-level features were generally concordant with genetic groups, although hyper-variability in one group (Clade I) overlapped and obscured several others, and Synarea (previously thought to be a separate subgenus) was closely related to congeners despite its unique morphology. Scanning electron microscopy revealed subtle differences between genetic groups that may have been overlooked previously as taxonomic characters.


CONCLUSIONS
This study demonstrates that the coral skeleton can be remarkably evolutionarily plastic, which may explain some taxonomic difficulties, and obscure underlying patterns of endemism and diversity.
Forsman
Zac H
ZH
Hawaii Institute of Marine Biology, Kaneohe, HI 96744, USA. zac@hawaii.edu
Barshis
Daniel J
DJ
Hunter
Cynthia L
CL
Toonen
Robert J
RJ
D000818:Animals; D037421:Anthozoa / Q000033:anatomy & histology / Q000145:classification / Q000235:genetics*; D001499:Bayes Theorem; D044822:Biodiversity; D002467:Cell Nucleus / Q000235:genetics; D004272:DNA, Mitochondrial / Q000235:genetics; D021903:DNA, Ribosomal Spacer / Q000235:genetics; D019143:Evolution, Molecular; D005819:Genetic Markers; D008928:Mitochondria / Q000235:genetics; D010802:Phylogeny; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA
D004272:DNA, Mitochondrial; D021903:DNA, Ribosomal Spacer; D005819:Genetic Markers