Cryptic Species: A Mismatch between Genetics and Morphology in Millepora

Millepore morphology is highly variable and shows signs of phenotypic plasticity. Two species of Millepora are present around the islands of the Bahamas: one exhibiting a strong, blade-like structure, Millepora complanata, and the other having a delicate branch-like structure, Millepora alcicornis. The phylogenetic relationship of these corals has been under considerable debate for many years. The existence of a range of intermediate growth forms exhibiting characteristics of both recognized species has led to the re-examination of this species complex. Several methods were employed to examine the taxonomic relationship including ecological abundance surveys, morphological thin-section analysis, and sequencing of rDNA internal transcribed spacer (ITS) regions. Abundance surveys showed a demarcation of growth forms by depth at two sites but an intermingling of growth forms at a third site. Morphometric analysis resulted in discrimination between M. alcicornis, M. complanata and the intermediate growth forms. However, rDNA sequence differences revealed the presence of two distinct clades, each containing members of the two currently recognized species as well as intermediate growth forms. The sequence analysis suggests the presence of two, phenotypically plastic cryptic species. Although limited in scope, our results indicate that caution should be exercised when describing species based on morphology alone and that multiple characters, including genetic information, should be used when describing species relationships.