Speciation in Fire Corals: What Constitutes a Species?

April 18th, 2009

Two morphologies of Millepora, currently classified as separate species, exist off the coast of the Bahamas. Millepora complanata is found primarily in shallow waters, possessing wide, smooth branches whereas Millepora alcicornis is found primarily in deeper waters, possessing thinner, knobby branches. Upon discovery of colonies that contain intermediate morphologies, the question arose as to whether these different morphologies represent different species or whether the differences result from ecophenotypic plasticity. Reef survey analyses have revealed the appearance of both the branching and blade morphs at the same depth at some reef locations. The occurrence of these forms in mutual proximity supports the contention that morphologic variation of this genus is not primarily a response of a single species to environmental differences and suggests that they possess distinct genetic differences.

To better understand the phylogenetic relationship, DNA was isolated from samples of each morphology and the non-coding internal transcribed spacer (ITS) regions of rDNA were examined. Because the ITS regions tend not to be highly conserved, they are good indicators of species-level differentiation. DNA sequence analysis showed specific differences in nucleotide sequence between Milleporid specimens at five identical nucleotide positions for all samples. Full-length rDNA sequences (36) were entered into MEGA and a maximum likelihood tree was created. The phylogenetic tree showed that the coral separated into two distinct clades. Each clade is independent of depth, reef location or morphology. This suggests that Milleporids may be reproductively isolated cryptic species, and that traditional features used for classification may be of little value.

Charles Hay, ’10 Buckingham, IA
Majors: Special Studies
Arno Reichel, ’09 Dalton, IL
Major: Biology
Benjamin Greenstein
Cornell College
Robert Black
Cornell College
Creig Tepper
Cornell College

Sponsor: Craig Tepper

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