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MODULAR VARIATION AND PHENOTYPIC PLASTICITY IN THE GORGONIAN CORAL PSEUDOPTEROGORGIA BIPINNATA ALONG THE WESTERN CARIBBEAN

Juan A. Sánchez, D. Dorado and N. Manrique.
Universidad de Los Andes, Colombia
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One of the most intriguing aspects of evolution is whether habitat-induced phenotypic variation can lead to genetically fixed morphotypes. The gorgonian coral Pseudopterogorgia bipinnata (Gorgorniidae: Octocorallia) provides a great opportunity to explore phenotypic plasticity and morphological variation in a coral reef organism. We studied the variation of different morphological traits including the different types of microscopic sclerites (0.1-0.2 mm of length variation), polyp aperture and spacing (1-20 mm), and branches and internodes (1-20 mm), which are all repetitive modules throughout the colony. In addition, we studied the genetic variation of the Internal Transcribed Spacer 2 (ITS2, rDNA) using a combined approach with Denaturing Gradient Gel Electrophoresis (DGGE) and DNA sequencing of the different copies found at each individual colony. We examined colonies from Carrie Bow Cay (Belize), Bocas del Toro (Panama) and Cartagena (Colombia), which included most reef habitats (1-35 m in depth) and several morphotypes. Only one feature did not change at all across habitats despite an order of magnitude difference in other features such as branch length and lesser, but significant, differences in the remaining traits. We distinguished three P. bipinnata morphotypes: shallow exposed, shallow to mid-depth (moderately exposed) and low water motion in deep-water (<20 m) morphotypes, which were independent of genetic variation. The three phenotypes did not exhibit clines and were seldom seeing side-to-side sharing the same environment at overlapping zones. Ecotypes can make some traits exhibit phenotypic plasticity but are not so extreme to make these traits fixed in the species genome. In need of further screening, genetic assimilation can be a viable event for octocorals, where habitat seems to be a conditioning factor for niche separation.