CLONAL VARIATION FOR PHENOTYPIC PLASTICITY IN THE CORAL MADRACIS-MIRABILIS

Morphological plasticity is common among clonal organisms, including s cleractinian corals, yet the role of phenotypic plasticity in coral ec ology and evolution is largely unexplored. Additionally, it is unclear how much variation in plastic responses exists among individuals, pop ulations, and species, and thus how much potential there is for natura l selection to act on coral reaction norms. In the branching coral Mad racis mirabilis, corallite architecture and density, branch diameter a nd spacing, and overall aggregate morphology all vary among environmen ts. To examine the role of phenotypic plasticity in generating these p atterns, clonal replicates of five genotypes of M. mirabilis were tran splanted from each of two source populations into four treatment envir onments on the north coast of Jamaica. Flow rate, sedimentation, irrad iance, water temperature, and salinity all varied among these environm ents. DNA fingerprinting was used to ensure that the 10 transplanted g enotypes were genetically distinct. Six morphological traits (intersep ta area, septa length, columella area, corallite area, corallite spaci ng, and branch tip diameter) were measured after transplantation to de termine whether they were altered in response to environmental conditi ons. Because these traits were correlated, principal components analys is was used to define new, uncorrelated traits for analysis. Four of t he five corallite traits and branch diameter were significantly affect ed by the environment, demonstrating that morphological variation amon g environments in M. mirabilis is due in large part to phenotypic plas ticity. No difference was detected between the two source populations in the magnitude or direction of their plastic responses, but there wa s substantial variation among genotypes (genotype x environment intera ction). Many of the phenotypic changes of both populations resulted in the transplants becoming morphologically similar to resident conspeci fics in each treatment environment. Genotypes from both populations we re able to maintain similar growth rates under diverse environmental c onditions. Such morphological convergence by phenotypic plasticity may expand the ecological range of this species by enabling genotypes to tolerate spatially and temporally variable environments.