Prada-Montoya, Carlos A.

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    Phenotypic and genetic variability in the octocoral Plexaura flexuosa
    (2007-05) Prada-Montoya, Carlos A.; Yoshioka, Paul M.; College of Arts and Sciences - Sciences; Schizas, Nikolaos; Weil, Ernesto; Aponte, Nilda; Department of Marine Sciences; Almodovar, Wanda
    Clonal marine organisms exhibit high levels of morphological variation. Morphological variation may be a response to environmental factors but also they can be attributed to genetic factors. In this study, we examined the extensive morphological variation observed in the gorgonian Plexaura flexuosa (Lamouroux, 1821), a widely distributed Caribbean octocoral. We quantified differences in morphological traits in natural populations along depth profiles (shallow <5 m and deep >17 m), degree of protection to water motion and sedimentation rates (from inshore, protected and high sedimentation rates to offshore, exposed and lower sediment loads). Also, transplant experiments and genetic analysis were performed to test for possible ecophenotypic and genetic interactions. Significant differences (P<0.001) in 14 morphological traits were found among colonies inhabiting 12 locations comprising seven reefs in southwest Puerto Rico. Results from principal component analysis indicated the presence of two groups based on depth distribution, suggesting the presence of two discrete morphotypes (i.e. shallow type <5 m and deep type >17 m). A discriminant function analysis based on a priori univariate and multivariate analyses (which separated the colonies in morphotypes) correctly classified 93% of the colonies for each environment. Light, water motion and sediment transport co-varied along the depth profiles and they might influence the distribution of the two morphotypes. However, the study was not designed to separate the contribution of each variable. Reaction norms of morphological characters of colonies that were reciprocally transplanted showed gradual significant changes through the 15 months of transplantation. Sclerites of shallow water colonies became larger when transplanted to deeper environments and vice versa, but, neither of the two transplanted groups overlapped with the residents’ morphology. Genetic analysis of mitochondrial and nuclear genes suggested that such discrete morphology and non-overlapping phenotypic plasticity is correlated with the presence of two independent evolutionary lineages distributed non-randomly in shallow and deep environments. The genetic patterns found in the two sympatrically living morphs may have resulted from 1) secondary contact after populations diverged in allopatry and reproductive isolation machinery developed, 2) by divergence with gene flow through ecological specialization in sympatry or 3) by the poorly understood process of hybridization in anthozoan evolution.