SHELL SHAPE VARIATION ALONG THE LATITUDINAL RANGE OF THE CHILEAN BLUE MUSSEL MYTILUS CHILENSIS (HUPE 1854)

Shell shape variation in the Chilean blue mussel Mytilus chilensis was examined in eight populations spread over 1,800 km in the southeastern Pacific. The shell outlines were assessed using elliptic Fourier analysis. MANOVA on Fourier coefficients showed a highly significant morphological variation between eight populations studied in the latitudinal gradient. First canonical axis was associated with convexity of ventral edge and umbo shape, while the second axis was associated with shell elongation. Genetic differentiation has been previous described, but morphological and genetic patterns were marginally congruent. Geographic distance had a stronger effect on morphology than genetics. Shape changes were correlated with geographical distances among populations and the second canonical axis (elongation) was correlated with latitudinal clinal variation, probably associated with the salinity gradient at SE Pacific.