Contour analysis in subtidal and intertidal populations of the mussel Mytilus edulis platensis d’ Orbigny, 1842

YUVERO, MARÍA CELESTE; LOMOVASKY, B.; GIMÉNEZ, J.

Congreso; THE EUROPEAN CONGRESS OF MALACOLOGICAL SOCIETIES 2021; 2021

Outline shape in bivalves is a key character that provides information on life habits, and is relatedwith endogenous (genetic and physiological) and exogenous (biotic and abiotic) factors. Themussel Mytilus edulis platensis d’ Orbigny, 1842 presents a wide distribution from Rio Grandedo Sul (32° 2´S; 52°5´W), southern Brazil to Santa Cruz (50° 1’S; 68° 31’W), Argentina. The aimof this study was to compare the subtidal and intertidal populations of M. edulis platensis throughcontour morphology; we hypothesize an association between shell morphology and habitat dueto habitat-specific constraints. The subtidal samples were obtained on board the ARA PuertoDeseado, at 35 meters deep, in August 2012 at the Litoral Bonaerense (36º 53’ S; 56º 20’ W)(n=37); the intertidal samples were collected in August 2019 in Villa Gesell (37° 15´S; 56° 57´W),Buenos Aires province, Argentina (n=33). Left valves were digitized with a digital camera. Westudied the overall shell shape with an Elliptic Fourier Analysis (EFA) of the closed contour, withseven harmonics, and carried out a Principal Component Analysis (PCA). Significant differencesbetween contours were tested with a MANOVA. The PCA allowed us to discriminate twomorphotypes through the outline data. The first principal component (PC1) accounted for 75.59%of the variability, while the second principal component (PC2) determined 12.93%. We associatethe PC1 to differences in the width; globose shapes representing intertidal individuals and narrowshapes related to the subtidal. Differences along the PC2 were related to the angle of ventraldisplacement of the umbo, evident in the subtidal specimens. Statistically significant differencesbetween contours were defined (MANOVA: Wilk’s lambda= 0.31, F2, 69= 78.37, P < 0.001). Allthese results suggest that M.edulis platensis has developed two ecomorphs with distinctmorphological responses to physically stressful conditions registered in the intertidal, as opposedto lower physical stress in the subtidal habitats