AN INVESTIGATION OF POSSIBLE STOCK STRUCTURE IN PECTEN-MAXIMUS (L.) USING MULTIVARIATE MORPHOMETRICS, ALLOZYME ELECTROPHORESIS AND MITOCHONDRIAL-DNA POLYMERASE-CHAIN-REACTION RESTRICTION-FRAGMENT-LENGTH-POLYMORPHISM

Population heterogeneity in the scallop Pecten maximus (L.) has been s tudied by multivariate morphometrics and allozyme electrophoresis and compared with data from a mitochondrial DNA polymerase chain reaction- restriction fragment length polymorphism method. Principal component a nalysis applied to shell measurements revealed some variation in shape , with significant differences in aspects of morphology detectable amo ng populations. Trends suggestive of morphological distinctness of a p opulation or populations were difficult to uncover; however, animals f rom Brest and La Trinite (Brittany, France) were consistently differen t from other P. maximus populations on the basis of principal componen t 1, largely attributable to hinge length. St. Brieuc Bay P. maximus, which are known to exhibit differences in reproductive cycle from neig hboring populations and thus are thought to be reproductively isolated , could not be separated on the basis of shell shape, although limited differences in the number of ribs in comparison to other populations are evident. Allele frequencies at seven loci assessed by allozyme ele ctrophoresis were essentially homogeneous throughout the sample range in accord with previous studies and provided little evidence for popul ation subdivision, although allele frequencies at the Odh locus provid ed some evidence that two Scottish populations were genetically differ entiated. This contrasted with both the morphological differences dete cted for two Brittany populations and with data from the mitochondrial DNA, which indicated that the P. maximus population from the semiencl osed sea lough Mulroy Bay, fire, was genetically differentiated from a ny other population sampled on the basis of sequence divergence values .