Evolutionary genetics of Metridium senile. II. Geographic patterns of allozyme variation

Electrophoretic surveys have demonstrated that populations of the sea anemone Metridium senile along the northeast coast of the United States are polymorphic at four enzyme loci. Phosphoglucose isomerase (PGI) has two alleles in most populations, phosphoglucomutase (PGM) has three alleles, and two leucine aminopeptidase loci have two common alleles each. Phosphoglucose isomerase displays clinial variation and an apparent association with environmental temperature. Phosphoglucomutase shows clinial variation north of Cape Cod for two of the three alleles, while the two leucine aminopeptidase loci are not clinial. All loci show a great deal of variation in populations on Cape Cod, but there is no apparent systematic pattern of this variation. Temperature may be a selective agent in the maintenance of the PGI and PGM clines, although other possibilities cannot presently be completely excluded.