Genetic Studies on the Pacific Abalone—IV: Thermostability Difference among Phosphoglucomutase Variants

Electrophoretic analysis of shell-muscle extracts from the Pacific abalone, Haliotis discus hannai Ino, indicated polymorphism with the autosomal five codominant alleles at phosphoglucomutase (Pgm) locus. The locus in the species appeared to be homologous to that in H. discus Reeve and the hybrids between the two varieties. In H. discus hannai, allele frequency difference was seen between the samples collected from Yuki, Tokushima Prefecture and the other localities: Okushiri in Hokkaido, Oga in Akita Prefecture, and Sanriku in Iwate Prefecture. Heating experiments of either tissue extracts before electrophoresis or gel after electrophoresis under the conditions of 55°C for 12 min disclosed thermostability differences, called heat-sensitive and heat-resistant types, within each electrophoretic allozyme at Pgm locus. The thermostability determinant locus appeared to reside at the Pgm structural locus. A greater frequency of occurrence of heat-sensitive allele in the samples of H. discus hannai from colder waters than warm water and a higher frequency of heat-sensitive allele in H. discus, the warm water animal, than in H. discus hannai, the cold water animal, in the samples from Oga, Akita Prefecture, which is believed to be near the northern extremity of habitats of H. discus on the coast of Japan Sea, thus strongly suggested an existence of differential viabilities among the thermostability variants.