瀬戸内海東部海域のメイタガレイ同胞種の遺伝生化学的検出と形態学的検討

Abstract

The occurrence of a sibling species of the frog flounder Pleuronichthys cornutus was uncovered by population analysis of allelic variations at three enzyme loci for 272 specimens of 8 population samples collected from the eastern part of the Seto Inland Sea. The sibling species (type B) was discovered in a population sample (WK) collected at the Kiisuido Channel, and highly resembled P. cornutus (type A) in morphological features, which is commonly distributed in this area. Type B, however, could clearly be distinguished by genotypes at Mdh-B and Icd-B loci, respectively, coding for malate dehydrogenase-B and isocitrate dehydrogenase-B. All the specimens of type B showed genotype B2B2 at Mdh-B locus and B3B3 at Ied-B locus. In the population sample WK, a remarkable homozygote excess was observed at these two loci, all the remaining specimens except the genotypes mentioned above were type A which had genotypes B1B1 at Mdh-B locus and B1B1 at Icd-B locus, and no heterozygotes were found at these loci. At another locus coding for α-glycerophosphate dehydrogenase, the same homozygote excess was demonstrated, and different alleles were predominant in types A and B. Morphological examination of the two types revealed that the number of dorsal, anal and ventral fin rays was fewer in type B than in type A, and the differences were statistically significant in most cases, but differences as to several other meristic characters and relative growth of body parts to body length were not significant. Differences in spots and coloration on the body surface and the possibility of isolation by a difference in spawning season between the two types are dis-cussed.