Substantial Genetic Differentiation in Ayu Plecoglossus altivelis of the Japan and Ryukyu Islands

Abstract

Genetic differentiation in a sample of Ayu (Plecoglossus altivelis) from the Ryukyu Islands and in two samples, an amphidromous population of Kyushu and a landlocked population of Lake Biwa, from the Japan Islands was studied by examining the variation in 28 genetic loci by starch gel electrophoresis. Allele substitutions were observed at virtually 4 loci in the populations of the Japan and Ryukyu Islands. The mean genetic distance between the populations of these two regions was 0.19, which far exceeds the range of distance commonly observed between conspecific populations. Within the Japan Islands, the genetic distance between the amphidromous population of Kyushu and landlocked population of Lake Biwa was much smaller, being 0.02, even though considerable differences in allele frequencies were observed at two loci. These results, along with geological evidence, indicate that Ayu in the Ryukyu Islands has existed as a genetically unique stock isolated from that of the Japan Islands since the middle Pleistocene.