2017 Volume 64 Issue 2 Pages 131-138
Genetic disturbance in Japanese wild medaka populations (Oryzias latipes species complex) has resulted mainly from artificial introductions from geographically distinct populations or of commercial varieties, especially an orange-red body color variety (himedaka). Because the extent of genetic introgression within a single water body has remained unclear, the genetic population structure of wild minami-medaka Oryzias latipes in the Nogawa River, a tributary of the Tamagawa River system in Tokyo, Japan, was surveyed using three DNA markers (cytb and ND2 genes on mitochondrial DNA and b-marker on nuclear DNA) to evaluate the extent of introgression throughout upper and lower reaches. Genotypes originating from himedaka were detected at all sites surveyed. Although different genetic composition of introgressed mitotypes among some sampling sites suggested multiple introductions of non-native populations, high dispersal rates of introgressed genes could not be rejected as a cause of wide-spread introgression. Based on this study, appropriate management strategies for the genetic conservation of wild medaka populations are discussed.
