We conducted genetic assessment on a postulated hybrid population between Taiwan macaques (Macaca cyclopis) and Japanese macaques (M. fuscata) inhabiting Ooike and the surrounding area in Wakayama prefecture in 1999. The population originated with the introduction of Taiwan macaques in the area in 1955. Two social groups, of approximately 200 animals in total were observed, indicating an annual growth rate of 3.0-6.7% following introduction. From our analysis of diagnostic genetic markers (three kinds of blood proteins and mitochondrial DNA D-loop sequence), the degree of interspecific hybridization could be quantified and the breeding structure assessed. Six of the nine animals examined were identified as hybrids born in the study area after more than one generation of mixture. Two of the remaining animals showed a Taiwanese macaque-like genetic profile and the last was Japanese macaque-like. Approximately one forth of the Taiwanese gene pool has already been replaced with Japanese macaque genes over the last 45 years. The migration rate from out groups of native Japanese macaques was estimated to be 0.6% per year and 5.9% per generation. These results strongly suggest that the two macaque species are intermixing without reproductive constraint in the area. This man made hybrid zone risks disturbing of the gene pools and biological features of native Japanese macaques in surrounding areas. The impact of expansion of exotic genes into Japanese macaque habitats is discussed based on the obtained estimates of demographic and genetic parameters.
