Genetic differentiation between introduced Central European sika and source populations in Japan: effects of isolation and demographic events

Japanese sika deer (Cervus nippon nippon) were introduced at the turn of nineteenth and twentieth century to many countries in Eurasia, North America and Australasia. Subsequently, free-living invasive populations have become established in several countries, including the Czech Republic, where the expanding sika population causes serious problems through overgrazing, damage through browsing and through competition and hybridisation with native red deer. 122 Japanese and 221 Czech samples were used to examine the genetic diversity, genetic structure, and the level of genetic differentiation between native populations and those introduced to the Czech Republic. Analyses of 22 microsatellite loci revealed, for both countries, evidence of isolation by distance and clear sub-structuring of populations, different from patterns previously revealed by mtDNA markers. The high number of private alleles (58 within the Czech Republic and 84 within Japan), the Fst values, factorial correspondence analysis and Bayesian clustering support a high level of divergence between the source and introduced populations. Genetic variability was generally low due to recent demographic events (founder effect in the Czech population, bottlenecks in Japanese populations); however, the values of expected heterozygosity differed greatly between subpopulations and were not the lowest in the introduced Czech populations. Multiple introductions, rapid population growth, and possible hybridisation with red deer seem to have helped the successful expansion of sika within the Czech Republic. The results also indicate that male-mediated gene flow and human-mediated translocations have significantly influenced the current genetic structure of native sika populations in Japan.