Genetic structure of the endangered red-crowned cranes in Hokkaido, Japan and conservation implications

The red-crowned crane in Japan was once considered extinct due to hunting and habitat destruction in late nineteenth century; however, in 1926, a small group of cranes was rediscovered in the Kushiro Mire in eastern Hokkaido. Since then, various conservation efforts, including artificial feeding during winter, hunting prohibition, and habitat conservation, have increased the population size to > 1400 by 2012. Despite such a successful population recovery, the genetic characteristics of the population have not been fully explored. To ensure the long-term persistence and evolutionary potential of cranes, accurate knowledge of the spatial distribution of genetic variation and its underlying causes are necessary. We assessed their genetic structure using 12 polymorphic microsatellite loci and inferred the mechanisms shaping the observed structure. Among the three regional groups in Hokkaido, we found generally low pairwise F (ST) values and no significant differences in genetic diversity, probably because of the population expansion in the recent past. In contrast, spatial autocorrelation analysis revealed a significant positive kinship at the short distance (0-15 km) and negative kinship at the long distance (155-205 km), showing a pattern of isolation by distance. The presence of isolation by distance on a small spatial scale despite the species' strong flight ability is probably explained by the recolonization process and restricted dispersal due to natal philopatry in a non-equilibrium condition. Cranes in Hokkaido do not appear to be a panmictic (random mating) population; however they can be considered a single population without genetic discontinuity (i.e. a single management unit). Our findings confirm the importance of considering natal philopatry when developing management strategies such as dispersing cranes into unoccupied areas.