Tokudaia is a genus of murinerodent native to Japan.[1] Known as Ryūkyū spiny rats or spinous country-rats, population groups exist on several non-contiguous islands.[2] Despite differences in name and appearance, they are the closest living relatives of the Eurasian field mouse (Apodemus). Of the three species, both T. osimensis and T. tokunoshimensis have lost their Y chromosome and SRY gene; the sex chromosomes of T. muenninki, on the other hand, are abnormally large.[3]
^Sutou, S.; Mitsui, Y.; Tsuchiya, K. (2001). "Sex determination without the Y Chromosome in two Japanese rodents Tokudaia osimensis osimensis and Tokudaia osimensis spp". Mammalian Genome. 12 (1): 17–21. doi:10.1007/s003350010228.