 Its closest living relation is "Octomys mimax", the Andean Viscacha-Rat of the same family, whose 2"n" = 56.It was therefore surmised that an "Octomys"-like ancestor produced tetraploid (i.e., 2"n" = 4"x" = 112) offspring that were, by virtue of their doubled chromosomes, reproductively isolated from their parents.Polyploidy was induced in fish by Har Swarup (1956) using a cold-shock treatment of the eggs close to the time of fertilization, which produced triploid embryos that successfully matured.