Reproductive performance of the Antarctic tardigrades, Acutuncus antarcticus (Eutardigrada: Hypsibiidae), revived after being frozen for over 30 years and of their offspring

Studies on the long-term survival of animals often focus on the specific instance of survival of animals only, and descriptions of subsequent reproduction are generally not reported. In this study, we recorded the reproductive performance of the first-generation offspring of the resuscitated individual (SB-1) and the hatchling of the resuscitated egg (SB-3) of the Antarctic tardigrade, Acutuncus antarcticus, after being frozen for 30.5 years. By providing further detailed description of the reproduction of SB-1 and SB-3 after revival, and then comparing the reproductive performance with that of their first-generation offspring, the possible indications of the damage accrued during the long-term preservation in SB-1 and SB-3 were more specifically detected. Additionally, the DNA analysis revealed two distinctively different mitochondrial genetic sequences of A. antarcticus between the SB strains and the LSW strain. The observed differences in some of the reproductive parameters between the two genetic types suggested a possible relationship between the life-history traits and genetic type in the species A. antarcticus. Further experiments using the SB-1 and SB-3 strains reared for a long period to exclude the instant effect of preservation are expected to improve our understanding of the mechanisms underlying the long-term survival of animals.