Life history traits for the freshwater Tardigrade Species Hypsibius exemplaris reared under laboratory conditions

Known tardigrade species have increased in number over the years, but individual life history traits for most are unknown. The present study documents life history traits such as growth, reproductive activity, and lifespan for the parthenogenetic Eutardigrada species Hypsibius exemplaris when reared under laboratory conditions. Embryos were characterized by 100% hatching success, and hatchlings were characterized by approximately 90% survival to sexual maturity and 80% healthy growth to adult size, suggesting that mortality and growth defects occur early in life history. Egg production increased with age, eggs per exuvium maximizing on days 18, 21, and 24 post-hatching. The mean lifespan was 61.9 ± 9.9 days, with the maximum, 75 days, achieved by four among the 70 individuals whose life histories were documented. Given its short generation time, amenability to laboratory conditions, stereotypical embryonic stages, recently sequenced genome, and now chronicled life history, H. exemplaris rapidly is becoming a popular candidate in the phylum Tardigrada for advancing scientific inquiry.