Establishment of a Rearing System of the Extremotolerant Tardigrade Ramazzottius varieornatus: A New Model Animal for Astrobiology

Abstract

Studies on the ability of multicellular organisms to tolerate specific environmental extremes are relatively rare compared to those of unicellular microorganisms in extreme environments. Tardigrades are extremotolerant animals that can enter an ametabolic dry state called anhydrobiosis and have high tolerance to a variety of extreme environmental conditions, particularly while in anhydrobiosis. Although tardigrades have been expected to be a potential model animal for astrobiological studies due to their excellent anhydrobiotic and extremotolerant abilities, few studies of tolerance with cultured tardigrades have been reported, possibly due to the absence of a model species that can be easily maintained under rearing conditions. We report the successful rearing of the herbivorous tardigrade, Ramazzottius varieornatus, by supplying the green alga Chlorella vulgaris as food. The life span was 35 +/- 16.4 d, deposited eggs required 5.7 +/- 1.1 d to hatch, and animals began to deposit eggs 9 d after hatching. The reared individuals of this species had an anhydrobiotic capacity throughout their life cycle in egg, juvenile, and adult stages. Furthermore, the reared adults in an anhydrobiotic state were tolerant of temperatures of 90 degrees C and -196 degrees C, and exposure to 99.8% acetonitrile or irradiation with 4000 Gy (4)He ions. Based on their life history traits and tolerance to extreme stresses, R. varieornatus may be a suitable model for astrobiological studies of multicellular organisms.

Effect of lifespan and age on reproductive performance of the tardigrade Acutuncus antarcticus: minimal reproductive senescence

“…Lifespan of A. antarcticus varied greatly among the individuals examined, as has been noted in studies of other tardigrade species (Suzuki, 2003;Horikawa et al, 2008;Schill, 2013;Altiero et al, 2015). Considerable variation in lifespan between individuals within isogenic populations under constant laboratory conditions has also been observed in a model animal of ageing studies, the nematode Caenorhabditis elegans (Kirkwood & Finch, 2002), and also in the monogonont rotifers Asplanchna brightwelli and Brachionus manjavacas (Snell & King, 1977;Snell et al, 2012).…”

The Tardigrade Ramazzottius varieornatus as a Model Animal for Astrobiological Studies

“…Under the culture conditions described, the average life span of R. varieornatus was approximately 35 d, and the maximum life span was 87 d (Horikawa et al, 2008). The average number of eggs produced by a single individual was 7.85, and the first egg laying was observed 9 d after hatching (Horikawa et al, 2008).…”

“…varieornatus, originally collected from the dry moss vegetation on a bridge in Sapporo, Japan, was cultured with the green alga C. vulgaris (Chlorella Industry Co., Ltd., Tokyo, Japan) as food (Horikawa et al, 2008) (Fig. 1A, B; Fig.2 A).…”

“…The average number of eggs produced by a single individual was 7.85, and the first egg laying was observed 9 d after hatching (Horikawa et al, 2008). Of the eggs produced, 83% hatched, and the average embryonic stage was 5.7 d (Horikawa et al, 2008).…”

“…To further develop tardigrades as a model for astrobiological studies, we recently established culture systems for the tardigrade species Ramazzottius varieornatus using a green alga, Chlorella vulgaris, as food (Horikawa et al, 2008). Our findings indicate that this species has high anhydrobiotic ability and is tolerant to several types of extreme environmental conditions (Horikawa et al, 2008). Here, I review the culture systems, life history, anhydrobiosis, and environmental tolerance of R. varieornatus and propose that this species, particularly among tardigrades, is a suitable model animal for astrobiological studies.…”