Reproductive costs of anhydrobiosis: female tardigrades protect stored sperm better than males

Anhydrobiosis is a reversible process that allows organisms to survive prolonged periods in a desiccated state. Very little is known about the costs of anhydrobiosis on reproduction beyond a hiatus in activity. Tardigrades are suited to investigate such effects on male gamete function, since the latter can be tracked non-invasively. We compared the effects of three anhydrobiotic state durations (from one day to one month) on male-stored and female-stored sperm function in Macrobiotus dolosus. Our study shows that in-testis sperm motility upon rehydration is considerably impaired after long anhydrobiosis periods, and that its recovery is significantly slowed (up to several days). In contrast, we found no evidence for a negative impact of anhydrobiotic state on the fertilisation ability of spermatheca-stored sperm. Therefore, tardigrade female sperm storage structure can protect stored sperm even during long-term desiccation. Ultimately, our results highlight the need to further study on tissue-specific physiological adaptations to anhydrobiosis.