Demographic processes underlying fitness restoration in bdelloid rotifers emerging from dehydration

Abstract

Bdelloid rotifers are able to survive habitat desiccation in a dehydrated state termed anhydrobiosis. They suffer from decreasing fitness when they are exposed to permanent hydration, yet they restore fitness when they go through anhydrobiosis. The demographic processes underlying this rejuvenation, however, are still largely unknown. \nTo investigate these processes in detail, we analysed life tables of permanently hydrated and repeatedly desiccated lines of two species of bdelloid rotifers, Macrotrachela quadricornifera and Adineta ricciae. Experimental lineages of these two species originated from habitats with contrasting desiccation frequencies. \nFirst, we built a three‐stage life cycle including juveniles as well as prime and senescent adults. Next, we estimated stage‐specific vital rates (survival, development, and reproduction) and used the estimates to project the asymptotic population growth rates λ (= er). Finally, we applied life‐table response experiment methods and performed elasticity analysis to assess the contributions of each vital rate to differences in λ and to estimate effects of proportional changes in vital rates on λ, respectively. \nWe demonstrated that repeatedly desiccated lines grew faster than permanently hydrated lines. In addition, we confirmed that offspring of post‐anhydrobiotic individuals had higher fecundities and matured faster than individuals of the permanently hydrated lines. Survival rates usually did not differ between the two lines, but λ was most elastic to survival rates of prime adults and juveniles. These general life‐history patterns were observed in both species. \nThe analyses performed here provide a detailed investigation of the demographic processes underlying fitness restoration in anhydrobiotic bdelloid rotifers. They reveal that habitat desiccation has profound and consistent effects on the life histories of the two study species. Because laboratory lineages of these species originated from habitats characterised by different wet/dry regimes, we suggest that the desiccation responses identified here may be representative for the entire taxon. As such, our study offers a starting point for comparative analyses beyond bdelloid rotifers.