Slow desiccation improves dehydration tolerance and accumulation of compatible osmolytes in earthworm cocoons (Dendrobaena octaedraSavigny)

Abstract

SUMMARYThe earthworm, Dendrobaena octaedra, is a common species in temperate and subarctic regions of the northern hemisphere. The egg capsules (ʻcocoonsʼ) of D. octaedra are deposited in the upper soil layers where they may be exposed to desiccation. Many previous studies on desiccation tolerance in soil invertebrates have examined acute exposure to harsh desiccating conditions, however, these animals are often more likely to be exposed to a gradually increasing drought stress. In the present study we slowly desiccated D. octaedra cocoons to simulate ecologically realistic drought conditions and the results clearly demonstrate that gradually dehydrated cocoons show an increased tolerance of extreme drought compared with acutely dehydrated cocoons. NMR spectroscopic analysis of compatible osmolytes revealed the presence of sorbitol, glucose, betaine, alanine and mannitol in dehydrated embryos. The superior drought survival of gradually desiccated embryos could partly be attributed to a higher accumulation of osmolytes (especially sorbitol). Thus, gradually and acutely desiccated embryos accumulated ~2·mol·l -1 and 1·mol·l -1 total osmolytes, respectively. However, in addition to osmolyte accumulation, the gradually desiccated cocoons also tolerated a higher degree of water loss, demonstrating that gradually dehydrated D. octaedra cocoons are able to survive loss of ~95% of the original water content. Although D. octaedra embryos can probably not be categorized as a truly anhydrobiotic organism we propose that they belong in a transition zone between the desiccation sensitive and the truly anhydrobiotic organisms. Clearly, these earthworm embryos share many physiological traits with anhydrobiotic organisms.

The genome and phenome of the green alga Chloroidium sp. UTEX 3007 reveal adaptive traits for desert acclimatization

“…UTEX 3007 have been shown to promote desiccation tolerance in a wide variety of species (Bradbury, 2001; Breeuwer et al, 2003; Petersen et al, 2008; Petitjean et al, 2015; Santacruz-Calvo et al, 2013; Watanabe et al, 2016). Uncommon sugars are known to be involved in the stress responses of green algae, but their constituents vary widely between even closely related species (Gustavs et al, 2010).…”

Sharing the burden? Earthworms and woodlice show seasonal complementarity in peak abundances in soil in an oak-beech temperate woodland

“…Soil moisture content is highest during the winter months when earthworms are at their most abundant and this because earthworms are extremely sensitive to desiccation. During drought conditions earthworms either aestivate (Edwards and Bohlen, 1996) or survive as cocoons (Petersen et al, 2008). Few adults can survive low soil moisture conditions, so when soil moisture is lowest during the summer months, earthworm abundance and activity is lowest.…”

The Cocoon of the Fossorial FrogCyclorana australisFunctions Primarily as a Barrier to Water Exchange with the Substrate

“…The accumulation of epithelial layers is similar in all cocooning anurans; hence, we anticipate that the findings for C. australis are applicable to other species. Cocoon formation has been documented in other burrowing organisms (Greenwood 1986;Pusey 1986;Etheridge 1990;Petersen et al 2008), and although some cocoons are comprised solely of mucus, others are formed from multiple epithelial layers. Most, if not all, cocooning species live in arid or seasonally dry environments where water becomes unavaüable (either for drinking or via osmotic uptake).…”