Trehalose provisioning in Daphnia resting stages reflects local adaptation to the harshness of diapause conditions

Abstract

Environmental fluctuations often select for adaptations such as diapause states, allowing species to outlive harsh conditions. The natural sugar trehalose which provides both cryo- and desiccation-protection, has been found in diapause stages of diverse taxa. Here, we hypothesize that trehalose deposition in resting stages is a locally adapted trait, with higher concentrations produced in harsher habitats. We used resting stages, produced under standardized conditions, by 37 genotypes of Daphnia magna collected from Western Palaearctic habitats varying in their propensity to dry in summer and freeze in winter. Resting eggs produced by D. magna from populations from summer-dry habitats showed significantly higher trehalose than those from summer-wet habitats, suggesting that trehalose has a protective function during desiccation. By contrast, winter-freezing did not explain variation in trehalose content. Adaptations to droughts are important, as summer dryness of water bodies is foreseen to increase with ongoing climate change.

Keywords: Daphnia magna; desiccation; diapause; local adaptation; trehalose.

Figure 1.

Geographical distribution of sampling sites and their habitat types.

Figure 2.

Average trehalose concentration for summer-dry (red) and summer-wet (blue) separated for habitat types (on the left) and for genotypes (on the right). Trehalose concentration is given as a percentage of dry weight per resting egg. Box plots show median, first and third quartile. Whiskers extend to 1.5 times from the interquartile range upper and lower limits. The dots show data points beyond whiskers.