Cyanobacteria-tolerance gene pathways in Daphnia

Cyanobacteria become more prevalent than other phytoplankton in freshwater assemblages, due to global warming and remarkable increases in nutrient fluxes. At such condition, cladocerans, which are dominant zooplankton grazers in freshwater ecosystems, exhibit clonal variation in their tolerance to cyanobacteria with an increasing gradient in eutrophication history. Hitherto, research on the deciphering full modes of action (MoAs) of Daphnia clonal differences in tolerance to toxic Microcystis still remains be in its infancy. In the present study, we conducted fitness and transcriptome analyses on two Daphnia similoides clones (i.e. clone TH09 and TH14). A significant declined body growth rate (BGR; the agent of individual fitness) was detected in the sensitive clone TH09 compared to the tolerant clone TH14 at presence of toxic Microcystis. Furthermore, major MoAs such as glutathione metabolism, protein processing in endoplasmic reticulum, amino sugar/nucleotide sugar metabolism, and arachidonic acid metabolism were linked to the tolerance fitness in D. similoides based on transcriptional analysis. These results extensively provide insights into the pathways of gene and biological processes involved in cyanobacteria tolerance in the Daphnia clonal variation, and propose that understanding the genetic architecture of this fitness-related trait would be helpful to clarify how zooplankton clones adapt to their changing environments.