Interspecific variation in cyanobacteria–temperature interaction on life history and gut microbiota of water fleas

Context: Cyanobacterial blooms are seasonal, yet past studies on their impact on zooplankton have mostly overlooked temperature changes. Aims: To investigate the interactive effects of cyanobacteria and temperature on the life-history traits and gut microbiota composition of distinct cladoceran species. Methods: Under four temperature conditions, the detrimental impacts of cyanobacteria on two cladoceran species (Daphnia pulex and Simocephalus vetulus) were investigated. The life-history traits were documented through life-table experiments. The gut microbiota composition was determined by terminal-restriction fragment-length polymorphism and 16S rRNA gene sequencing. Key results: D. pulex exhibited the worst performance when exposed to both high temperature and cyanobacteria, whereas S. vetulus could still maintain favorable conditions. These stressors significantly altered the gut microbiota composition of D. pulex, whereas that of S. vetulus remained reasonably stable under different temperature and food treatments and contained two bacterial genera potentially contributing to cyanobacterial tolerance. Conclusions: Compared with S. vetulus, D. pulex exhibited greater susceptibility to the combined effects of cyanobacteria and temperature. The changes of dominant symbiotic bacteria might indicate the adverse state of water fleas under stress. Implications: Our research demonstrated that warming combined with cyanobacterial blooms poses a greater threat to D. pulex than to S. vetulus.