Reproduction associated gene expression under predation risk in Daphnia - a comparative transcriptomic approach

Organisms live in a dynamic and often challenging world. Phenotypic plastic responses allow organisms to rapidly adjust to a new environmental situation. Although phenotypic plastic responses to predation risk have been reported for the ecological and genomic model organism Daphnia, their genetic basis is not well understood. Here, we characterized the transcriptional profile of Daphnia galeata when exposed to fish kairomones. First, we investigated the differential gene expression, identifying candidate transcripts being involved in shifts of life history traits in D. galeata. A total of 125 differentially expressed transcripts (40 up- and 85 downregulated) were identified. The expression analysis revealed a surprisingly high variance between clonal lines, likely reflecting their different life history strategies. Second, we applied a gene co-expression network analysis to find clusters of tightly linked transcripts and reveal the genetic pathways underlying predator-induced responses. Our results showed that transcripts involved in remodeling of the cuticle, growth and digestion corresponded to life history shifts in D. galeata. Furthermore, we compared our results with previous studies on other Daphnia species to assess similarities in the predator-induced responses and Daphnia reproduction. Orthologs were identified for D. magna related to predator-induced responses and for D. pulex and D. galeata involved in reproduction. The unique combination of methods including the comparative approach allowed for the identification of candidate transcripts, their functions and orthologs associated with predator-induced responses and reproduction in Daphnia.