Transcriptome-wide genotype-phenotype associations in Daphnia in a predation risk environment.

Phenotypic variation plays an important role in how species cope with environmental challenges. Pinpointing which genes and genomic regions are underlying phenotypic variability thus helps to understand the processes of acclimation and adaptation. We used Daphnia as a system to identify candidates playing a role in phenotypic variation related to a predation risk environment with a genome-wide association approach. Furthermore, a gene co-expression network analysis allowed identifying clusters of co-expressed genes which correlated to life history traits. To enhance the understanding of the functional roles of the transcripts, we identified orthologs and paralogs from related species and used ontologies to annotate the candidates of interest. Our study revealed that only one life history trait and two morphometric traits have a genetic association in the presence of predation risk (fish kairomones), whereas most genotype-phenotype associations were detected in a genotype-environment interaction analysis for reproduction-related phenotypic traits. The gene co-expression network analysis identified a total of 44 modules, of which one module correlated to another life history trait namely the 'total number of broods'. The combined use of gene co-expression network and transcriptome-wide association analysis allowed the identification of 131 candidate transcripts associated with life history traits in Daphnia galeata. These results lay the ground for targeted studies to further understand phenotypic variability in this species.