Insights into the genetic basis of predator-induced response in Daphnia galeata

Phenotypic plastic responses allow organisms to rapidly adjust when facing
environmental challenges - these responses comprise morphological,
behavioral but also life-history changes. Alteration of life-history
traits when exposed to predation risk have been reported often in the
ecological and genomic model organism Daphnia. However, the molecular
basis of this response is not well understood, especially in the context
of fish predation. Here, we characterized the transcriptional profiles of
two Daphnia galeata clonal lines with opposed life histories when exposed
to fish kairomones. First, we conducted a differential gene expression,
identifying a total of 125 candidate transcripts involved in the
predator-induced response, uncovering substantial intra-specific
variation. Second, we applied a gene co-expression network analysis to
find clusters of tightly linked transcripts revealing the functional
relations of transcripts underlying the predator-induced response. Our
results showed that transcripts involved in remodeling of the cuticle,
growth and digestion correlated with the response to environmental change
in D. galeata. Furthermore, we used an orthology-based approach to gain
functional information for transcripts lacking gene ontology (GO)
information, as well as insights into the evolutionary conservation of
transcripts. We could show that our candidate transcripts have orthologs
in other Daphnia species but almost none in other arthropods. The unique
combination of methods allowed us to identify candidate transcripts, their
putative functions and evolutionary history associated with
predator-induced responses in Daphnia. Our study opens up to the question
as to whether the same molecular signature is associated with fish
kairomones-mediated life-history changes in other Daphnia species.