Temperature fluctuations impose significant physiological challenges on aquatic invertebrates, with far reaching consequences that span from cellular to ecosystem levels. Even low to moderate heat stress can activate molecular responses that reshape development, metabolism, and reproduction. In this study, we investigated the transcriptional response of Daphnia pulex, a common grazer in lentic freshwater systems, to sublethal temperature stress (a temperature below the acute lethal limit, allowing for survival during chronic exposure). D. pulex were exposed to control (20℃) and elevated sublethal (25℃) temperatures to simulate an increased water temperature from a mild heat wave for 168 hours. Our findings indicate a dynamic transcriptional response to elevated temperatures. Notably, differential gene expression between the control and temperature-elevated treatment increased throughout the experiment with a three-fold increase in counts of differentially expressed genes (DEGs) from 247 at 96 hours to 743 at 168 hours. Changes in gene expression were related to development, specifically reproduction, at 96 hours, and a shift towards metabolic processes at 168 hours. D. pulex within the experimental treatment generally had higher mean cumulative offspring produced compared to the control treatment. Given D. pulex's role as a foundational species in aquatic food webs, the observed transcriptional response provides insight into the potential for both plastic and adaptive responses in the face of environmental change.
Backenstose et al. (Fri,) studied this question.