Spatio-temporal patterns in the gene expression of the calanoid copepod Temora longicornis in the Belgian part of the North Sea.

Marine zooplankton are increasingly being affected by recent environmental changes, such as climate change, and respond with profound spatial relocations and shifts in phenology and physiology. In order to predict whether populations are able to persist or adapt to such new conditions, it is essential to understand the molecular basis of such adaptations, which ultimately get translated into these physiological responses. To explore variation in population gene expression across time and space, we investigated transcriptome-level profiles of the calanoid copepod Temora longicornis, that were collected at four different locations in the Belgian Part of the North Sea (BPNS) on three different time points (April, June, October) in 2018. RNA-seq analysis of field collected adults identified large seasonal differences in gene expression, mainly between spring-summer and autumn samples. The largest log-fold changes occurred in a set of genes encoding for ribosomal and myosin (heavy chain) transcripts. Enrichment analysis revealed a strong seasonal pattern in vitellogenin, cuticle and glycolytic gene expression as well. We also found a positive correlation between vitellogenin expression and densities of T. longicornis. No clear spatial variation in expression patterns was found in the BPNS. This study underlines the potential of field gene expression studies for biomonitoring purposes and the significance of considering seasonal variation in future studies.