Abstract
Calanus copepods are keystone species in marine ecosystems, mainly due to their high lipid content, which is a nutritious food source for e.g. juvenile fish. Accumulated lipids are catabolized to meet energy requirements during dormancy (diapause), which occurs during the last copepodite stage (C5). The current knowledge of lipid degradation pathways during diapause termination is limited. We characterized changes in lipid fullness and generated transcriptional profiles in C5s during termination of diapause and progression towards adulthood. Lipid fullness of C5s declined linearly during developmental progression, but more β-oxidation genes were upregulated in early C5s compared to late C5s and adults. We identified four possible master regulators of energy metabolism, which all were generally upregulated in early C5s, compared to late C5s and adults. We discovered that one of two enzymes in the carnitine shuttle is absent from the calanoid copepod lineage. Based on the geographical location of the sampling site, the field-samples were initially presumed to consist of C. finmarchicus. However, the identification of C. glacialis in some samples underlines the need for performing molecular analyses to reliably identify Calanus species. Our findings contributes to a better understanding of molecular events occurring during diapause and diapause termination in calanoid copepods.
Highlights
Calanus copepods are keystone species in marine ecosystems, mainly due to their high lipid content, which is a nutritious food source for e.g. juvenile fish
During the last copepodite stage (C5), most of the individuals enter into a facultative dormant phase, termed “diapause.” This phase is preceded by accumulation of energy stores as wax esters, which are stored in a specialized organ called the lipid sac
C5s during progression to active adults. This was performed by manually annotating genes in the β-oxidation pathway within the C. finmarchicus transcriptome, and using RNA sequencing to investigate changes in expression of these genes during diapause termination and subsequent molting
Summary
Calanus copepods are keystone species in marine ecosystems, mainly due to their high lipid content, which is a nutritious food source for e.g. juvenile fish. Transcriptomic changes during emergence from diapause have been investigated in the Pacific calanoid copepod Neocalanus flemingeri[18] Beyond these studies, genomic resources for copepods are limited[16,19], and the molecular basis of pathways for lipid degradation and other catabolic processes remains poorly understood in both C. finmarchicus and C. glacialis, in the context of diapause termination. The genes ferritin, heat shock protein 22 (hsp22) and torso-like protein have been linked to developmental progression and/ or diapause in C. finmarchicus[17,30,31] Analyses integrating such biomarkers of energetic metabolism, development and diapause may contribute to elucidating the regulation of lipid metabolism occurring during the termination of diapause in marine copepods
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