Abstract
Late developmental stages of the marine copepods in the genus Calanus can spend extended periods in a dormant stage (diapause) that is preceded by the accumulation of large lipid stores. We assessed how lipid metabolism during development from the C4 stage to adult is altered in response to predation risk and varying food availability, to ultimately understand more of the metabolic processes during development in Calanus copepods. We used RNA sequencing to assess if perceived predation risk in combination with varied food availability affects expression of genes associated with lipid metabolism and diapause preparation in C. finmarchicus. The lipid metabolism response to predation risk differed depending on food availability, time and life stage. Predation risk caused upregulation of lipid catabolism with high food, and downregulation with low food. Under low food conditions, predation risk disrupted lipid accumulation. The copepods showed no clear signs of diapause preparation, supporting earlier observations of the importance of multiple environmental cues in inducing diapause in C. finmarchicus. This study demonstrates that lipid metabolism is a sensitive endpoint for the interacting environmental effects of predation pressure and food availability. As diapause may be controlled by lipid accumulation, our findings may contribute towards understanding processes that can ultimately influence diapause timing.
Highlights
Influence a range of life history traits in marine copepods, including growth, development and reproduction[12,13,14], but the role of predation risk in shaping zooplankton life history has been much less explored in the ocean than in freshwater and estuarine e nvironments[15,16]
In order to assess this aim, we investigated the effects of perceived predation risk and varying food availability on molecular indicators of lipid metabolism in C. finmarchicus copepodites during the transitions from the C4 to the C6 stage (Fig. 1 shows treatment combinations and timeline of the experiment)
We have demonstrated that predator cues and food availability interactively influence lipid metabolism in C. finmarchicus copepodites developing from the C4 copepodite stage via C5 to the adult female stage
Summary
In C4s, there was no clear effect of the treatments on the expression of ß-oxidation genes, except for a pattern of upregulation in the C4s with high food and a predator cue relative to those with low food and a predator cue (Fig. 4, details presented in Supplementary Table 5). The reaction product is fatty acyl-CoA, and it is catalyzed by a long-chain fatty acid CoA ligase (EC number 6.2.1.3, “FA ligase” hereafter), for which several transcripts have been identified in the C. finmarchicus transcriptome[21] In both early and late C5s, there was a pattern of downregulation of ß-oxidation genes with high food availability relative to low food, both with and without a predator cue Number of significant (P < 0.05) differentially expressed ß-oxidation genes (x-axis) between experimental treatments (y-axis, left) in Calanus finmarchicus copepods exposed to a combination of presence or absence of a predator cue with high or low food availability. It was recently reported that both C. finmarchicus and C. glacialis occur in the Trondheimsfjord[3], from where the NTNU Sealab culture was originally collected (in 2004)
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