The β-oxidation pathway is downregulated during diapause termination in Calanus copepods

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.

Lipid metabolism in Calanus finmarchicus is sensitive to variations in predation risk and food availability

“…Our observations of general ß-oxidation gene expression pattern across treatments, relative to the reference group, further supports a higher lipid catabolism rate in C4s and early C5s, and a decline in late C5s and C6s. In a recent study by , where Calanus C5s terminated diapause without available food, lipid catabolism was also higher early in the C5 stage and declined close to the terminal molt to C6 21 . Thus, a similar pattern in lipid catabolism seems to occur in the late life stages in Calanus copepods, perhaps regardless of activity level, but modulated by both food availability and predation risk.…”

“…6a) and ferritin ( Fig. 6b), two molecular markers showing high expression during diapause in C. finmarchicus 20,21,39 , was significantly (P < 0.01, details in Supplementary Table 2) downregulated in C4, C5 and C6 copepodites in all treatment groups on all days compared to the reference group. Ferritin was significantly upregulated in late C5s with low food and no predator compared to those with low food and a predator cue (logFC = 0.49, P = 0.049, FDR = 1), and in C6s with high food and no predator cue compared to C6s with a predator cue and high food (logFC = 0.680, P < 0.01, FDR = 0.57) and low food (logFC = 0.56, P = 0.03, FDR = 0.64, all results from statistical tests are available in Supplementary Table 2).…”

“…The reference group, consisting of Calanus spp. copepodites of stage C5, was collected from sea bed depth (400 m) up to 200 m in the Trondheimsfjord, Norway (N63° 29′, E10° 18) in August 2017 using methods described in Skottene et al 21 . The copepod samples (n = 3, 10 individuals per tube) were placed in microcentrifuge tubes with 1.5 mL of RNAlater (Ther-moFisher, USA) as soon as possible after collection, while onboard the research vessel.…”

“…Regardless of external cues, the ability to accumulate sufficient lipids to survive months without feeding is an important aspect of diapause preparation [17][18][19][20][21][22] . The Lipid Accumulation Window (LAW) hypothesis postulates that individual copepods must achieve a certain level of stored lipids in order to initiate diapause [22][23][24][25] .…”

Gene expression in diapausing rotifer eggs in response to divergent environmental predictability regimes

“…www.nature.com/scientificreports/ utilized as an energy source by the end of diapause when neutral lipid storage becomes depleted 65,66 . It is known that the diapausing eggs of rotifers store fat reserves 42 and it is likely that harvesting of lipids for the embryo starts at the time of diapausing egg production (diapause initiation); however, no molecular function associated with lipid metabolism had annotated DEGs that related to the predictability regime in our study.…”