Lipid metabolism and diapause timing in Calanus copepods: The impact of predation risk, food availability and oil exposure
Doctoral thesis
Permanent lenke
https://hdl.handle.net/11250/2980904Utgivelsesdato
2021Metadata
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- Institutt for biologi [2512]
Sammendrag
Calanoid copepods of the Calanus genus have an important ecological role as energetic links between primary producers and higher trophic level species in the North Atlantic and Arctic Oceans. Most individuals spend a large part of the year in deep waters in a dormant state called diapause, and they resurface to feed and reproduce in timing with the spring phytoplankton bloom. The metabolism of stored lipid is hypothesized to have a key role in the timing of diapause, but details regarding metabolic processes during diapause are scarce. The overarching aim of this thesis was to understand more of the metabolic patterns in Calanus copepods that develop through the last copepodite stages, focusing on the accumulation and utilization of stored lipid in the context of diapause timing. If drastic changes in the environment disrupt copepod lipid metabolism, diapause timing could be altered. Climate change can alter both predation risk and food availability for Calanus copepods, and oil production in the North Atlantic and Arctic regions involves an inherent risk of oil exposure to Calanus copepods that will remain relevant during the next decades. Therefore, the sensitivity of lipid metabolism in Calanus copepods during the life stages preceding and including diapause, to varying food availability and predation risk, and to oil component exposure was assessed.
Several aspects of lipid metabolism were investigated in copepods in different conditions during development: i) during direct development from copepodite stage C4 via C5 to the final adult stage (C6) under four treatment combinations with varying predation risk and food availability, ii) during development from C5s in diapause through diapause termination and molting to C6, and iii) during development from C5s in diapause through diapause termination and molting to C6, including an exposure period (five days) to petrogenic oil components in a water soluble fraction (WSF) of crude oil. Both targeted and untargeted gene expression analyses were used to assess variation in metabolic processes, as well as lipid fullness assessments.
i) In active copepods (Paper I), lipid accumulation increased through the C4 and C5 stages, and declined in C6. Lipid accumulation became reduced in groups with predation cues, particularly with low food availability. Lipid catabolism generally declined with development across the treatments and became reduced in C5s with predation cues in both high and low food availability. ii) In unfed Calanus C5s terminating diapause (Paper II), lipid catabolism generally declined with development as the lipid content declined. In this study, potential master regulators of lipid metabolism were identified, and assisted in generating an hypothesized trend of lipid catabolic rates during diapause in Calanus copepods. In brief, lipid catabolism declines towards diapause termination, and appears to be higher at an early point during diapause, rather than in direct association with molting to C6. iii) In Calanus copepods terminating diapause, WSF-exposure resulted in reduced lipid catabolism (Paper III). The WSF-exposed copepods had a slower reduction in lipid content over time than the control copepods, an observation which was supported by the expression patterns of ß-oxidation genes.
Potential explanations for and implications of the lipid metabolic responses to variations in food availability and predation risk, and to oil exposure are explored in this thesis. The sensitivity of copepod lipid metabolism to these factors can have implications for the copepods’ ability to achieve the lipid requirements for diapause induction and termination. Our results imply that drastic changes in these environmental and anthropogenic factors could affect the timing of diapause, which has the potential to alter marine ecosystem dynamics.