Assimilation and turnover rates of lipid compounds in dominant Antarctic copepods fed with 13 C-enriched diatoms

Martin Graeve,Lauris Boissonnot,Barbara Niehoff,Gerhard Kattner,Wilhelm Hagen

doi:10.1098/rstb.2019.0647

Abstract

The study revealed species- and stage-specific differences in lipid accumulation of the dominant Antarctic copepods, the primarily herbivorous Calanoides acutus (copepodite stage V (CV), females) and the more omnivorous Calanus propinquus (females) storing wax esters and triacylglycerols, respectively, which were collected in summer (end of December). Feeding carbon-labelled diatoms to these copepods, 13C elucidated assimilation and turnover rates of copepod total lipids as well as specific fatty acids and alcohols. The 13C incorporation was monitored by compound-specific stable isotope analysis (CSIA). CV stages of C. acutus exhibited an intense total lipid turnover and 55% of total lipids were labelled after 9 days of feeding. By contrast, total lipid assimilation of female C. acutus and C. propinquus was lower with 29% and 32%, respectively. The major dietary fatty acids 16:0, 16:1(n − 7) and 20:5(n − 3) had high turnover rates in all specimens. In C. acutus CV, the high rates of the de novo synthesized long-chain monounsaturated fatty acids and alcohols 20:1(n − 9) and 22:1(n − 11) indicate intense lipid deposition, whereas these rates were low in females. The differences in lipid assimilation and turnover clearly show that the copepod species exhibit a high variability and plasticity to adapt their lipid production to their various life phases.This article is part of the theme issue ‘The next horizons for lipids as ‘trophic biomarkers': evidence and significance of consumer modification of dietary fatty acids'.

Highlights

IntroductionPrimary production varies considerably throughout the year, especially in boreal, polar and upwelling regions
In marine ecosystems, primary production varies considerably throughout the year, especially in boreal, polar and upwelling regions
We examined the hypothesis that wax esters can be more rapidly biosynthesized than triacylglycerols, since the reduction of fatty acids to alcohols diminishes a negative feedback mechanism, which occurs in the presence of surplus fatty acids [2]

Summary

Introduction

Primary production varies considerably throughout the year, especially in boreal, polar and upwelling regions. To cope with unfavourable conditions, i.e. periods of low food supply, herbivorous zooplankton, in particular calanoid copepods, have developed specific biochemical strategies [1,2,3] They massively accumulate and store neutral lipids during the productive season, usually in the form of wax esters or triacylglycerols. The huge lipid deposits accumulated by herbivorous zooplankton species, in particular calanoid copepods, are partly biosynthesized de novo from the phytoplankton diet, but they contain specific phytoplankton fatty acids incorporated without biochemical alteration. Boissonnot et al used the same labelling technique on small Arctic copepods [18] They showed that the herbivorous Pseudocalanus minutus exhibited high lipid turnover rates and that the species incorporated fatty acids more rapidly from diatoms than from flagellates. One-way ANOVA followed by Tukey honest significant difference tests were performed on the slope of linear regressions

Results

Findings

Discussion

Summary and conclusion