Fatty acid bioconversion in harpacticoid copepods in a changing environment: a transcriptomic approach

Abstract

By 2100, global warming is predicted to significantly reduce the capacity of marine primary producers for long-chain polyunsaturated fatty acid (LC-PUFA) synthesis. Primary consumers such as harpacticoid copepods (Crustacea) might mitigate the resulting adverse effects on the food web by increased LC-PUFA bioconversion. Here, we present a high-quality de novo transcriptome assembly of the copepod Platychelipus littoralis , exposed to changes in both temperature (+3°C) and dietary LC-PUFA availability. Using this transcriptome, we detected multiple transcripts putatively coding for LC-PUFA-bioconverting front-end fatty acid (FA) desaturases and elongases, and performed phylogenetic analyses to identify their relationship with sequences of other (crustacean) taxa. While temperature affected the absolute FA concentrations in copepods, LC-PUFA levels remained unaltered even when copepods were fed an LC-PUFA-deficient diet. While this suggests plasticity of LC-PUFA bioconversion within P. littoralis , none of the putative front-end desaturase or elongase transcripts was differentially expressed under the applied treatments. Nevertheless, the transcriptome presented here provides a sound basis for future ecophysiological research on harpacticoid copepods. 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'.

A complete enzymatic capacity for biosynthesis of docosahexaenoic acid (DHA, 22 : 6n–3) exists in the marine Harpacticoida copepod Tigriopus californicus

“…Copepods, one of the most abundant groups within zooplankton, contain high levels of n-3 LC-PUFA, particularly EPA and DHA [21,55], prompting interest to elucidate to which extent biosynthesis, along diet can contribute to the abundance of these essential nutrients. While several studies provided evidence suggesting that some copepod species can indeed produce LC-PUFA endogenously, the potential contribution of microbial endosymbionts for such metabolic ability could not be completely ruled out [31][32][33]. In the present study, we addressed this methodological drawback by performing a comprehensive retrieval for all genes encoding desaturase and elongase enzymes with potential roles in the PUFA and LC-PUFA biosynthesis in a representative species within Harpacticoida, T. californicus.…”

“…Early studies using 14 C-labelled fatty acids suggested some copepods showed the ability to bioconvert PUFA into LC-PUFA [23,24]. Studies involving feeding trials using LC-PUFA-deficient diets or stable isotope labelled fatty acids provided further evidence that Harpacticoida and Cyclopoida copepods possess some capacity to produce n-3 LC-PUFA endogenously [25][26][27][28][29][30][31][32][33]. However, these studies could not unequivocally establish that the abovementioned metabolic activities observed were indeed due to the copepod's enzymatic complement, and hence it is difficult to completely rule out that LC-PUFA are rather synthesized by microbes that coexist within the copepod.…”

“…In addition, it is unclear whether, beyond ωx desaturases, copepods have further enzymes such as front-end desaturases and fatty acyl elongases that, along ωx desaturases, enable complete enzymatic activities allowing the production of a variety of LC-PUFA including DHA (figure 1). Recent studies involving genomic and transcriptomic analyses identified sequences of desaturase and elongase genes with putative roles in the LC-PUFA biosynthesis in Harpacticoida and Cyclopoida copepods [31][32][33][34]. However, no functional evidence demonstrating the actual role of these enzymes in the LC-PUFA biosynthetic pathways was reported.…”

First De Novo Transcriptome of the Copepod Rhincalanus gigas from Antarctic Waters

“…The number of high-quality transcriptomes, especially for copepods, is still limited, although, in recent years, there has been an increase in molecular resources for metazoan zooplankton [ 31 , 32 , 33 , 34 , 35 , 36 , 37 ]. In this study, we present the first molecular resource for an eucalanoid copepod, Rhincalanus gigas .…”

The critical importance of experimentation in biomarker-based trophic ecology

“…With primary consumers, it is relatively easy to provide fresh, single species of phytoplankton or macroalgae as foods that are likely representative of nature since many short-lived primary consumers feed on temporally limited algal blooms. In this special issue, numerous authors employed this approach and focused on feeding pure algal diets [20,21,29,30,33,34]; with their springtail experiments Kühn et al [35, this issue] were also able to offer mixed dried diets of bacteria, microalgae, fungi and plants. At intermediate trophic levels, it can be difficult to meet the nutritional requirements of consumers by feeding single species, particularly for longer-duration experiments, since such predators are rarely so specialized [28,31].…”