The intertidal harpacticoid copepod Platychelipus littoralis (Brady, 1880) has the ability to bioconvert short-chain fatty acids deriving from their diet and produce essential polyunsaturated fatty acids (PUFA). This ability was investigated in a short-term experiment where P. littoralis was fed on PUFA-rich Nitzschia sp. and PUFA-poor D. tertiolecta, and was exposed to current pH (8 ± 0.2 units) and predicted pH conditions by the end of the century (7.5 ± 0.2 units). Furthermore, fatty acid profiles and relative expression of genes encoding putative fatty acid desaturases (FAD) and elongases (elovl) were analyzed. The copepods exhibited similar composition of fatty acids despite of the diet and pH, showing that efficiently bioconverted PUFA. Transcripts coding some enzymes (FAD Δ4, Δ5, Δ9 and elovl2) involved in the PUFA biosynthesis pathway were retrieved from the transcriptome of P. littoralis. Relative gene expression analysis revealed not only a significant relative upregulation of FAD Δ5, Δ9 and elovl2 when fed on PUFA-poor, but also a significant relative upregulation of FAD Δ5 and Δ9 when exposed to acidic pH. These results suggest that low-quality food induces bioconversion to compensate the lack of PUFA.
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