Biochemical adaptation by the tropical copepods Apocyclops royi and Pseudodiaptomus annandalei to a PUFA-poor brackish water habitat

The cyclopoid Apocyclops royi (Lindberg 1940) and the calanoid Pseudodiaptomus annandalei (Sewell 1919) are 2 tropical copepods suspected of having the capability to biosynthesize the physiologically important n-3 polyunsaturated fatty acids (n-3 PUFAs) eicosapentaenoic acid (C20:5n-3, EPA) and docosahexaenoic acid (C22:6n-3, DHA). We demonstrated this suspected ability using 13C18 α-linolenic acid (C18:3n-3, ALA) fed to the copepods through liposomes and a subsequent fatty acid (FA) analysis by GC-MS at 3 different time points (0, 24, and 48 h). Two different diets were applied post liposome exposure: baker’s yeast Saccharomyces cerevisiae and the microalga Dunaliella tertiolecta. For both copepods, further elongated and desaturated 13C n-3 PUFAs were found at all time points. At T48h, A. royi and P. annandalei contained 13C-labelled DHA contents (±SD) of 1.3 ± 0.2 and 0.7 ± 0.3 µg 13C-FA mgCcopepod-1 when fed baker’s yeast, respectively, and 1.2 ± 0.1 and 1.6 ± 0.5 µg 13C-FA mgCcopepod-1 when fed D. tertiolecta, respectively, with significant differences observed only between P. annandalei diet treatments. The 13C-labelled EPA content of A. royi and P. annandalei at T48h was 0.6 ± 0.4 and 0.7 ± 0.4 µg 13C-FA mgCcopepod-1 when fed baker’s yeast and 0.8 ± 0.2 and 0.3 ± 0.1 µg 13C-FA mgCcopepod-1 when fed D. tertiolecta, with significant differences only between copepods fed D. tertiolecta. A. royi and P. annandalei exhibited an ability to produce n-3 PUFAs from the precursor ALA in comparatively large quantities. This ability enables these 2 species to inhabit habitats characterized by PUFA-poor particulate material.