Inter- and intraspecific differences in rotifer fatty acid composition during acclimation to low-quality food

Abstract

Biochemical food quality constraints affect the performance of consumers and mediate trait variation among and within consumer species. To assess inter- and intraspecific differences in fatty acid retention and conversion in freshwater rotifers, we provided four strains of two closely related rotifer species, Brachionus calyciflorus sensu stricto and Brachionus fernandoi, with food algae differing in their fatty acid composition. The rotifers grazed for 5 days on either Nannochloropsis limnetica or Monoraphidium minutum, two food algae with distinct polyunsaturated fatty acid (PUFA) profiles, before the diets were switched to PUFA-free Synechococcus elongatus, which was provided for three more days. We found between- and within-species differences in rotifer fatty acid compositions on the respective food sources and, in particular, highly specific acclimation reactions to the PUFA-free diet. The different reactions indicate inter- but also intraspecific differences in physiological traits, such as PUFA retention, allocation and bioconversion capacities, within the genus Brachionus that are most likely accompanied by differences in their nutritional demands. Our data suggest that biochemical food quality constraints act differently on traits of closely related species and of strains of a particular species and thus might be involved in shaping ecological interactions and evolutionary processes. 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'.

Keywords: Brachionus; PUFA composition; fatty acids; food quality; rotifer strains; trait variation.

Figure 1.

Fatty acid concentrations (a) and proportions of saturated, monounsaturated and polyunsaturated fatty acids (SFA, MUFA and PUFA, respectively) (b) of Monoraphidium minutum, Nannochloropsis limnetica and Synechococcus elongatus used as food algae in the rotifer experiments. Data represent means ± s.d., number of replicates N = 3.

Figure 2.

(a,b) Principal component analysis (PCA) of fatty acid profiles of three strains of Brachionus calyciflorus s.s. (open symbols) and one strain of Brachionus fernandoi (filled symbols) fed Monoraphidium minutum (Mon; light green symbols) and Nannochloropsis limnetica (Nan; yellow symbols) either continuously or initially prior to a food switch to Synechococcus elongatus. Rotifers fed S. elongatus are separated depending on whether they fed either M. minutum (MonSyn; dark green symbols) or N. limnetica (NanSyn; red symbols) before the food source was switched. PC1 and PC2 explained 58.0 and 20.7% of variation, respectively. The PCA was calculated using proportions of saturated fatty acids (SFA), monounsaturated fatty acids (MUFA) and single polyunsaturated fatty acids detected in amounts above 2%.

Figure 3.

Change of the percentage of single polyunsaturated fatty acids (PUFA; 18:3n-3 and 20:5n-3) in three strains of Brachionus calyciflorus s.s. (‘Cornell’, ‘IGB’ and ‘USA’) and one strain of Brachionus fernandoi (‘No.2484’), when their food source was switched either from Monoraphidium minutum (Mon; rich in 18:3n-3) to PUFA-free Synechococcus elongatus (MonSyn; a,b) or from Nannochloropsis limnetica (Nan; rich in 20:5n-3) to S. elongatus (NanSyn; c,d). Data represent means ± s.d., number of replicates N = 3. (Online version in colour.)