Effect of temperature and dietary elemental composition on RNA/protein ratio in a rotifer

1. Temperature and the elemental composition of food are key regulators of consumer growth rate, yet the knowledge on how these factors interact is scarce. In this study, we addressed this issue by using the rotifer Brachionus calyciflorus as a model organism. 2. Rotifers were raised at four different temperatures under a range of C/P and C/N ratios in their food and assessed the responses by analysing somatic RNA/protein ratios as a marker of growth rate. 3. Both N- and P-limited algae restricted the growth rates of rotifers. The interaction between C/P ratio of a given algae and temperature demonstrated that P limitation became intensified with increasing temperature. 4. Animals that were relieved from N limitation increased their RNA/protein ratio, as did animals fed on constant C/N ratio but with P-enriched food. This illustrates a mutual dependency and interaction between N and P in the protein synthesis by up-regulating the biosynthetic machinery, and that even while the effect of N limitation was more pronounced, P limitation was also potentially important in this species. 5. Our results provide evidence that over the tested range of temperature and food qualities, nutrient limitation in these animals was more important than the temperature effect. We also found, however, that increasing temperature can shift from P to N limitation in the consumer.