Protein and nucleic acid metabolism as proxies for growth and fitness of Oithona davisae (Copepoda, Cyclopoida) early developmental stages

Abstract

Despite the abundance of the marine copepod genus Oithona, little is known about its ecology and metabolism, especially regarding its early developmental stages. In this work, we combined two biochemical indices, already used in calanoid copepods, to estimate growth and fitness of Oithona davisae nauplii and copepodites: i) the specific aminoacyl-tRNA synthetases (spAARS) activity (proxy of protein synthesis rate) and ii) the RNA/DNA ratio (indicative of overall metabolic activity). We show here that the two analyses can be performed on the same organisms (samples), thus providing comparable and complementary information about the nauplii physiology. Our experiments provide a first insight into the variability of these parameters on O. davisae early developmental stages, showing that RNA/DNA ratio was more sensitive to starvation than the spAARS activity. A common relationship for nauplii and copepodites was observed between spAARS activity and somatic growth rates; however, RNA/DNA ratio relationships with both somatic growth rates and spAARS activity differed between the naupliar and copepodite stages. The study presented here contributes to the advancement of the study of small copepod nauplii physiology.