Biochemical proxies for growth and metabolism in Acartia bifilosa (Copepoda, Calanoida)

Abstract

Biochemical proxies are becoming increasingly common for growth assessment in zooplankton. Their suitability is often unknown, however, and proper calibration is lacking. We investigated correlations between physiological variables (ingestion, egg production, and respiration rates) and biochemical indices related to protein synthesis (RNA content, RNA:DNA ratio, RNA:protein ratio, and protein specific aminoacyl-tRNA synthetases [spAARS] activity) in copepods Acartia bifilosa exposed to different algal concentrations (0-1200 µg C L -1). All variables assayed increased with increasing food concentration either linearly (spAARS) or nonlinearly (all other variables). Egg production and ingestion rates were significantly and positively correlated with RNA content and RNA:protein ratio, whereas correlations with spAARS and RNA:DNA ratio were weaker or nonsignificant. However, when RNA:DNA ratio and spAARS activity were used as predictors of ingestion, together they had higher explanatory value than did either variable separately. As there were substantial differences in saturating food concentrations among the assayed variables, applicability of biomarkers as proxies of physiological rates will be more reliable if restricted to the nonsaturated phase of the functional response of either variable, unless both variables saturate simultaneously. These findings contribute to methodology of zooplankton growth assessment and to our understanding of biochemical processes underlying growth and metabolism in copepods.

Nucleic acid ratio as a proxy for starvation of coastal and pelagic copepods in the North Pacific Ocean

“…4). These findings are consistent with previous results using copepod cultures, where the ratios showed a negative correlation to temperature (Ota & Landry 1984, Wagner et al 2001) and a positive correlation to food concentration (Ota & Landry 1984, Wagner et al 1998, Gusmão & McKinnon 2009, Holmborn et al 2009). As suggested by Wagner et al (1998Wagner et al ( , 2001, the positive and negative correlations are likely to be due to enhanced chemical reactions with lower enzyme or RNA concentrations at higher temperature and increased substrates for protein synthesis, respectively.…”

“…Among the biochemical approaches, nucleic acid-based indices have been most commonly applied in various metazoan species as proxies of individual physiological condition, reproductive activity and somatic growth (see Yebra et al in press). The nucleic acid ratio (RNA/ DNA) is suggested as a proxy of feeding history, including starvation, because nucleic acids are functioning in the first steps of protein synthesis and cellular contents of nucleic acids vary with protein synthesis activity (e.g., Gorokhova & Kyle 2002, Speekmann et al 2007, Holmborn et al 2009). Starvation is considered to increase copepod mortality risks due to the reduction of their swimming activity (Mackas & Burns 1986).…”

Trade-Offs between Predation Risk and Growth Benefits in the Copepod Eurytemora affinis with Contrasting Pigmentation

“…This ratio was used as a proxy for overall metabolic activity in the copepods [39]. The nucleic acid concentrations were measured in both field samples preserved in RNA later (5 stations, LL6 excluded; Table 1) and those collected upon termination of the grazing experiment (6 replicates).…”

Indirect consequences of hypolimnetic hypoxia on zooplankton growth in a large eutrophic lake

“…Daph nia mendotae samples were removed from RNA Later ™, rinsed with RNAse-free water, and homo genized in extraction buffer (50 µl, 1% sarcosyl in TE buffer) (Höök et al 2008). Samples underwent a repeated sequence (n = 3) of an ultrasound bath (30 s) and an ice bath (1 min) (Holmborn et al 2009), and were shaken for 2 h at room temperature (Höök et al 2008). The subsamples (5 µl) and TE buffer (65 µl) then were transferred to a microplate well.…”