Relating nucleic acid and protein indices to growth in Mysis relicta: ration, cycling temperature, and metabolism

Abstract

We investigated growth rate, nucleic acid (DNA, RNA) and protein indices and respiration in juvenile (8.5 to 12 mm total body length, 7 to 20 mg wet wt) and young adult (12 to 14 mm, 20 to 30 mg wet wt) Mysis relicta, as a function of temperature, body mass and molt stage in order to develop methods to assess condition or growth in the field. Mysids were exposed to either a preferred temperature (6.5°C) and 3 ration levels, or a range of constant and dielly-cycling (DC) temperatures with ad libitum feeding. Mysid growth parameters (specific rates of growth [SGR], respiration [M O 2 ], and RNA content cell -1 ) integrated the DC temperature experienced as averaged responses weighted by the time spent at each temperature. M O 2 peaked at 12.7°C on acute temperature exposure from 4.2°C. M O 2 compensation with prolonged temperature exposure occurred at mean diel temperatures ≤ 8.5°C. Mysids could not survive at 16°C even for 5 h d -1 . These results confirm behavioral observations of temperature preferences. RNA concentration in M. relicta increased with ration and decreasing temperatures. Protein:DNA ratio, %protein and SGR increased with ration and then plateaued. Protein:DNA ratio, %protein and DNA:weight ratio did not change with temperature with unlimited feeding. Forward, stepwise, multiple regression models for each experiment and the combined data accounted for 31 to 72% of variability in SGR. Our experimental data provide guidance, a preliminary temperature-correction factor for RNA, and benchmarks for use of nucleic acid and protein indices in assessing growth or condition of M. relicta in the field.

Field assessment of condition indices (nucleic acid and protein) in Mysis diluviana

“…Only juveniles in the inshore regions in 2004 and adult females in both the inshore and offshore regions in 2004 had a significantly lower protein content than in other years. Data from the laboratory growth experiments by Johannsson et al (2008) were also lower and similar to our 2004 values. The %protein data from Lake Ontario were variable, likely due to the process of 'growth by moulting', where individuals expand their new exoskeleton with water when they moult and then replace the water with tissue as they grow.…”

“…4H). Again, the experimental data indices of Johannsson et al (2008) were similar to the Lake Ontario indices for femals in 2001 and 2004 (Fig. 4E-H Inshore-offshore trends were clearly identified only in 2003 and 2004.…”

“…-Inshore, 2001-Offshore, 2003., and reanalyzed the data to produce comparable, adjusted means across the years. Finally, we compared our yearly indices from Lake Ontario with those from Lake Huron (October 2002) and with from laboratory experiments during which mysid growth rates were measured using the same methods as in the present study (Johannsson et al 2008). The Lake Huron data were included to provide a reference to mysid nucleic acid and protein indices from another field site because the higher growth rates observed in the field have not yet been attained in laboratory experiments.…”

“…If more active cells are larger, then there should be fewer of them per unit body weight, and therefore, DNA/dry wt and DNA/carbon content have been suggested as additional measures of condition (Bergeron 1997). In laboratory studies of Mysis diluviana growth rates under different conditions, Johannsson et al (2008) observed corresponding increases in RNA and protein relative to DNA and of protein relative to wet weight (%protein) with increases in growth rate, while the number of cells per unit of weight (DNA per unit wet weight) decreased. Changes in temperature can alter the relationship between RNA and growth rate.…”

Ecological impacts of invasive alien species along temperature gradients: testing the role of environmental matching

“…Water temperatures for the study system were obtained from the study itself, other studies on the same system, or online climatic databases. Diel migrators such as mysids experience a range of temperatures throughout the day (Beeton and Bowers 1982), and their overall feeding and growth rates are directly related to the amount of time they spend at each temperature (Johannsson et al 2008); therefore, we selected temperature measurements that best corresponded with the time and site at which the impact was measured.…”