RNA:DNA ratios as a proxy of egg production rates of Acartia

Abstract

Estimates of copepod secondary production are of great importance to infer the global organic matter fluxes in aquatic ecosystems and species-specific responses of zooplankton to hydrologic variability. However, there is still no routine method to determine copepods secondary production in order to eliminate time consuming experimental analyses. Therefore, we determined whether there is a correlation between Egg Production Rates (EPR) and RNA:DNA ratios of Acartia, by measuring their seasonal and spatial variability and the influence of environmental factors for Acartia sp. collected in the the Guadiana river estuary. EPR of A. tonsa was positively related with chlorophyll a concentration, freshwater inflow and biomass of dinoflagellates, while A. clausi was only related to dinoflagellates. Dinoflagellates seem to be the optimal food item influencing the reproduction of both Acartia species in the studied area. The biochemical index RNA:DNA was positively related to EPR, indicating that it is a good proxy of copepod production and a promising method to use in the future to estimate secondary production.

Plankton community and copepod production in a temperate coastal lagoon: What is changing in a short temporal scale?

“…They obtained higher values during September (23.9 µg C m -3 day -1 ) which are comparable to what was found in the present study during the same season (average: 42.6 ± 59 µg C m -3 day -1 ). Moreover, the summer production of A. clausi females in the adjacent coastal waters of Guadiana river estuary was higher than in Ria Formosa but also comparable to what was found in the present study (average values of 98.8 ± 84.3 µg C m -3 day -1 ; Cruz et al, 2017). These results suggest that there is a potential considerable flow of energy and matter through the planktonic food web, especially to the early stages of the important fisheries resources (e.g.…”

“…: Nakata et al, 1994;Calanus sinicus: Ning et al, 2013; Acartia J o u r n a l P r e -p r o o f Journal Pre-proof spp. : Cruz et al, 2017) have already shown this significant relationship between the two growth indices. This result is adding more evidence for the replacement of a more laborious and timeconsuming method such as the egg production rate determination with the RNA:DNA ratio methodology.…”

“…Saiz et al (1998) also found a temperature dependency relationship between the EPR of A. grani and the RNA:DNA index. On the other hand, some studies did not find any correlation between temperature and the ecophysiological index (Gorockova, 2003;Ning et al 2013;Cruz et al, 2017). The fact that there was no food limitation during the sampling period probably induced a more evident influence of temperature on the biochemical ratio.…”

“…However, in the last decades, biochemical approaches such as the determination of RNA:DNA ratio have been developed to assess the physiological condition of copepods (Chícharo and Chícharo, 2008), as an indicator of growth (Elser et al, 2000;Wagner et al, 2001), nutritional condition (Wagner et al, 1998;Vehmaa et al, 2012), dormant condition (Kobari et al, 2013) and egg viability (Hogfors et al, 2011). Additionally, the RNA:DNA ratio has been shown to be correlated with female egg production (Nakata et al, 1994;Saiz et al, 1998;Gorokhova, 2003;Cruz et al, 2017), making it a potential alternative method for the estimation of production, with several advantages over the traditional techniques such as sensitivity, precision and repeatability.…”

A glimpse into the trophic ecology of deep‐water sharks in an important crustacean fishing ground

“…Among the most used condition indices at the organism level in marine ecology are the nucleic acid‐derived indices, such as RNA/DNA values (RD). This ratio has been successfully applied as an indicator of growth ( e.g ., Bulow, 1987; Caldarone et al ., 2003; Tavares et al ., 2006), nutritional condition ( e.g ., Alves et al ., 2020; Chícharo et al ., 2003; Chícharo & Chícharo, 1995), productivity ( e.g ., Cruz et al ., 2017), health status ( e.g ., Tavares et al ., 2006) and as an indicator of natural or anthropogenic impacts in marine populations and communities (Chícharo & Chícharo, 2008; Müller et al ., 2020). The RD values provide a short‐term measure of nutritional condition (1–3 days Buckley et al ., 1999), based on the fact that DNA concentrations within individual cells remain relatively constant (Wallace, 1992) while RNA concentrations increase as protein synthesis increases (Buckley et al ., 1999).…”