Identification of molecular markers associated with starvation in female Calanus sinicus (Copepoda: Calanoida)

Evaluation of the physiological states of copepods can improve current understanding of the dynamics of zooplankton population and contribute to assessments of the health of trophic linkages in marine ecosystems. However, assessing the starvation status of copepods in situ using conventional methods is difficult because of spatial and temporal changes in food availability. Here, we analyzed gene expression to identify the molecular markers associated with starvation in the copepod Calanus sinicus from the western North Pacific Ocean. Differentially expressed genes (DEGs) were compared between starved and satiated copepods using highthroughput mRNA sequencing (RNA-Seq). Sixteen DEGs were identified. Nine of these DEGs were assigned to known functional genes associated with energy metabolism, egg production, and somatic growth, and therefore were evaluated by quantitative real-time polymerase chain reaction (qRT-PCR) as candidate markers for starvation. To evaluate the reliability of these candidate markers as indicators for starvation, copepods were given different food concentrations and fasted for various periods. Gene expression was highly sensitive to temporal and quantitative changes in food conditions. During starvation, the expression of NADH-dehydrogenase (related to energy metabolism) was upregulated and that of vitellogenin 2 (related to egg production) was downregulated compared to their expression in satiated copepods. As might be expected from such changes in expression, complete fasting significantly decreased egg production. Changes in NADH-dehydrogenase and vitellogenin 2 expression were therefore correlated with the degree of copepod starvation or food limitation. This information may help to assess potential reproductivity and predict egg production rates in copepods in their natural environment.