Energy allocation in a diapausing copepod: a transcriptomics analysis

In highly seasonal and food-limited environments, diapause has been one of the strategies evolved in zooplankters to synchronize growth and reproduction to peaks in production. This type of dormancy, which involves developmental arrest, lowmetabolic activity, longer life span, and a delay in reproduction, includes a dependence on lipid stores to meet energetic needs of diapause and post-diapause reproduction. How capital breeders balance the energetic requirements of cellular function and the cost of reproduction in organisms that include a diapause remains poorly understood. Here, a gene expression study was used to investigate the relationships between energy utilization, cellular maintenance and oogenesis in the subarctic copepod Neocalanus flemingeri. After mating the non-feeding adult female enters a period of diapause prior to spawning ca. six months later. The capital needed to support the diapause and the reproductive programis acquired during the pre-adult stages, which co-occur with a short annual phytoplankton bloom. In N. flemingeri females, transcriptional pattern of genes involved in cellular homeostasis and metabolic pathways identified three major expression profiles coinciding with emergence from diapause and early oogenesis, mid to late oogenesis, and finally spawning and end-of-life. Post diapause and during early oogenesis, gene expression patterns suggested that females were metabolically active and basal cellular activities had resumed. This was followed by the down-regulation of genes involved in cellular homeostasis as the reproductive program progressed to mid and late oogenesis. As females started to spawn, genes involved in protein ubiquitination and programmed cell death became up-regulated. The data suggest that females match fecundity to available resources by limiting germline development to early post-diapause coincident with the up-regulation of genes involved in cellular homeostasis, glycolysis and lipid catabolism. This strategy decreases the risk of reproductive failure by assuring that oogonia can mature successfully.