Capital Breeding in a Diapausing Copepod: A Transcriptomics Analysis
Vittoria Roncalli, Matthew Cieslak, Russell R. Hopcroft, Petra H. Lenz
Abstract
Capital breeders must balance the energetic requirements of cellular function and the cost of reproduction in organisms. The subarctic copepod Neocalanus flemingeri, a small planktonic crustacean, depends on a short annual phytoplankton bloom to acquire the energy needed to support a non-feeding female adult that enters a period of diapause prior to spawning five to seven months later. After emergence from diapause, the reproductive program takes two-months starting with germline development. The relationships between energy utilization, cellular maintenance and oogenesis were investigated through gene expression profiling. The sequential up- and down-regulation of genes involved in cellular maintenance and metabolic pathways coincided with four developmental groups: diapause, emergence from diapause and early oogenesis, mid to late oogenesis, and finally spawning and end-of-life. Up-regulation of genes involved in cellular homeostasis, glycolysis and lipid catabolism as well as germline development characterized the transition from diapause to post-diapause. The down-regulation of genes involved in cellular homeostasis coincided with the up-regulation of genes related to mid-late oogenesis and protein degradation. As females started to spawn, genes involved in protein ubiquitination and programmed cell death became up-regulated. Energy allocation and utilization is highly dynamic in N. flemingeri during the non-feeding period and it is linked to the provisioning and maturation of eggs through lipid catabolism and autophagy. The data suggest the presence of a mechanism that regulates fecundity to match the availability of stored resources. Such a mechanism would minimize reproductive failure when resources and contribute to the resilience of the species.