Award: OCE-1459826

The research produced data key to assessing the resilience to environmental stress of the highly productive fisheries in the high-latitude North Pacific. The focus of the study was on lipid-rich copepods, which are an important food source for larval fish and forage fishes. A critical phase in the life cycle of these copepods is the period of dormancy (diapause) that precedes reproduction in late winter. Understanding diapause and emergence from diapause is essential for predicting how the copepods might be impacted by future environmental perturbations. During a 4-year program of oceanographic cruises during the fall, plankton were collected from below 400-meters depth in Prince William Sound in Alaska and offshore in the Gulf of Alaska. Adult females of the target organism, the subarctic marine copepod Neocalanus flemingeri, were live-sorted for laboratory incubations for physiological profiling, size and lipid volume measurements and total egg production. A separate set of samples from different depth layers was preserved and counted. Physiological profiling was done by monitoring the messages, the "mRNA transcripts," produced by the copepod's genes to control its life processes using a state-of-the-art molecular biological approach. The first step was to generate a gene reference through a shotgun assembly of millions of short-sequence reads produced from the mRNA. This reference transcriptome was then used to measure the expression level (amount of message) of each gene in samples collected during different years and at different time points after females emerged from diapause. One discovery was that during diapause the N. flemingeri females express genes that allow them to conserve energy, lengthen their lifespan, arrest cellular processes and protect them from oxidative stress. Diapause and post-diapause females represent two distinct physiological phases as determined from gene expression profiles. The transition from one phase to the next is a lengthy step-wise "post-diapause" restart process before egg development ("oogenesis") becomes the dominant process at one-week post-diapause. In addition, this study has uncovered an orchestrated and complex sequence of changes in gene expression that start almost immediately after the diapause termination stimulus through the early post-diapause phase. These findings give rise to the hypothesis that these sequential changes in gene expression control a universal mechanism that fully terminates diapause before an organism can resume its developmental program. However, even after the transition is complete there is a lengthy post-diapause phase, which is necessary to complete the reproductive program. After emergence from diapause, it takes six to seven weeks before females release the first clutch of eggs. Once spawning is complete, females die, and the population is composed of newly-hatched larval copepods ("nauplii"), which depend on the spring phytoplankton bloom to grow. As hypothesized, preliminary evidence suggests that nauplii can themselves enter a state of physiological quiescence while food resources are low, resuming growth after phytoplankton (algae) levels increase. Quiescence in the nauplii bore some of the molecular signatures of diapause, giving better insight into its mechanism and ultimately to the species’ resilience to environmental variability. There was evidence that during a year of very low phytoplankton abundances, although females were still able to complete diapause and the post-diapause reproductive program, overall fecundity was lower. In addition, there were significant interannual differences in gene expression profiles of females in diapause suggesting that growth conditions affected this phase. This study is closing a knowledge gap in the mechanistic understanding of how an organism restarts physiological processes after prolonged diapause to complete its life cycle. The research has furthered the long-standing goal of biological oceanographers of understanding dormancy and its role in controlling population cycles in marine copepods. It has introduced new technologies for studying dormancy in adults and nauplii. These new insights will contribute to predictions and preparation for anticipated environmental changes impacting vulnerable fisheries in a region that currently accounts for over half of all fish produced for consumption in the United States and a third of its economic value. The collaborative project provided training opportunities for two post-doctoral fellows, a graduate student, four undergraduate students and two post-baccalaureate fellows from the University of Hawaiʻi at Mānoa and additional students at the University of Alaska Fairbanks. Trainees from Hawaiʻi joined research cruises in the Gulf of Alaska and participated in laboratory experiments at the University of Alaska Fairbanks. One undergraduate student was from an under-represented group and another was a former NIH Maximizing Access to Research Careers fellow. The project supported the development and implementation of a new graduate course in bioinformatics of non-model species. Outreach in Hawaiʻi and Alaska occurred through special events like the large biennial Open House in Hawaiʻi (2015, 2017, 2019) and presentations and laboratory tours in Seward and Homer, Alaska (2018, 2019). The research was featured in a children’s book published in 2020 (Into the Deep: Science, Technology, and the Quest to Protect the Ocean by Christy Peterson, Lerner Publishing Group). Last Modified: 03/08/2021 Submitted by: Russell R Hopcroft