Award: OCE-1132567

Oceanic copepods in the family Calanidae are among the most abundant animals on the planet, and they serve a key role in marine food webs by transferring energy from phytoplankton all the way up the food chain to fish and whales. Just before reaching adulthood, many of these tiny marine crustaceans enter a type of hibernation called diapause to avoid adverse conditions in the upper ocean (e.g., warm temperatures, low food concentration, abundant predators). They migrate to depth and remain in diapause for months until conditions improve for them to migrate back to the surface, molt into adults, and begin reproducing. Curiously, some copepods skip diapause and molt directly into adults. The circumstances under which some copepods enter diapause and others skip diapause are very poorly known. As a result of this knowledge gap, predicting how populations of copepods change from year to year is impossible, and we therefore have limited ability to predict how changes in the environment from year to year will affect commercially important fish stocks and endangered baleen whales. Moreover, we are completely unable to predict how temperate, subarctic, and arctic ecosystems will be altered by climate change without a better understanding of the factors that trigger diapause. Our research was aimed at developing both (1) an understanding of the physiological processes that occur during preparation for diapause and during preparation for molting into the adult stage (i.e., skipping diapause), and (2) practical biomarkers that faithfully predict on which developmental path (preparing to diapause or to skip diapause) a copepod may be. We did this by examining two populations of the copepod Calanus finmarchicus, the dominant calanoid copepod in the North Atlantic Ocean, during laboratory and field research in Trondheim, Norway: a lab-reared population that skips diapause and a fjord population that enters diapause. By comparing gene expression between these two populations using state-of-the-art techniques (Illumina and qPCR), we were able to identify genes that "turn on" along each of these two developmental pathways. In particular, copepods that skip diapause show increased expression of genes associated with fat (lipid) accumulation (ELOV, FABP) early in the last stage of development before adulthood, and then expression of these genes reduces as they get closer to molting into an adult. Genes likely associated with molting (e.g., TORSO-like) show very high expression late in the last stage of development in preparation for the terminal molt, and therefore serve as excellent biomarkers of copepods that are skipping diapause. In contrast, wild copepods that are preparing for diapause show continued high expression of genes associated with lipid accumulation, which is essential for surviving the long periods of starvation associated with diapause. We identified several candidate genes and gene families that are expressed at much higher levels in the wild copepods than in the lab-reared copepods, and that also have roles in diapause in other crustaceans and insects. Future work will focus on confirming that these genes are consistently and specifically associated with diapause preparation in Calanus finmarchicus. Ultimately, these genes can be used to initiate novel studies about both the physiological and environmental factors that affect a copepodÆs "decision" to enter diapause. With this information, we will be able to better predict the fate of both copepod populations and the ecosystems in which they serve such vital roles. Throughout the project, we have taken the opportunity to train students at the undergraduate and graduate levels. In particular, a PhD student in the MIT/WHOI Joint program, Ms. Amalia Aruda Almada, came with us to Trondheim to study bacterial interactions with wild Calanus finmarchicus caught in Trondheimsfjord. She defended her Ph.D. thesis in December 2014 and was awarded a John A. Knauss Mar...