Oceanic copepods in the family Calanidae, such as Calanus finmarchicus, are among the most abundant animals on the planet, and they serve a key role in marine food webs by transferring energy from phytoplankton to higher trophic levels. The life history of these copepods has been well-studied, but fundamental questions remain about the regulation of an important period of dormancy called diapause. In the last juvenile stage of development, C. finmarchicus either proceed to the terminal molt (i.e., molt into adults) or vertically migrate to depth and initiate diapause. This divergence in developmental pathways has critical implications for C. finmarchicus population dynamics, but is difficult to study experimentally because C. finmarchicus, like all other copepods in the family Calanidae, do not reliably enter diapause in the laboratory. In addition, most temperate populations of calanoid copepods have multiple generations in a single year with variability in the timing of reproduction and development that causes significant heterogeneity in age structure. Thus, field sampling of these heterogeneous populations yields a mixture of copepods that are preparing for diapause, are preparing for the terminal molt, or are not yet preparing for either fate. Studies of diapause preparation in such populations are extremely difficult.
To enable direct investigation of the factors that influence diapause initiation, we require markers that reliably predict the fate of individual copepods (entry into diapause or continued maturation to adulthood) within heterogeneous populations. Fortunately, the fjord population of C. finmarchicus off the coast of Norway during the late spring is remarkably synchronous and is comprised of juvenile copepods that are all destined to undergo diapause. This project will use high-throughput 454 pyrosequencing to identify genes that change in expression as these copepods progress toward diapause. In collaboration with Norwegian researchers, the investigators will also rear copepods in a unique continuous culture and conduct additional transcriptional profiling to identify genes that change in expression as copepods prepare for the terminal molt. Comparison of gene expression patterns in the wild and cultured populations will enable the principal investigators to develop robust markers of diapauses preparation that can be used to study diapause initiation in more heterogeneous temperate populations.
Intellectual Merit: Despite decades of research, we are still ignorant of the processes that trigger diapause and are therefore unable to model the population dynamics of calanoid copepods for even a single generation. This is a long-standing and well-known gap in our understanding of marine ecosystems, and progress on this research problem could be transformative. By developing molecular markers to identify preparation for diapause, the investigators seek to enable novel physiological and ecological research that will ultimately identify both intrinsic and extrinsic factors that control entry into diapause. Their approach is based on an assumption that gene expression patterns in wild populations are sufficiently consistent to be used as a reliable indicator of diapause preparation. This fundamental assumption has yet to be tested; thus, this work is risky but with potentially high reward and suitable for an EAGER project.
Broader Impacts: This project will enable a highly complementary new collaboration between US and Norwegian researchers and the training of undergraduate and graduate students. The results will be communicated to broad audiences through social media. Development and application of biomarkers of diapause preparation will ultimately allow modelers to parameterize diapause and improve the ability of ecosystem models to forecast changes associated with human impacts to oceans and climate change
