Variations in copepod proteome and respiration rate in association with diel vertical migration and circadian cycle

Author Posting. © University of Chicago, 2018. This article is posted here by permission of University of Chicago for personal use, not for redistribution. The definitive version was published in Biological Bulletin 235 (2018): 30-42, doi:10.1086/699219.The diel vertical migration of zooplankton is a process during which individuals spend the night in surface waters and retreat to depth during the daytime, with substantial implications for carbon transport and the ecology of midwater ecosystems. The physiological consequences of this daily pattern have, however, been poorly studied beyond investigations of speed and the energetic cost of swimming. Many other processes are likely influenced, such as fuel use, energetic trade-offs, underlying diel (circadian) rhythms, and antioxidant responses. Using a new reference transcriptome, proteomic analyses were applied to compare the physiological state of a migratory copepod, Pleuromamma xiphias, immediately after arriving to the surface at night and six hours later. Oxygen consumption was monitored semi-continuously to explore underlying cyclical patterns in metabolic rate under dark-dark conditions. The proteomic analysis suggests a distinct shift in physiology that reflects migratory exertion and changes in metabolism. These proteomic analyses are supported by the respiration experiments, which show an underlying cycle in metabolic rate, with a peak at dawn. This project generates molecular tools (transcriptome and proteome) that will allow for more detailed understanding of the underlying physiological processes that influence and are influenced by diel vertical migration. Further, these studies suggest that P. xiphias is a tractable model for continuing investigations of circadian and diel vertical migration influences on plankton physiology. Previous studies did not account for this cyclic pattern of respiration and may therefore have unrepresented respiratory carbon fluxes from copepods by about 24%.Funding for ET-S was provided by a Training Grant from the National Institutes of Health (T32 HG00035), and proteomics work was supported in part by the University of Washington’s Proteomics Resource (UWPR95794). Funding was provided by Simon’s Foundation International as part of the BIOSSCOPE project.2019-08-1

Transitioning global change experiments on Southern Ocean phytoplankton from lab to field settings: insights and challenges

The influence of global change on Southern Ocean productivity will have major ramifications for future management of polar life. A prior laboratory study investigated the response of a batch-cultured subantarctic diatom to projected change simulating conditions for 2100 (increased temperature/CO2/irradiance/iron; decreased macronutrients), showed a twofold higher chlorophyll-derived growth rate driven mainly by temperature and iron. We translated this design to the field to understand the phytoplankton community response, within a subantarctic foodweb, to 2100 conditions. A 7-d shipboard study utilizing 250-liter mesocosms was conducted in March 2016. The outcome mirrors lab-culture experiments, yielding twofold higher chlorophyll in the 2100 treatment relative to the control. This trend was also evident for intrinsic metrics including nutrient depletion. Unlike the lab-culture study, photosynthetic competence revealed a transient effect in the 2100 mesocosm, peaking on day 3 then declining. Metaproteomics revealed significant differences in protein profiles between treatments by day 7. The control proteome was enriched for photosynthetic processes (c.f. 2100) and exhibited iron-limitation signatures; the 2100 proteome exposed a shift in cellular energy production. Our findings of enhanced phytoplankton growth are comparable to model simulations, but underlying mechanisms (temperature, iron, and/or light) differ between experiments and models. Batch-culture approaches hinder cross-comparison of mesocosm findings to model simulations (the latter are akin to “continuous-culture chemostats”). However, chemostat techniques are problematic to use with mesocosms, as mesozooplankton will evade seawater flow-through, thereby accumulating. Thus, laboratory, field, and modeling approaches reveal challenges to be addressed to better understand how global change will alter Southern Ocean productivity

Physiological responses of a Southern Ocean diatom to complex future ocean conditions

A changing climate is altering many ocean properties that consequently will modify marine productivity. Previous phytoplankton manipulation studies have focused on individual or subsets of these properties. Here, we investigate the cumulative effects of multi-faceted change on a subantarctic diatom 'Pseudonitzschio multiseries' by concurrently manipulating five stressors (light/nutrients/C0₂/temperature/iron) that primarily control its physiology, and explore underlying reasons for altered physiological performance. Climate change enhances diatom growth mainly owing to warming and iron enrichment, and both properties decrease cellular nutrient quotas, partially offsetting any effects of decreased nutrient supply by 2100. Physiological diagnostics and comparative proteomics demonstrate the joint importance of individual and interactive effects of temperature and iron, and reveal biased future predictions from experimental outcomes when only a subset of multi-stressors is considered. Our findings for subantarctic waters illustrate how composite regional studies are needed to provide accurate global projections of future shifts in productivity and distinguish underlying species-specific physiological mechanisms

Integrating Discovery-driven Proteomics and Selected Reaction Monitoring To Develop a Noninvasive Assay for Geoduck Reproductive Maturation

Geoduck clams (<i>Panopea generosa</i>) are an increasingly important fishery and aquaculture product along the eastern Pacific coast from Baja California, Mexico, to Alaska. These long-lived clams are highly fecund, although sustainable hatchery production of genetically diverse larvae is hindered by the lack of sexual dimorphism, resulting in asynchronous spawning of broodstock, unequal sex ratios, and low numbers of breeders. The development of assays of gonad physiology could indicate sex and maturation stage as well as be used to assess the status of natural populations. Proteomic profiles were determined for three reproductive maturation stages in both male and female clams using data-dependent acquisition (DDA) of gonad proteins. Gonad proteomes became increasingly divergent between males and females as maturation progressed. The DDA data were used to develop targets analyzed with selected reaction monitoring (SRM) in gonad tissue as well as hemolymph. The SRM assay yielded a suite of indicator peptides that can be used as an efficient assay to determine geoduck gonad maturation status. Application of SRM in hemolymph samples demonstrates that this procedure could effectively be used to assess reproductive status in marine mollusks in a nonlethal manner