Biology subjects

Maas, A. E.

Publications and source records attributed to Maas, A. E..

4 recordsLinked to original sources

bioRxiv2025

Hypoxia adaptation shapes genomic architecture and vertical niche transitions in copepods

Oxygen Minimum Zone (OMZ) expansion is a major challenge to marine ecosystems and associated zooplankton. Calanoid copepods include lineages that tolerate hypoxia and exhibit functional traits such as diel vertical migrations towards, or dormancy within, hypoxic mesopelagic zones. However, the evolutionary origins and molecular drivers of these functional traits remain unclear. Herein, we integrate a time-calibrated phylotranscriptomic tree of 50 copepod species with ancestral trait reconstruction, gene family copy number variation, and palaeoceanographic data to infer the evolutionary timing and ecological drivers of hypoxia adaptation. Our results support the following scenario: 1. Post-embryonic dormancy probably originated in calanoid ancestors, accompanied by widespread gene expansions involving hypoxia-response pathways as well as lipid and amino acid metabolisms. 2. Mesopelagic colonisation by calanoid lineages likely occurred during the Ordovician deep-sea oxygenation event. 3. During the Carboniferous deep-sea deoxygenation, a secondary habitat shift would have occurred toward shallower waters and embryonic dormancy, and as well as a contraction of the size of gene families in the Diaptomoidae. We further analysed the transcriptomic response of Eucalanus hyalinus from the Benguela upwelling OMZ versus surface waters, and identified a coordinated response involving extracellular matrix remodelling, amino acid recycling for anaerobic energy and antioxidant production as well as triglycerides to wax ester conversion. Ka/Ks analysis of gene family expansions upstream (proteolysis, transport) and downstream (antioxidant biosynthesis) of core metabolic pathways suggested purifying selection on dosage-sensitive genes. Together, these results link palaeoclimate change to lineage-specific genome evolution patterns supporting copepod adaptation to oxygen limitation.

evolutionary biology↗

bioRxiv2023

Sea butterflies in a pickle: Reliable biomarkers and seasonal sensitivity of pteropods to ocean acidification in the Gulf of Maine

The passive dissolution of anthropogenically produced CO2 into the ocean system is reducing ocean pH and changing a suite of chemical equilibria, with negative consequences for some marine organisms, in particular those that bear calcium carbonate shells. Although our monitoring of these chemical changes has improved, we have not developed effective tools to translate observations, which are typically of the pH and carbonate saturation state, into ecologically relevant predictions of biological risks. One potential solution is to develop bioindicators: biological variables with a clear relationship to environmental risk factors that can be used for assessment and management. Thecosomatous pteropods, a group of pelagic shelled marine gastropods, whose biological responses to CO2 have been suggested as potential bioindicators of OA owing to their sensitivity to acidification in both laboratory and the natural environment. Using five CO2 exposure experiments, occurring across 4 seasons and running for up to 15 days, we describe a consistent relationship between saturation state, shell transparency, and duration of exposure, as well as identify a suite of genes that could be used for biological monitoring. We clarify variations in thecosome responses due to seasonality, resolving prior uncertainties and demonstrating the range of their phenotypic plasticity. These biomarkers of acidification stress can be implemented into ecosystem models and monitoring programs in regions where pteropods are found, while the approach will serve as an example for other regions on how to bridge the gap between point-based chemical monitoring and biologically relevant assessments of ecosystem health. Summary StatementDespite seasonal variability, pteropods exposed to acidification over multiple seasons reveal consistent patterns in gene expression and shell condition that can be used as bioindicators of ocean acidification stress.

physiology↗

bioRxiv2023

Quantitative analysis of food web dynamics in a low export ecosystem

Food webs trace the flow of organic matter and energy among producers and consumers; for pelagic marine food webs, network complexity directly influences the amount and form of carbon exported to the deep ocean via the biological pump. Here we present a synoptic view of mixed layer food web dynamics observed during the late summer 2018 EXport Processes in the Ocean from Remote Sensing (EXPORTS) field campaign in the subarctic Northeast Pacific at the long-running time-series site, Ocean Station Papa. Carbon biomass reservoirs of phytoplankton, microzooplankton, and bacterioplankton, were approximately equal while mesozooplankton biomass was 70% lower. Live organisms composed [~]40% of the total particulate organic carbon within the mixed layer: the remainder was attributed to detritus. Rates of carbon transfer among reservoirs indicated production and assimilation rates were well balanced by losses, leaving little organic carbon available for export. The slight positive net community production rate generated organic carbon that was exported from the system in the form of food web byproducts, such as large fecal pellets generated by mesozooplankton. This characteristically regenerative food web had relatively slow turnover times with small-magnitude transfers of carbon relative to standing stocks that occurred amidst a high background concentration of detrital particles and dissolved organic matter. The concurrent estimation of food web components and rates revealed that separated processes dominated the transfer of carbon within the food web compared to those that contributed to export. Plain Language SummaryThe biological carbon pump drives a downward flux of organic matter from the sunlit surface ocean to the vast ocean interior. Ecological interactions in the surface ocean directly affect the amount and type of carbon that is exported to the deep ocean. In this study, we present a synthesis of the late summer mixed layer food web in the Northeast Pacific that was extensively characterized during the 2018 EXport Processes in the Ocean from Remote Sensing (EXPORTS) field campaign. We found the majority of carbon was recycled within the mixed layer by microbes through multiple transfers between producers and consumers. Larger organisms, mesozooplankton and salps, only consumed a small amount of carbon but through the formation of sinking fecal pellets were the main mechanism of transporting carbon out of the system. The study highlights the need to concurrently study microbial and large organism dynamics to develop a predictive understanding of the fate of organic carbon in the oceans. Key PointsO_LIThe microbial loop dominated carbon flow in the late summer mixed layer food web of the North Pacific, most net production was respired leaving little carbon available for export. C_LIO_LIActive production and consumption of organic carbon occurred amid a high background of detrital particulate organic carbon (58% of total) with slow turnover time, 66 d. C_LIO_LIMesozooplankton which had relatively minor carbon consumption rates created the majority of export production due to efficient repackaging of consumed material. C_LI

ecology↗

bioRxiv2020

Seasonal variation in physiology and shell condition of the pteropod Limacina retroversa in the Gulf of Maine relative to life cycle and carbonate chemistry.

Natural cycles in the seawater partial pressure of carbon dioxide (CO2) in the Gulf of Maine, which vary from [~]250-550 {micro}atm seasonally, provide an opportunity to observe how the life cycle and phenology of the shelled pteropod Limacina retroversa responds to changing food, temperature and carbonate chemistry conditions. Distributional, hydrographic, and physiological sampling suggest that pteropod populations are located in the upper portion of the water column (0-150 m) with a maximum abundance above 50 m, allowing them to generally avoid aragonite undersaturation. Gene expression and shell condition measurements show, however, that the population already experiences biomineralization stress in the winter months even when aragonite is slightly oversaturated, reinforcing the usefulness of this organism as a bio-indicator for pelagic ecosystem response to ocean acidification. There appear to be two reproductive events per year with one pulse timed to coincide with the spring bloom, the period with highest respiration rate, fluorescence, and pH, and a second more extended pulse in the late summer and fall. During the fall there is evidence of lipid storage for overwintering, allowing the second generation to survive the period of low food and aragonite saturation state. Based on these observations we predict that in the future pteropods will likely be most vulnerable to changing CO2 regionally during the fall reproductive event when CO2 concentration already naturally rises and there is the added stress of generating lipid stores.

ecology↗