Mechanistic Study Concerning The Impacts Of Ocean Acidification And Mercury Pollution On Marine Copepod Tigriopus Japonicus Under Multigenerational Exposure

Currently,the organisms in coastal areas are suffering from multiple environment stress due to global climate change and human pollution,which is exemplified by the co-stressors of OA and Hg pollution(hereafter coal burning is a primary causation).Expectedly,the co-stressors of OA and Hg pollution have been a common environmental disaster faced by coastal ecosystems at the global scale.Lots of studies have been carried out to investigate the individual effects of OA and Hg pollution on marine biota,however,only the works concerning the combined impacts from these two stressors can display environmental ecological significance more realistically.Nonetheless,very scare information has been presented about the response and adaptability of marine organisms in facing the coupled effects of OA and Hg pollution by now.Marine copepods are the main secondary producers and play one of the key nodes of material and energy transfer in marine ecosystems.Consequently,the copepods play a pivotal role in the marine food webs and also have very important ecological functions.In addition,marine copepods have been used as a good model species in marine stress ecology research.In this work,using Tigriopus japonicus as a model organism,we investigated metal accumulation and its impacts on seven important life history traits(survival,sex ratio,nauplius phase,development time,number of clutch,number of nauplii/clutch and fecundity/12 d)in the copepod under the long-term multigenerational exposure to OA and Hg pollution(F0-F3).Meanwhile,comparative quantitative proteomic profiling was conducted to screen and identify the proteomes associated with the copepod's responses to OA and Hg pollution(alone and combined).Our study was aimed to elucidate the mechanism of action for OA and Hg pollution on T.japonicas,as well as the response mechanism of the copepod.More importantly,this work was purposed to reveal the mechanism of action concerning the OA impacting on Hg toxicity in T.japonicus.The main findings are described as following:(1)In contrast to ambient condition,both single Hg treatment and the combined OA plus Hg exposure significantly enhanced Hg accumulation in the copepod at each generation,furthermore,the Hg accumulation increasing from FO to F3.Interestingly,when compared with Hg treatment alone,the combined exposure of OA plus Hg significantly decreased Hg concentrations in the copepod,suggesting that OA tended to reduce Hg accumulation in marine copepod.(2)The projected near-future OA level displayed negligible impacts on the development and reproduction of T.japonicas.However,Hg pollution significantly inhibited number of nauplii/clutch,.especially in the case of the F2 and F3 generations.Both the number of nauplii/clutch and fecundity/12 d were significantly increased by the combined exposure in contrast to single Hg treatment,suggesting that OA did significantly alleviate Hg toxicity,at least,to reproductive performance in the exposure copepod.(3)The projected near-future OA condition produced a significant proteome change of T.japonicus,mainly exemplified by the increased protein assimilation and proteolysis and decreased the proteins synthesis under reduced pH value.The changed proteome might probably be an adaptive energy reallocation strategy for T.japonicus in fighting against OA,that is,showing a strong phenotypic plasticity.Hg exposure caused a range of toxic events,e.g.,oxidative stress,cellular homeostasis dysregulation,decreased glutathione metabolism,as a consequence,which restrained reproductive capability in the treated copepods.Interestingly,under combination,the lysosome-autophagy machinery was initiated to remove the oxidative damaged biomolecules(e.g.,proteins and enzymes)in the copepods,and consequently decreased the restrained impact of Hg pollution on reproductive capacity in the copepods.(4)It should be emphasized that a common KEGG pathway of neuroactive ligand-receptor interaction was significantly enhanced under both single OA and Hg pollution,indicating that these two stressors potentially resulted in behavioral abnormality in the exposed copepods mainly via disturbance of neuronal activities.