Physiological And Molecular Mechanism Involved In Marine Copepod Tigriopus Japonicus In Response To Microplastics Multigenerational Exposure

Plastic waste accounts for 60-90%of the total amount of marine waste,which contains a large number of plastic particles with a diameter of less than 5 mm,namely microplastics.Given their small dimensions,ubiquitous nature and large quantity,microplastics can be ingested by marine organisms and,in the end,have adverse effects on marine ecosystem.Most microplastics stress studies are mainly focused on microplastics accumulation and the:ir adverse physiological effects in marine organisms,yet little information is available for giving a mechanistic understanding concerning the microplastics effect;also,most microplastics exposure experiments are partially focused on short-term or single-generation effects under far more than environmentally-realistic-concentration exposure.Correspondingly,any molecular investigation concerning microplastics effect on marine animals under the long-term multigenerational exposure to environmentally realistic concentrations is particularly and urgently important,as it can enable us to accurately perform the ecological risk assessment and establish the sea water benchmark for microplastics pollution in marine environment.It should be noted that marine copepods are extremely important links in marine classic food network and play a role in the transfer of materials and energy in marine ecosystem;changes in community of copepods will probably compromise the whole marine ecosystem.Here we firstly used an ecologically important marine copepod Tigriopus japonicus as a model species to explore the ingestion of copepods on microplastics(3-day ingestion test);after confirming the ingestion of microplastics by copepods,we then investigated the effects of environmentally-relevant level microplastics pollution(concentrations of 0.023 and 0.23 mg/L in seawater solutions)on the marine copepod under two-generation exposure(F0-F1).To explore the copepod's transgenerational effect in response to microplastics,all the animals were subsequently recovered in clean seawater for one generation(F2).During exposure,seven life-history traits including survival rate,development time of nauplius phase,development time to maturation,number of clutches,number of nauplii/clutch,and fecundity were measured for each generation.In particular,the proteome profiles were analyzed for the F1 and F2 copepods under the control and 0.23 mg/L microplastics treatment so as to reveal the coping mechanism and survival strategy of marine copepod in against microplastics pollution.The followings are the main findings:(1)Short-term ingestion tests showed that microplastics could be ingested by the copepods T.japonicus under both exposures(0.023 and 0.23 mg/L).The average microplastics bioaccumulation in T.japonicus was approximately 2 particles/copepod and 38 particles/copepod,respectively,for the 0.023 and 0.23 mg/L treatments.Although the treated copepods consumed approximately 40%microplastics in seawater.most of them were likely present in fecal particles.(2)After two-generations exposure to microplastics,the low microplastics treatment(0.023 mg/L)negligibly affected the seven life traits in T.japonicus for F0-F1.As for the high treatment(0.23 mg/L),microplastics had adverse effects on important life history traits,e.g.,survival rate and reproduction(number of nauplii/clutch,and fecundity/12 d).Interestingly,the compromised traits were completely regained during one generation recovery(F2),highlighting that the two-generational exposure to microplastics did not produce transgenerational effect in the copepod species at the phenotypic level(3)The proteomic analysis demonstrated that microplastics effect significantly increased many biosynthesis processes(e.g.,ribosome,gene expression,peptide biosynthetic process,translation and cellular protein metabolic process).and in turn.probably reduced energy store due to the energetic trade-off;hence compromising survival and reproduction of the treated copepods of the exposure generation(F1).As for the recovery generation(F2).the two-generational effect of microplastics in copepods had significant transgenerational proteome plasticity as demonstrated b)increased expression of cuticle formation,energy metabolism and stress-related defense pathway,which accounts for regaining of the compromised phenotypic traits during recovery(4)Interestingly,the two-generational effect of microplastics in copepods had significant transgenerational proteome plasticity,although it did not produce significant transgenerational effect at the phenotypic level.Within-generation effect of microplastics mainly increased the biosynthesis process at the proteomic level,while the transgenerational proteome plasticity mainly enhanced energy production and stress-related defense pathway.Compared with within-generation proteomic response,the copepod displays stronger transgenerational proteome plasticity in response to microplastics pollution.Taken together,the transgenerational proteome plasticity may play an impor'tant role in against microplastics exposure and probably render the copepods showing high resilience.Overall,this study provides a molecular mechanism on microplastics effect in marine copepod at translational level and also a new understanding of the long-term multi-generational effect of the environmentally relevant-level microplastics exposure on marine organisms.