Salinity Adaptation And Divergence Mechanisms Of Jinjiang Oyster (Crassostrea Ariakensis)

Crassostrea ariakensis(Bivalvia,Pterioida,Ostreidae)is mainly distributed in estuaries with salinity of 10-25.It often experienced large and rapid salinity fluctuations in its life history.Unlike other intertidal animals,oysters are attached to rocks and lack of mobility forces them to evolve many regulatory mechanisms to adapt to highly dynamic stress environments.The good tolerance of oyster to high or low salinity makes it an excellent research material for detecting stress response and adaptability.1.Differences in salt adaption and physiological responses among three wild populationsThe growth and salinity adaptability of the offspring of three wild populations(Binzhou,Guangzhou and Korea)were discussed.The lethal salinity and sub-lethal salinity of 14 days at high and low salinity were measured,which provided a basis for the standard of salinity treatment in subsequent physiological experiments.In the salinity response mechanism,we measured the levels of pyruvate kinase(PK),malondialdehyde(MDA),adenosine triphosphate(ATPase)and superoxide dismutase(SOD),which are related to energy metabolism and antioxidant regulation.The results showed that BZ population showed better growth and salt adaption in all three populations.In terms of energy metabolism,oysters reduce energy and energy demand by inhibiting aerobic metabolism,and begin to produce anaerobic metabolism to minimize ROS production and avoid body damage to adapt to extreme stress.Oysters maintain low levels of PK under low salt and hypoxia stress,which may be a compensatory mechanism under stress.In antioxidant regulation,the enhancement of free radical scavenging capacity of the body alleviates the degree of free radical attack on cells.In the face of high salinity changes,oysters need to mobilize more biological regulation functions and more energy,which is reflected in the increase of respiratory rate.These results provide a physiological understanding of the response of oyster to salinity stress.Salt-adaption populations were screened out from three wild populations,providing support for the construction of high-salt adaption variety.2.Molecular mechanism of salinity response under high salinityTo understand the adaptive capacity of oysters to salinity stress,we conducted transcriptome analysis to investigate the metabolic pathways of salinity stress effectors in oysters from two different geographical sites,namely at salinities of 16,23,and 30‰.We completed transcriptome sequencing of 18 samples and a total of 52,392 unigenes were obtained after assembly.Differentially expressed gene(DEG)analysis and weighted gene correlation network analysis(WGCNA)were performed using RNASeq transcriptomic data from eye-spot larvae at different salinities and from different populations.The results showed that at moderately high salinities(23 and 30‰),genes related to osmotic agents,oxidation-reduction processes and related regulatory networks of complex transcriptional regulation and signal transduction pathways dominated to counteract the salinity stress.Moreover,there were adaptive differences in salinity response mechanisms,especially at high salinity,in oyster larvae from different populations.These results provide a framework for understanding the interactions of multiple pathways at the system level and for elucidating the complex cellular processes involved in responding to osmotic stress and maintaining growth.Furthermore,the results facilitate further research into the biological processes underlying physiological adaptations to hypertonic stress in marine invertebrates and provide a molecular basis for our subsequent search for high salinity-tolerant populations.