International Journal of Marine Science, 2024, Vol.14, No.5, 295-303 http://www.aquapublisher.com/index.php/ijms 301 7.2 Evolutionary genomic responses to pollution and ocean acidification Ascidians, like other marine organisms, face significant threats from pollution and ocean acidification. The study on the marine copepod Acartia tonsa provides insights into how marine species can adapt to multiple stressors, including warming and acidification, through polygenic responses targeting cellular homeostasis and stress response mechanisms (Brennan et al., 2021). Similarly, the rapid adaptation of killifish to polluted environments through introgression of toxicant-resistant genes from a related species underscores the potential for genetic variability to facilitate evolutionary rescue in Ascidians facing pollution (Oziolor et al., 2019). The genomic analysis of the invasive Ascidian Molgula manhattensis revealed significant genetic differentiation driven by local environmental factors, particularly salinity, indicating that pollution and other environmental stressors can drive adaptive divergence in Ascidianpopulations (Chen et al., 2021). 7.3 Molecular mechanisms underpinning resistance to environmental stressors The molecular mechanisms that enable Ascidians to resist environmental stressors are diverse and complex. Proteomic studies on the stolon of Ciona robusta have identified key pathways involved in stress response, including cytoskeleton stability, signal transduction, and posttranslational modifications, which are crucial for maintaining structural integrity and activating stress responses under temperature and salinity stress (Li et al., 2021). Additionally, alternative splicing (AS) mechanisms play a significant role in the phenotypic plasticity of Ascidians, with species-specific and environmental context-dependent AS responses observed in Ciona robusta and Ciona savignyi, highlighting the importance of AS in rapid adaptation to environmental changes (Huang et al., 2023). The interplay between genetic and epigenetic variations also contributes to local adaptation, as seen in Ciona intestinalis populations, where DNA methylation patterns driven by local environments complement genetic adaptations, enhancing the rapid adaptive capacity of Ascidians (Chen et al., 2022). Acknowledgments I appreciate Dr H.Y. Wang for her assistance and thank the anonymous reviewers for their insightful comments and suggestions that improved the manuscript. Conflict of Interest Disclosure The author affirms that this research was conducted without any commercial or financial relationships that could be construed as a potential conflict of interest. References Brennan R.S., deMayo J.A., Dam H.J., Finiguerra M., Baumann H., Buffalo V., and Pespeni M.H., 2021, Experimental evolution reveals the synergistic genomic mechanisms of adaptation to ocean warming and acidification in a marine copepod, Proceedings of the National Academy of Sciences, 119(38): e2201521119. https://doi.org/10.1073/pnas.2201521119 Cheaib M., Amirabad A.D., Nordström K.J.V., Schulz M.H., and Simon M., 2015, Epigenetic regulation of serotype expression antagonizes transcriptome dynamics in Paramecium tetraurelia, DNA Research, 22(4): 293-305. https://doi.org/10.1093/dnares/dsv014 Chen L., Fu C.M., and Wang G.Y., 2016, Microbial diversity associated with Ascidians: a review of research methods and application, Symbiosis, 71: 19-26. https://doi.org/10.1007/s13199-016-0398-7 Chen Y., Gao Y., Huang X., Li S., and Zhan A., 2021, Local environment‐driven adaptive evolution in a marine invasive ascidian (Molgula manhattensis), Ecology and Evolution, 11: 4252-4266. https://doi.org/10.1002/ece3.7322 Chen Y.Y., Ni P., Fu R.Y., Murphy K.J., Wyeth R.C., Bishop C.D., Huang X.H., Li S.G., and Zhan A.D., 2022, (Epi)genomic adaptation driven by fine geographical scale environmental heterogeneity after recent biological invasions, Ecological Applications, 34(1): e2772. https://doi.org/10.1002/eap.2772 Deng Z.C., Liu H., He C.K., Shou C.Y., and Han Z.Q., 2021, Heat shock protein 70 (HSP70) and heat shock transcription factor (Hsf) gene families in Cynoglossus semilaevis: genome-wide identification and correlation analysis in response to low salinity stress, Marine and Freshwater Research, 72(8): 1132-1141. https://doi.org/10.1071/MF20326 Evans J.S., Erwin P.M., Shenkar N., and López‐Legentil S.L., 2017, Introduced Ascidians harbor highly diverse and host-specific symbiotic microbial assemblages, Scientific Reports, 7(1): 11033. https://doi.org/10.1038/s41598-017-11441-4
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