International Journal of Marine Science, 2025, Vol.15, No.4, 179-185 http://www.aquapublisher.com/index.php/ijms 183 7.2 Genetic pathways related to stress adaptation The genes of the two oysters also differ in the part that controls the response to salinity changes. Pacific oysters can activate some specific metabolic pathways under high salinity conditions, while Hong Kong oysters show similar coping mechanisms under low salinity conditions (Zhang et al., 2022). This shows that their genetic systems have formed ways to adapt to various environments, which is the result of long-term natural selection. Using the Pacific oyster (Crassostrea gigas) as a model, the core stress and immune pathways activated under various stress conditions-including high temperature, heavy metals, low salinity, and pathogen exposure—are illustrated (Figure 2) (Zhang et al., 2016). Gene families marked with bold black borders in the figure, such as HSPs, SODs, and IAPs, represent expanded genes that are significantly upregulated under multiple stress scenarios. This capacity to respond to diverse stressors is a clear sign of the evolutionary enhancement of the oyster’s innate immune system. When exposed to salinity stress, each species activates a different set of genes. These differences in gene expression show that they rely on distinct biological responses to adapt. Their genetic patterns line up with their home environments, pointing to the strong influence of local adaptation on their evolution. Figure 2 The major stress-responsive pathway-related genes inCrassostrea gigas (Adopted from Zhang et al., 2016) Image caption: Protein folding systems included HSPs and HSF in the heat shock response and GRP78, GRP94, PERK, CRT, CNX, eIF2α, and Ire1 in the endoplasmic reticulum unfolded-protein response (UPR ER). Apoptotic pathways included IAPs, BAG, Bcl2 like, caspases, BI-1, TNFR, and FADD. The xenobiotic biotransformation and antioxidant systems included CYP450, MO, SOD, Gpx, Prx, and CAT. Boxes with bold black borders indicate oyster expanded gene families, including HSPs, IAPs, and SODs, and the filled colors represent the degree of upregulation in RPKMtreatment/RPKMcontrol by stress, using transcriptomes from oysters challenged with nine different types of stressors (Adopted from Zhang et al., 2016) 8 Implications for Conservation and Aquaculture 8.1 Breeding applications of genetic markers With more is known about stress tolerance genes, especially those linked to temperature and salinity, practical applications are emerging. Molecular markers-such as adaptive SNPs-are now being used to select oyster strains better suited for particular environments. It’s not just theory anymore. High-throughput genotyping has made these tools available on a broader scale. That said, selective breeding isn't a one-size-fits-all solution. The usefulness of certain markers can vary by location and environmental condition, so there’s still a need for local adaptation strategies.
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