International Journal of Marine Science, 2025, Vol.15, No.1, 1-14 http://www.aquapublisher.com/index.php/ijms 9 that the African abalone genome lacks the mitochondrial antiviral signaling protein MAVS, which is consistent in all abalone. However, African abalone may make up for this defect by evolving different RIG-I-like receptor pathways to cope with viral diseases that are more prone to outbreaks under higher water temperature conditions. Some phagocytosis and inflammatory response-related genes (such as NOD-like receptors and inflammasome components) of African abalone carry unique alleles, which are speculated to be related to their disease resistance spectrum. This study conducted a gene family expansion analysis on African abalone and found that gene families related to energy metabolism and environmental information processing are particularly abundant in its genome. For example, African abalone has extra copies of photopigment genes and circadian rhythm genes, which may help it perceive and adapt to diurnal changes and light conditions in coastal shallow water environments. These characteristics have improved the adaptability of African abalone to conditions such as high temperature during the day and low oxygen at night. Through the above analysis, this study preliminarily outlined the genetic basis of African abalone's heat-resistant adaptation, that is, to resist high temperature stress by strengthening heat shock response, antioxidant and metabolic regulation. This information is of reference value for the future breeding of high-temperature tolerant abalone varieties. For example, molecular marker-assisted selection can be carried out for key genes such as HSP70, thereby genetically improving the heat tolerance of farmed abalone. 5.3 Haliotis laevigata: Local selection signals in shell morphology and stress response The Australian green abalone is a large abalone species unique to Australia, known for its beautiful green shell and large size. Green abalone often inhabits environments with turbulent water and moderate temperatures, and has certain stress resistance and unique shell shape. This study used population genomics methods to detect local selection signals related to shell morphology and stress resistance in the green abalone genome. This study compared the frequency distribution of green abalone genes in different geographical populations and found that several gene regions had undergone significant differentiation under the action of selection pressure. For example, in the QTL region that controls shell shape and thickness, this study detected significant differentiation signals. These regions contain genes that regulate mantle development, such as bone morphogenetic protein BMP pathway genes and shell matrix protein genes (Sandoval-Castillo et al., 2018). It is speculated that in an environment with high waves and fast currents, individuals with flatter and thicker shells have a higher survival rate, so the favorable variants of these genes are positively selected and enriched in the population. Similarly, local selection related to stress resistance was also found. Green abalone may experience combined stress of high temperature and hypoxia in summer. This study found a selection region related to hypoxia tolerance on its chromosome 12, which is rich in heme-binding proteins and mitochondrial respiration regulatory genes. Individuals carrying specific mutations may be better able to tolerate temporary hypoxia in the intertidal zone, and these mutations therefore increase in frequency in wild populations. It is worth noting that this study compared the genomic differences between green abalone and its closely related species, black-lipped abalone (H. rubra), and found that some trait QTL regions in the hybrid offspring of the two showed hybrid vigor signals. For example, a gene region that affects growth rate is a single allele in green abalone and different in black abalone, but the hybrid offspring has better growth performance when they have both alleles (Figure 2) (Kube et al., 2023). This suggests that by hybridizing green abalone with other species, favorable mutations of different species can be combined to explore hybrid vigor. This has also been practiced in Australian abalone farming (green abalone × black abalone hybridization is used to cultivate fast-growing hybrid abalone). Local genomic selection studies of Australian abalone have revealed key regions that affect shell morphology and stress resistance. The genes in these regions can be used as targets for molecular breeding to improve the shell color, shell shape and environmental adaptability of farmed abalone. For example, through molecular marker selection, abalone populations can be made to have thicker shells and more resistant to pressure and heat, thereby improving aquaculture output and risk resistance. Case studies of Australian abalone have shown that analyzing local adaptation from a genome-wide perspective has important implications for the targeted breeding of economic traits.
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