International Journal of Marine Science, 2025, Vol.15, No.4, 186-198 http://www.aquapublisher.com/index.php/ijms 188 2.3 Brief description of the relationship between population characteristics and evolution Due to geographical isolation and environmental differences, there may be differences in phenotypic characteristics and genetic composition of mackerel populations distributed in different sea areas. Through morphological research in the early days, some scholars divided Japanese mackerels along the coast of China into Yellow and Bohai Sea populations and East China Sea populations based on metrology characteristics, suggesting that the groups in these two major sea areas may be independent of each other. However, mitochondrial DNA sequence analysis did not detect significant genetic differentiation between the Yellow Sea and East China Sea populations, showing high genetic similarity (Zhu et al., 2016). This suggests that traditional morphological classifications may be affected by environmental shaping, and genetic markers can provide independent evidence. It is generally believed that Japanese mackerels along the coast of China may have genetic differentiation in the Yellow and Bohai Seas and the East China Sea, but the degree is relatively low. In the Indian Ocean region, studies have found that narrowband mackerels may have east-west differentiation across the "Wallace Line": East Indian populations are genetically different from Western Australian populations, similar to the pattern of differentiation of other Indo-Pacific marine organisms on both sides of this biogeographical boundary. The mackerel population along the Atlantic Ocean is completely different from the Indo-Pacific species because it is separated from the North and South American continents. But inside the Atlantic Ocean, populations in different regions are closely linked. Taking the Sierra mackerel on the coast of Brazil as an example, the populations from Kumana, Venezuela to the southern end of Brazil have low genetic diversity and frequent sharing of haplotypes, indicating that it is a single genetic library. This result suggests that the Sierra mackerel population on the western Atlantic Ocean is integrated and has no significant differentiation (Santa Brígida et al., 2007; Cunha et al., 2020). Figure 1 Digital X-ray images of Scomberomorus species (A-J) from the Northern Indian Ocean revealing the diversity, fork length (FL), and number of vertebrae (Adopted from Jeena et al., 2022) 3 Research Progress on Genetic Diversity and Population Structure 3.1 Early study of mitochondrial DNA and microsatellite markers Molecular research on the genetic structure of mackerel populations began in the late 20th and early 21st century. Mitochondrial DNA (mtDNA) is widely used in fish population geography research due to its single parental
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