Bioscience Methods 2025, Vol.16, No.3, 137-153 http://bioscipublisher.com/index.php/bm 147 6 Case Studies: Regional Population Phylogeny and Identification 6.1 Comparative analysis of abalone from Southeastern China The southeastern coast of China (including the coasts of Fujian and Guangdong) is a world-famous abalone farming and distribution area, mainly including the local abalone (commonly known as "nine-hole abalone") and the introduced abalone. Molecular comparative studies of abalone resources in this area help to understand the genetic structure of different species and populations. First, the genetic diversity level of each cultured population of local abalone is generally high, but there is a slight differentiation between different farms. Through mitochondrial COI and control area analysis, it was found that several cultured abalone populations in the coastal area of Fujian shared most haplotypes, showing a close relationship, but there were also some population-specific haplotypes, which may be due to different seed sources. In general, abalone can basically be regarded as a large genetic exchange group in the southeastern coast, and no obvious regional differentiation has yet appeared. In contrast, the genetic diversity of the introduced abalone population is slightly lower than that of local abalone due to its short farming history. The average nucleotide diversity of mitochondrial haplotypes of the wrinkled abalone population in some farms in Fujian is about 0.002,0, which is lower than 0.003,5 of the variegated abalone population in the same period. This may be caused by the introduction bottleneck and artificial breeding. However, from the perspective of molecular pedigree, most of these wrinkled abalone populations are mixed with the original populations in Japan or the north on the same lineage. For example, a study comparing the wrinkled abalone cultured in Fujian with the original population in Shandong pointed out that the COI sequences of the two had only 0-1 base differences and no differentiated branches were formed (Ren et al., 2017). This shows that the wrinkled abalone in the southeast coast basically continues the genetic background of the introduced original species and has not yet significantly differentiated from local abalone or other introduced batches. On the other hand, in natural sea areas, there are still sporadic wild variegated abalone populations in the southeast coast (mainly in Taiwan Shoals and other places). Studies have found that there is no systematic difference in mitochondrial DNA between wild variegated abalone and farmed populations, but nuclear gene markers such as microsatellites show that unique alleles appear in wild populations. This suggests that when protecting local wild resources, its uniqueness should be considered to avoid genetic confusion of escaped individuals from aquaculture. Based on these molecular evidences, it can be seen that although the abalone species (Haliotis diversicolor and Haliotis discus hannai) in the southeastern coast of China exist in the same area, they are clearly genetically bounded and not mixed: the Haliotis diversicolor populations are clustered together, while the Haliotis discus hannai are classified as another group with the northern population. The COI sequence difference between the two is more than 20 bases, which can be accurately distinguished (Figure 2) (Bachry et al., 2019). Figure 2 (a) Shell of H. diversicolor squamataand (b) shell of H. diversicolor (Adopted from Bachry et al., 2019)
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