IJMS2025v15n2

International Journal of Marine Science, 2025, Vol.15, No.2, 92-106 http://www.aquapublisher.com/index.php/ijms 101 and gene exchange among populations. Vu et al. (2020) study on Australian black tiger shrimp, through more than 100,000 SNPs and several microsatellites, they consistently revealed the three major genetic groups along the coast, and there are a small number of significant microsatellite sites with F_<sub>ST</sub> under different environmental conditions (Vu et al., 2020). Such sites may be related to local adaptation (such as salinity, temperature selection). Mitochondrial DNA can also bind to molecular clocks for population history simulation. By comparing the divergence of mitochondrial haplotypes in each population, the population expansion time can be estimated. A study of pimples using control zone sequences to infer that it experienced a significant population expansion in the late Pleistocene, and then the distribution contracted due to the decline of sea level during the glacial period. Mitochondria can also be used to identify hidden species: If distinct mitochondrial branches are found in the same domain population and the differences exceed the species level, it is often suggested that there is an implicit new species that are not described. 6.2 Population differentiation index (Fst) and gene flow assessment The population differentiation index F<sub>ST</sub> is an important indicator to measure the degree of genetic differentiation among different geographical populations and is often used to evaluate the gene flow level of shrimp populations. The F<sub>ST</sub> value is 0 to 1. The higher the value, the greater the genetic difference between populations and the less gene communication. Many studies have revealed which geographical barriers significantly restrict gene flow by calculating the F<sub>ST</sub> of different regional populations of shrimp. For example, analyzing the wild populations along the coast of Australia's black tiger shrimp was obtained with an average F<sub>ST</sub> of about 0.05-0.10, indicating that there is a clear spatial genetic structure. The Chinese shrimp populations in the Bohai Sea and the Yellow Sea in China are often very low, meaning that seasonal currents make them closely connected. In addition, software that analyzes population structures (such as STRUCTURE) can be used to divide implicit groups through the F<sub>ST</sub> matrix. Many shrimp studies have found that the genetic structure of the population often coincides with the marine geographical area. For example, the Indo-Pacific black tiger shrimp can be divided into 7 genetic groups, corresponding to East Africa, Indo-Sri Lanka, Southeast Asia, northern Australia and other regions. The F<sub>ST</sub> values ​ ​ between these groups range from 0.05 to 0.25, reflecting different regional isolation. 6.3 Construction of haplotype network and historical diffusion model Haplotype network analysis is a method to visually display the evolutionary relationship of mitochondria or other haplotype sequences, which is quite useful in the historical inference of shrimp populations. By drawing haplotype networks of different geographical groups, the clustering, frequency and geographical distribution of haplotypes can be observed, thereby inferring historical population expansion, migration routes, etc. Aguirre-Pabón constructed a network of COI haplotypes of invasive platylensis shrimp in Colombia. The results showed that the two major lineages (Lineage I and II) differed by 7.7% from each other, each containing multiple shared haplotypes from Asian and African countries. This suggests that these invading groups are derived from repeated introductions from multiple regions, rather than from a single source. Similarly, a global analysis of mitochondrial haplotypes of wild and farmed shrimps in Pacific white shrimps found that the haplotypes in the American sample were relatively concentrated, while the Asian breeding population showed a pattern of dominance of several major haplotypes, suggesting that the Asian breeding population may have experienced bottlenecks (Yudhistira and Arisuryanti, 2019). In addition to qualitative observation, the historical diffusion process of shrimp can also be quantitatively reconstructed with the help of statistical diffusion models. Commonly used methods include discrete geographical diffusion models based on Bayesian analysis, where molecular clocks can be used to estimate the time and diffusion order of the occurrence of ancestral nodes in each region. For example, Frolová et al. (2022) used BEAST to perform spatiotemporal diffusion simulation of Pon-I taxa in the long-armed family. The results supported that the taxa spread from the IWP to the eastern Pacific Ocean about 55 million years ago, and then crossed the nascent Panama Isthmus into the Atlantic Ocean. This model provides us with a timeline for the macroscopic diffusion of species. Similar methods can also be used for recent human-proliferation events.

RkJQdWJsaXNoZXIy MjQ4ODYzNA==