Genetic Diversity and Environmental Adaptation Signatures of the Great Seahorse (Hippocampus kelloggi) in the Coastal Regions of the Indo-Pacific as Revealed by Whole-Genome Re-Sequencing

The great seahorse (<i>Hippocampus kelloggi</i>) is one of the larger species within the seahorse group and is widely distributed in coastal areas of the Indo-Pacific. However, the natural resources of this species continue to decrease, rendering it a vulnerable species that faces a high risk of extinction. Therefore, there is an urgent need to conduct research on the genetic diversity of this species to protect its genetic resources. In this study, we conducted whole-genome re-sequencing (WGRS) on three <i>H. kelloggi</i> populations from the Red Sea (RS, n = 30), the Andaman Sea (AS, n = 13), and the South China Sea (SCS, n = 13), and a total of 1,398,936 high-quality single-nucleotide polymorphisms (SNPs) were identified. The results indicate that the average observed heterozygosity (<i>Ho</i>) and the average expected heterozygosity (<i>He</i>) for the RS, AS, and SCS populations are 0.2031 and 0.1987, 0.1914 and 0.1822, and 0.2083 and 0.2001, respectively. The three geographic populations exhibit a high degree of genetic differentiation with only a minimal gene flow between them. Consistently, in a population structure analysis, the three groups are also clearly distinguished, which is consistent with the results of the population differentiation coefficient. Demographic analyses revealed that the effective population size (<i>Ne</i>) of the SCS population underwent a dramatic bottleneck during the Last Glacial Maximum (LGM), followed by a substantial recovery, whereas the RS and AS populations maintained stable <i>Ne</i> values throughout this period. To investigate adaptive responses to climate change in the SCS population, we employed selective elimination analysis, which identified 21 candidate genes potentially involved in environmental adaptation. Of particular significance were <i>myo5a</i>, <i>hps4</i>, <i>znf385a</i>, <i>msh3</i>, and <i>pfkfb4</i>, which likely play crucial roles in the adaptive mechanisms of <i>H. kelloggi</i>. This comprehensive study not only illuminates the genetic diversity patterns of <i>H. kelloggi</i> but also provides a valuable foundation for future investigations into the species' evolutionary adaptations.