International Journal of Aquaculture, 2024, Vol.14, No.4, 184-194 http://www.aquapublisher.com/index.php/ija 185 integrating the results of multiple studies, this research aims to provide a comprehensive understanding of how molecular mechanisms promote the diversification of aquatic life forms, thereby offering valuable insights for evolutionary biology and conservation science.. 2 Genetic Basis of Diversification 2.1 Role of gene duplication Gene duplication is a fundamental mechanism that contributes to the diversification of aquatic life forms by providing raw genetic material for evolutionary innovation. For instance, the genome of the water strider Gerris buenoi reveals numerous local gene duplications and expansions of gene families that are crucial for adaptations to a water surface lifestyle. These duplications affect processes such as growth, vision, desiccation resistance, detoxification, olfaction, and epigenetic regulation, which are essential for the water strider's survival and diversification in aquatic environments (Armisén et al., 2018). Similarly, the duplication of the Na+/K+-ATPase gene in clitellate annelids is associated with their transition from marine to freshwater habitats, suggesting that these duplications played a significant role in their diversification (Horn et al., 2019). The dynamic evolution of gene families, including gene duplication and deletion, has been shown to drive phenotypic diversity and adaptation in various aquatic species, such as African cichlid fishes and Hawaiian drosophilids (Harris and Hofmann, 2015). 2.2 Horizontal gene transfer Horizontal gene transfer (HGT) is another critical mechanism that accelerates microbial evolution and promotes diversification and adaptation in aquatic environments. In marine ecosystems, the cyanobacterium Prochlorococcus exhibits a highly streamlined genome with frequent gene exchange, facilitated by mobile genetic elements known as tycheposons. These elements drive genomic plasticity and niche differentiation by carrying genes important for nutrient acquisition and other adaptive traits. The efficient dispersal and transmission of tycheposons through extracellular vesicles and phage particles highlight the significant role of HGT in the diversification of marine microbes (Hackl et al., 2020). Furthermore, the formation of new ecologically distinct populations (ecotypes) in the Microcystis aeruginosa complex is driven by mutations in key functional genes and the acquisition of new metabolic pathways through HGT, allowing these populations to exploit new resources and coexist with parental populations (Escalera et al., 2021). 2.3 Mutations and genetic variability Mutations and genetic variability are essential for the adaptive diversification of aquatic organisms. In the rotifer Brachionus calyciflorus, genetic variation and differences in gene expression related to temperature tolerance play a significant role in local adaptation and ecological diversification. The identification of candidate genes associated with metabolism and stress response highlights the importance of genetic variability in adapting to different thermal environments (Paraskevopoulou et al., 2019). The adaptation of fishes to changing salinity involves genetic changes in osmoregulatory systems, with natural selection targeting genes coding for key cellular ion exchange enzymes such as V-type, Ca2+, and Na+/K+-ATPases. These genetic changes support the transition across salinity boundaries and contribute to the diversification of fish species (Velotta et al., 2022). The study of diatoms also reveals that habitat transitions, such as from marine to freshwater environments, are influenced by genetic variability and adaptive mutations, which play a crucial role in their diversification (Roberts et al., 2023). 3 Regulatory Networks and Evolution 3.1 Gene regulatory networks Gene regulatory networks (GRNs) play a crucial role in the diversification of aquatic life forms by orchestrating the expression of genes in response to environmental changes. In marine mammals, for instance, the adaptation to aquatic environments involved significant modifications in GRNs. Comparative genomics has revealed that genes associated with thermoregulation, such as NFIA and SEMA3E, have undergone convergent evolution to facilitate the transition from land to water. These genes are involved in the formation of blubber and vascular development, respectively, which are essential for maintaining body temperature in aquatic environments (Figure 1) (Triant et
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