International Journal of Aquaculture, 2024, Vol.14, No.3, 139-153 http://www.aquapublisher.com/index.php/ija 141 particularly important in environments that experience frequent and unpredictable changes, such as fluctuating water levels, temperature shifts, and variations in nutrient availability. For example, the plastic responses of amphibious fishes to terrestrial and aquatic environments not only facilitate their survival but also provide insights into the evolutionary processes that may have enabled the transition of vertebrates from water to land (Wright and Turko, 2016). In aquatic plants, phenotypic plasticity in traits such as growth form, root length, and branching patterns allows them to exploit different ecological niches and compete effectively with other species (Szabó et al., 2018). Moreover, phenotypic plasticity can buffer populations against environmental stressors, potentially providing a temporary adaptive advantage while genetic adaptation catches up. This buffering effect is crucial in the context of global environmental changes, such as climate change, which impose new selection pressures on aquatic ecosystems (Gibbin et al., 2017). The ability to rapidly adjust phenotypes in response to these changes can enhance the resilience of populations and ecosystems, promoting stability and persistence in the face of environmental perturbations. 3 Genetic Evolution 3.1 Definition and processes Genetic evolution is a fundamental process that drives the adaptation of species to their environments through changes in their genetic makeup over generations. This section will discuss the definition and processes of genetic evolution, the roles of natural selection and genetic drift, and the significance of genetic evolution in long-term adaptation. Genetic evolution refers to changes in the frequency of alleles (different versions of a gene) within a population over time. These changes result from various processes including mutation, gene flow, genetic drift, and natural selection. Mutations are random changes in the DNA sequence that can introduce new genetic variations. Gene flow occurs when individuals migrate between populations, bringing new alleles into a population. Genetic drift is the random fluctuation of allele frequencies from one generation to the next, which can have significant effects in small populations. Natural selection is the process by which certain traits become more common in a population because they confer a survival or reproductive advantage (Foote et al., 2015). The combination of these processes leads to genetic diversity within populations, which is crucial for adaptation to changing environments. For instance, in the aquatic firefly, genetic adaptations to freshwater environments involve significant changes in genes related to metabolic efficiency and hypoxia response (Zhang et al., 2020). 3.2 Natural selection and genetic drift Natural selection and genetic drift are two primary mechanisms that drive genetic evolution. Natural selection acts on phenotypic variation, favoring traits that enhance an organism’s fitness in its environment. For example, marine mammals such as whales and dolphins have evolved specific adaptations for thermoregulation and deep diving, driven by positive selection on genes involved in these traits (Yuan et al., 2021). Genetic drift, on the other hand, refers to random changes in allele frequencies that can lead to significant genetic differences between populations, particularly in small or isolated populations. This stochastic process can result in the loss of genetic variation and the fixation of alleles. In freshwater snails, genetic drift has been shown to influence the evolution of phenotypic plasticity, with high rates of gene flow necessary to maintain genetic diversity (Hollander et al., 2017). 3.3 Role in long-term adaptation Genetic evolution plays a critical role in the long-term adaptation of species to their environments. Over extended periods, genetic changes accumulate, leading to the emergence of new species and the development of complex adaptations. The study of aquatic vertebrates, for instance, reveals how genomic changes have facilitated their adaptation to aquatic life. For example, the genomes of marine mammals exhibit convergent evolution, with
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