International Journal of Aquaculture, 2024, Vol.14, No.4, 184-194 http://www.aquapublisher.com/index.php/ija 187 suggest that epigenetic mechanisms could be at play in regulating these genes to meet the demands of an aquatic lifestyle (Yuan et al., 2021). Although specific studies on epigenetic modifications in aquatic life forms are limited, the existing evidence underscores their potential role in facilitating rapid and reversible adaptations to environmental changes. 3.3 Evolution of developmental pathways The evolution of developmental pathways is a key factor in the diversification of aquatic life forms. Developmental pathways are regulated by a complex interplay of transcription factors and gene regulatory networks. In plants, for example, the evolution from unicellular aquatic algae to complex flowering plants involved significant changes in transcription factors and their associated regulatory networks. These changes were driven by alterations in DNA binding specificity, protein-protein interactions, and cis-regulatory elements, which collectively contributed to the functional evolution of transcription factors (Romani and Moreno, 2020). Similarly, in marine mammals, the adaptation to aquatic environments required modifications in developmental pathways to support new physiological and morphological traits. The study of these evolutionary processes in both plants and animals provides valuable insights into the molecular mechanisms underlying the diversification of life forms in aquatic environments. 4 Environmental Factors Driving Molecular Diversification 4.1 Adaptation to different water conditions Adaptation to varying water conditions is a significant driver of molecular diversification in aquatic life forms. The transition between marine and freshwater environments, characterized by steep salinity gradients, poses a substantial osmotic challenge for many species. For instance, diatoms exhibit molecular acclimation mechanisms to cope with hypo-osmotic stress when transitioning from saline to freshwater environments, highlighting the role of cellular mechanisms in overcoming salinity barriers (Bilcke and Kamakura, 2023). Similarly, the genomic adaptations in marine mammals, such as changes in genes associated with thermoregulation and deep diving, underscore the importance of molecular changes in adapting to aquatic lifestyles. These adaptations are crucial for survival and diversification in different aquatic habitats. 4.2 Pressure of predation and competition Predation and competition are pivotal biotic factors influencing the diversification of aquatic species. In postglacial freshwater fish species, predation and competition have been implicated in the divergence into multiple ecomorphs within lakes, suggesting that these biotic pressures drive morphological and ecological diversification (Condamine et al., 2019; Tiddy et al., 2023). The unequal body shape diversification in the Gondwanan fish radiation (Characiformes) is influenced by competition for niches and habitat variation. Neotropical characiform lineages exhibit greater morphological diversity compared to their African counterparts, likely due to competition with cypriniform fishes in Africa and the availability of diverse habitats in the Neotropics (Burns et al., 2023). These examples illustrate how predation and competition pressures can lead to significant diversification in aquatic life forms. 4.3 Influence of climate change Climate change is a critical abiotic factor driving molecular diversification in aquatic ecosystems. Global cooling and warming have been shown to influence speciation rates in marine and freshwater clades differently. For example, speciation rates in marine clades of Anomura crustaceans are positively correlated with global cooling, while freshwater clades show increased speciation rates with global warming (Davis et al., 2016). Climate fluctuations have played a significant role in the diversification of true water bugs (Nepomorpha) during the Mesozoic, with palaeoecological opportunities promoting lineage diversification (Friedman et al., 2021). The interaction of multiple climate-change drivers, such as ocean warming, acidification, and deoxygenation, also affects aquatic productivity and species responses, highlighting the complex influence of climate change on molecular diversification (Häder and Gao, 2023). Understanding these dynamics is crucial for predicting and mitigating the impacts of ongoing climate change on aquatic biodiversity.
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