International Journal of Molecular Zoology 2024, Vol.14, No.2, 84-96 http://animalscipublisher.com/index.php/ijmz 90 5 Adaptations to Marine Environments 5.1 Genomic adaptations to saltwater tolerance Marine reptiles have developed various genomic adaptations to tolerate high salinity environments. Studies on different species have identified key genes and genomic regions that play crucial roles in osmoregulation and ion transport. For instance, research on nine-spined sticklebacks (Pungitius pungitius) has highlighted the importance of genes such as growth hormone receptor 2 and DEAD box polypeptide 56 in adapting to different salinity levels (Shikano et al., 2010). Similarly, the Atlantic cod (Gadus morhua) has shown genomic divergence in regions associated with osmoregulation, which are crucial for survival in varying salinity conditions (Berg et al., 2015). In threespine sticklebacks (Gasterosteus aculeatus), specific quantitative trait loci (QTL) and candidate genes have been identified that contribute to salinity tolerance through mechanisms like ATP synthesis and hormonal signaling (Kusakabe et al., 2017). Additionally, the Alewife (Alosa pseudoharengus) has demonstrated parallel evolution in the expression of osmoregulatory genes, particularly those regulating gill ion exchange, which facilitates adaptation to freshwater and saltwater environments (Velotta et al., 2017). 5.2 Evolution of diving capabilities The evolution of diving capabilities in marine reptiles involves significant genomic changes that enhance their ability to withstand prolonged periods underwater. In cetaceans, for example, the loss of certain genes has been linked to improved diving adaptations. Genes such as F12 and KLKB1, which are associated with thrombus formation, and MAP3K19, related to oxidative stress-induced lung inflammation, were inactivated in ancestral cetaceans, reducing the risks associated with deep diving (Huelsmann et al., 2019). Additionally, genes involved in vasoconstriction and pulmonary surfactant composition, such as SLC6A18 and SEC14L3, respectively, have also been lost, further supporting diving adaptations (Huelsmann et al., 2019). These genomic changes highlight the complex evolutionary processes that enable marine reptiles to thrive in aquatic environments. 5.3 Genetic basis of osmoregulation Osmoregulation is a critical function for marine reptiles, allowing them to maintain ionic balance in varying salinity conditions. Decapod crustaceans, for example, have been studied extensively to understand the genetic mechanisms underlying osmoregulation. Research has identified 32 candidate genes involved in processes such as ion transportation, active ion exchange, and regulation of cell volume, which are essential for osmoregulation (Rahi et al., 2018). In Atlantic salmon (Salmo salar), genetic variation in osmoregulatory genes has been observed between landlocked and anadromous populations, indicating adaptive responses to freshwater environments (Yuan et al., 2021; Harder and Christie, 2022). These findings underscore the importance of specific genes and genomic regions in facilitating osmoregulation and adaptation to different osmotic niches in marine reptiles. 6 Case Study: Desert-Dwelling Reptiles 6.1 Genomic insights from the Gila monster The Gila monster (Heloderma suspectum) is a venomous lizard native to the southwestern United States and northwestern Mexico. Its adaptation to desert environments has been a subject of interest due to its unique physiological and genomic traits. Studies have shown that the Gila monster's genome contains specific adaptations that allow it to thrive in arid conditions, such as genes related to water retention and temperature regulation. These adaptations are crucial for survival in extreme environments where water is scarce and temperatures can be extreme (Araya-Donoso et al., 2021; Koochekian et al., 2022). 6.2 Comparative genomics of desert snakes Desert snakes, such as the sidewinder (Crotalus cerastes) and the horned viper (Cerastes cerastes), exhibit remarkable adaptations to their harsh environments. Comparative genomic studies have revealed that these snakes have evolved specific genetic traits that enhance their ability to conserve water and regulate body temperature. For instance, genes involved in kidney function and skin permeability have undergone positive selection, allowing these snakes to minimize water loss and survive in arid conditions. Additionally, the evolution of venom composition in these snakes is linked to their adaptation to desert prey, which often includes small mammals and other reptiles (Yang et al., 2014; Tollis et al., 2018; Valero et al., 2021).
RkJQdWJsaXNoZXIy MjQ4ODYzNA==