International Journal of Molecular Ecology and Conservation 2024, Vol.14, No.5, 208-217 http://ecoevopublisher.com/index.php/ijmec 211 in gene expression (Cheng et al., 2019). These insights highlight the potential of epigenetic mechanisms to contribute to the resilience of crustacean species facing climate change. 3.3 Evolutionary selection and genomic signatures of adaptation Evolutionary selection leaves distinct genomic signatures that can be used to identify adaptive traits in crustaceans. In the invasive green crab Carcinus maenas, a cluster of single nucleotide polymorphisms (SNPs) associated with temperature adaptation was identified as a potential genomic island of divergence. This cluster showed a significant enrichment of coding substitutions, suggesting that it plays a critical role in the crab's ability to adapt to varying thermal conditions (Tepolt and Palumbi, 2020). Such genomic signatures provide valuable insights into the specific genetic changes that underlie adaptation to environmental stressors. Similarly, in the world ocean krill, comparative genomics has uncovered candidate genes with signatures of adaptive evolution, particularly in species endemic to cold environments like the Antarctic krill Euphausia superba. These genes are involved in thermal reception and other cold-adaptation processes, indicating parallel genetic responses to similar selection pressures across Antarctic taxa (Choquet et al., 2023). These findings demonstrate how evolutionary selection can shape the genomic landscape of crustaceans, enabling them to survive and thrive in changing climates. 3.4 Gene Expression Responses to Environmental Stressors Gene expression responses are a key component of crustacean adaptation to environmental stressors, allowing organisms to modulate their physiological processes in response to changing conditions. In the deep-sea squat lobster Shinkaia crosnieri, transcriptomic analyses revealed a large number of differentially expressed genes between populations from hydrothermal vents and cold seeps. These genes, particularly those associated with stress response and immunity, were up-regulated in hydrothermal vent populations, suggesting an enhanced capability to manage environmental stresses (Cheng et al., 2019). In the estuarine oyster Crassostrea ariakensis, genes exhibiting high plasticity showed strong selection in regulatory regions, indicating that gene expression modulation is a critical adaptive strategy. This plasticity allows for rapid adjustments to environmental changes, such as fluctuations in temperature and salinity, which are common in estuarine environments (Li et al., 2021). These examples illustrate the importance of gene expression changes in facilitating crustacean adaptation to diverse and dynamic environmental conditions, highlighting the complex interplay between genetic and environmental factors in shaping adaptive responses. 4 Key Genomic Pathways Involved in Environmental Adaptation 4.1 Heat shock proteins and thermal tolerance Heat shock proteins (HSPs) play a crucial role in the thermal tolerance of crustaceans, acting as molecular chaperones that help maintain protein stability under stress conditions. In the tidepool copepod Tigriopus californicus, local adaptation to temperature is evident, with significant genetic variation in thermal tolerance observed across different populations. This suggests that HSPs may be involved in the limited potential for adaptation to increasing temperatures, as heat-tolerant phenotypes in low-latitude populations cannot be achieved in high-latitude populations through acclimation or selection (Kelly et al., 2012). Similarly, in the invasive green crab Carcinus maenas, rapid adaptation to temperature changes is facilitated by genomic islands of divergence, which may include genes related to HSPs, contributing to the species' thermal physiology and invasive success (Tepolt and Palumbi, 2020). The role of HSPs in thermal tolerance is further supported by studies on Antarctic krill, where genetic variation and adaptive protein evolution are linked to cold adaptation. Genes governing thermal reception, such as TrpA1, have been identified as candidates for cold adaptation, indicating that HSPs and related pathways are crucial for survival in extreme temperatures (Choquet et al., 2023). These findings highlight the importance of HSPs in enabling crustaceans to cope with thermal stress, although the extent of their adaptive potential may vary among species and populations.
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