International Journal of Molecular Zoology 2024, Vol.14, No.2, 84-96 http://animalscipublisher.com/index.php/ijmz 85 genomic signatures of adaptation in reptiles inhabiting extreme environments? How do these genomic adaptations correlate with physiological and morphological traits? What are the evolutionary processes driving these adaptations, and how do they contribute to speciation? By addressing these questions, this study seeks to provide a comprehensive understanding of the mechanisms underlying reptilian adaptation to extreme environments, contributing to the broader field of evolutionary biology and offering valuable insights for conservation efforts. 2 Genomic Basis of Thermoregulation 2.1 Genetic mechanisms of heat tolerance The genetic mechanisms underlying heat tolerance in reptiles have been extensively studied, revealing significant insights into how these organisms adapt to high-temperature environments. For instance, research on three sympatric species of Cuban Anolis lizards (Anolis allogus, A. homolechis, and A. sagrei) identified differentially expressed genes (DEGs) that are crucial for heat adaptation. In particular, the warm-adapted A. homolechis showed upregulation of ribosomal protein genes, suggesting that enhanced protein synthesis is a key physiological mechanism for coping with higher temperatures (Akashi et al., 2016). Additionally, a study on the Sceloporus undulatus complex demonstrated that effective thermoregulation can limit local adaptation of thermal tolerance, indicating that behavioral plasticity might hinder the evolutionary shift towards greater heat tolerance (Buckley et al., 2015). Furthermore, the evolutionary potential of heat tolerance in Drosophila subobscura was found to be influenced by the methodology used in thermal tolerance assays, with static assays providing higher heritability estimates than slow ramping assays (Castañeda et al., 2019). 2.2 Genomic adaptations to cold environments Reptiles inhabiting cold environments have developed various genomic adaptations to survive low temperatures. For example, terrestrially hibernating reptiles like the hatchling painted turtles (Chrysemys picta marginata) exhibit freeze tolerance, which involves the upregulation of genes encoding proteins for iron binding, antioxidant defense, and serine protease inhibitors. These adaptations help counteract the effects of ischemia caused by plasma freezing (Storey, 2006). Similarly, a study on the tuatara (Sphenodon punctatus) demonstrated that these cold-adapted reptiles can modify their thermoregulatory behavior in response to different thermal environments, maintaining higher body temperatures even in low-quality habitats (Besson and Cree, 2010). Moreover, research on the invasive brown anole (Anolis sagrei) revealed that limited recombination in certain genomic regions might constrain the adaptation to colder climates, highlighting the role of genetic constraints in evolutionary stasis (Bock et al., 2023). 2.3 Evolutionary significance of thermoregulatory genes The evolutionary significance of thermoregulatory genes is evident from their recurrent involvement in adaptation to various thermal environments. A comparative genomics study on lacertid lizards and other vertebrates identified a set of 200 genes with signatures of positive diversifying selection, many of which are involved in physiological and morphological adaptations to climate. These genes form a tightly connected interactome, enriched in functions related to climate adaptation and organismal stress response, indicating a high degree of functional similarity and posttranslational modifications across different species (Figure 1) (Valero et al., 2019; Valero et al., 2021). Additionally, the study on tropical Anolis lizards showed that cold tolerance evolves faster than heat tolerance due to the differential exposure to selection pressures, emphasizing the role of thermoregulatory genes in shaping evolutionary trajectories (Muñoz et al., 2014). The identification of candidate genes involved in high elevation adaptation in Phrynocephalus lizards further underscores the importance of coordinated changes in multiple genes for thermoregulation and overall fitness in extreme environments (Yang et al., 2014).
RkJQdWJsaXNoZXIy MjQ4ODYzNA==