International Journal of Molecular Zoology 2024, Vol.14, No.2, 111-127 http://animalscipublisher.com/index.php/ijmz 115 4.2 Epigenetic modifications and phenotypic plasticity Epigenetic modifications also play a critical role in the regulation of migratory behaviors. These modifications can influence gene expression without altering the underlying DNA sequence, thereby contributing to phenotypic plasticity. For example, Sharma et al. (2018) explored the physiological and gene expression changes in the red-headed bunting (Emberiza bruniceps) during spring and autumn migrations. The study hypothesized that birds employ different molecular strategies during spring and autumn migrations to meet varying environmental demands. By simulating photoperiods, the researchers investigated the changes in behavior, physiology, and gene expression in birds under migratory and non-migratory states. The study found that birds migrating in spring exhibited higher body fat and weight, as well as more intense migratory restlessness (Zugunruhe), compared to those migrating in autumn, which had lower body fat and weight. Additionally, the study revealed significant changes in the expression of epigenetic genes (such as dnmt3a and tet2) during migratory states, suggesting that epigenetics play a crucial role in seasonal migration. These findings provide an important molecular basis for understanding the adaptive mechanisms of migratory birds. In the study of physiological and molecular changes in Emberiza bruniceps during spring migration, Sharma et al. (2021; 2022) focused on the changes in gene expression and protein levels related to fatty acid synthesis and transport in the liver and flight muscles. The research found that genes associated with fatty acid synthesis (acc, dgat2) and transport (cd36, fabp3, cpt1) were upregulated in the migratory state. Furthermore, increased expression of genes related to calcium signaling, cellular stress, and metabolic pathways was observed in the mediobasal hypothalamus, indicating that energy utilization during migration is epigenetically regulated. 4.3 Inheritance of migratory behaviors The genetics of migratory behavior is a complex process involving genetic and epigenetic factors. In blackpoll warblers (Setophaga striata), it has been found that variations in the lengths of candidate genes such as Clock and Adcyap1 are significantly correlated with migratory traits such as timing and duration. The maximum allele length of the Clock gene is significantly negatively correlated with spring arrival dates, while the minimum allele length of the Adcyap1 gene is significantly associated with spring departure dates and fall arrival dates (Ralston et al., 2019). Additionally, the study found an interaction effect between the lengths of the Clock and Adcyap1 genes on the duration of migration. These results indicate that specific genetic variations can be inherited and influence migratory behavior across generations. Additionally, the study on European blackcaps demonstrated that the propensity to migrate, as well as the orientation and distance of migration, mapped to specific genomic regions, indicating a heritable component to these traits (Delmore et al., 2020). The retention of chromosomal inversions in rainbow trout (Oncorhynchus mykiss) also highlights the role of genetic inheritance in maintaining migratory behaviors within populations (Arostegui et al., 2019). The genetic and epigenetic regulation of migration involves a complex interplay of multiple genes and epigenetic modifications that contribute to the phenotypic plasticity and inheritance of migratory behaviors in animals. Understanding these mechanisms is crucial for elucidating how migratory species adapt to changing environments and for the conservation of migratory populations. 5 Physiological Adaptations to Migration 5.1 Energy metabolism and fat storage Migratory animals exhibit a range of physiological adaptations that enable them to undertake long-distance journeys. These adaptations are crucial for optimizing energy use, enhancing endurance, and regulating the physiological changes necessary for migration. Energy metabolism and fat storage are critical for migratory animals, as these processes provide the necessary fuel for long-distance travel. Migratory birds, for instance, accumulate substantial fat reserves, which can constitute up to 50%-60% of their body mass. These fat stores are then oxidized at high rates to sustain prolonged flight (Guglielmo, 2018). The ability to store and utilize fat efficiently is supported by high capacities for fatty acid uptake, cytosolic transport, and oxidation in the flight muscles. Additionally, changes in energy intake, digestive capacity, and liver lipid metabolism contribute to migratory fattening.
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