International Journal of Molecular Evolution and Biodiversity 2024, Vol.14, No.4, 197-207 http://ecoevopublisher.com/index.php/ijmeb 198 and gene expression changes on adaptation, and highlight the constraints and limitations of genetic adaptation in the face of rapid environmental changes. By achieving these objectives, This study expects to provide a comprehensive understanding of how avian species adapt genetically to rapidly changing environments, which will be crucial for predicting future adaptive responses and informing conservation strategies to mitigate the impacts of environmental changes on bird populations. 2 Mechanisms of Genetic Adaptation in Avian Species 2.1 Natural selection and its role in avian genetic adaptation Natural selection is a fundamental mechanism driving genetic adaptation in avian species. It operates by favoring individuals with advantageous traits that enhance survival and reproductive success in specific environments. For instance, studies on house finches (Haemorhous mexicanus) have shown that natural selection can lead to adaptive evolution by influencing genes related to fat metabolism, neurodevelopment, and ion binding, which are crucial for coping with environmental stresses (Backström et al., 2013). Additionally, research on songbirds has demonstrated that preexisting genetic variations play a predominant role in local adaptation, suggesting that natural selection acts on these standing genetic variants to facilitate rapid adaptation to new environmental conditions (Lai et al., 2019). 2.2 Genetic mutations and their impact on avian populations Genetic mutations introduce new genetic variations into populations, which can be acted upon by natural selection. These mutations can lead to significant evolutionary changes if they confer a survival advantage. For example, the spleen transcriptome analysis of house finches revealed a higher ratio of nonsynonymous to synonymous substitutions, indicating that genetic mutations contribute to adaptive evolution in passerine birds (Backström et al., 2013). Moreover, the study on nocturnal adaptation in birds highlights how genetic changes support adaptation to dim-light environments, showcasing the role of mutations in facilitating ecological niche shifts (Duc and Schöneberg, 2016). 2.3 Gene flow and genetic drift in avian species Gene flow and genetic drift are additional mechanisms influencing genetic adaptation in avian species. Gene flow, the transfer of genetic material between populations, can introduce new genetic variations that enhance adaptability. Conversely, genetic drift, the random fluctuation of allele frequencies, can lead to significant genetic changes, especially in small populations. Research on long-term avian studies has shown that genetic correlations can constrain the rate of adaptation, indicating that gene flow and genetic drift play complex roles in shaping evolutionary trajectories (Teplitsky et al., 2014). Furthermore, the study on the adaptation of songbirds to different altitudes underscores the importance of gene flow in maintaining genetic diversity and facilitating local adaptation (Yang et al., 2019). 2.4 Role of epigenetics in avian adaptation to environmental changes Epigenetic mechanisms, such as DNA methylation, histone modifications, and non-coding RNAs, play a crucial role in avian adaptation to environmental changes. These mechanisms can induce phenotypic changes without altering the underlying DNA sequence, allowing for rapid and reversible adaptation. For instance, a study on the epigenetic variation between two populations of Darwin’s finches, Geospiza fortis and G. fuliginosa (Figure 1), suggesting that DNA methylation contributes to local adaptation (Platt et al., 2015; McNew et al., 2017). Additionally, studies on invasive species have highlighted the importance of epigenetic variation in enabling rapid adaptation to new environments, with DNA methylation patterns being strongly influenced by local environmental conditions (Carneiro and Lyko, 2020; Chen et al., 2022). The concept of “bet hedging” against climate change further illustrates how epigenetic mechanisms can create multiple phenotypes from the same genotype, enhancing survival during extreme weather events (Burggren and Mendez-Sanchez, 2023).
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