International Journal of Molecular Evolution and Biodiversity 2024, Vol.14, No.2, 80-90 http://ecoevopublisher.com/index.php/ijmeb 83 Lai et al. (2019) found that the genetic differentiation between high- and low-altitude populations of the vinous-throated parrotbill in central Taiwan is significant. By analyzing the distribution of F_ST and ΔF_ST across the genome, they identified several candidate regions that might be associated with local adaptation to different altitudes. These regions, marked as red dots, represent the top 1% of F_ST and ΔF_ST values, indicating high genetic differentiation. The study suggests that the parrotbill populations on either side of the Central Mountain Range (CMR) exhibit distinct genetic structures, influenced by the altitudinal variation. This differentiation likely reflects adaptive responses to the diverse environmental conditions across the altitudinal gradient, contributing to our understanding of how geographic and ecological factors drive genetic divergence in avian species. 3.2 Genetic drift Genetic drift, the random fluctuation of allele frequencies, has a pronounced impact on small populations. It can lead to significant genetic changes over time, independent of selective pressures. In small populations, genetic drift can reduce genetic diversity and potentially limit adaptive potential. For example, studies on adaptive divergence in fission yeast populations under varying degrees of gene flow revealed that genetic drift, along with demography, can constrain the speed of adaptation (Stephan, 2021). Furthermore, research on Arabidopsis lyrata populations showed that genetic drift, combined with local selection and gene flow, influences the genomic patterns of local adaptation8. These case studies highlight the complex interplay between genetic drift and other evolutionary forces in shaping adaptation (Bonnet et al., 2022). 3.3 Gene flow and migration Gene flow, the movement of genes between populations, introduces new genetic material and can either facilitate or hinder adaptation. It can increase genetic diversity and provide raw material for selection, but excessive gene flow can also swamp local adaptation by homogenizing populations. Experimental evolution studies on fission yeast demonstrated that adaptive divergence was most pronounced in the absence or presence of maximal gene flow, while intermediate levels of migration reduced divergence (Tusso et al., 2021). Similarly, research on Arabidopsis lyrata indicated that gene flow from high to low altitudes played a significant role in local adaptation, with asymmetric migration patterns affecting the genetic architecture of adaptive traits. These findings illustrate the dual role of gene flow in promoting and constraining adaptation. 3.4 Mutation Mutations are the ultimate source of genetic variation, providing new alleles that can be acted upon by natural selection. They are essential for generating the genetic diversity necessary for adaptive evolution. For instance, studies on Drosophila simulans exposed to a new temperature regime revealed a polygenic architecture of adaptive traits, with high genetic redundancy among beneficial alleles (Barghi et al., 2019). This research showed that natural populations harbor a vast reservoir of adaptive variation, facilitating rapid evolutionary responses through multiple genetic pathways. Additionally, research on high-altitude adaptation in various species has highlighted the role of novel mutations in driving phenotypic and genetic changes under strong selective pressures. These examples underscore the importance of mutations in generating the genetic diversity required for adaptation. 3.5 Sexual Selection Sexual selection, a form of natural selection, influences the development of traits that enhance mating success and can lead to increased species diversity. It operates through mate choice and competition for mates, driving the evolution of traits that may not necessarily improve survival but increase reproductive success. For example, research on threespine stickleback demonstrated that predator presence altered selection on defensive armor traits and underlying genes, highlighting the role of biotic interactions in driving sexual selection and species divergence (Hämälä and Savolainen, 2019). Additionally, studies on the adaptive potential of wild animal populations have shown that sexual selection can interact with other selective pressures, influencing the evolution of multiple traits (Hao and Lei, 2022). These findings illustrate the significant impact of sexual selection on trait development and species diversity. In summary, the mechanisms of natural selection, genetic drift, gene flow,
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