International Journal of Molecular Ecology and Conservation, 2025, Vol.15, No.2, 74-82 http://ecoevopublisher.com/index.php/ijmec 78 4.2 Historical dispersal and phylogeographic patterns of domestic duck breeds across climate regions Genomic analysis indicates that Asian domestic duck populations are geographically divided into Southeast/South Asian, wild, and local Chinese. Historical demographic reconstructions indicate that Southeast/South Asian and Chinese domestic ducks experienced strong population bottlenecks, particularly during domestication and the last glacial maximum. Despite such bottlenecks, there has been widespread and enduring gene flow among neighboring populations, especially between Guangxi (China) and Southeast/South Asia, that has shaped the current genetic structure of domestic ducks in climatic regions (Jiang et al., 2021). Phylogeographic studies of wild ducks, such as the Harlequin Duck, also show that early colonization from glacial refugia and contact events subsequently have encouraged regional and continental-scale genetic differentiation (Scribner et al., 2024). 4.3 Influence of hydrology and habitat changes on dispersal and isolation Hydrological regimes and habitat dynamics are the principal reasons for duck dispersal and population fragmentation. Seasonal and inter-annual timescale changes in water level, food and habitat structure affect ducks' abundance and mobility. For example, the body shape and mass of Chinese coastal wetland ducks are based on the coverage and connectivity of wetland habitats and tidal flats that also determine their seed dispersal role (Luo et al., 2024). In the Baltic Sea, water quality and water nutrient levels regulated through processes such as runoff fertilizer have direct effects on long-tailed duck population and overwintering success (Rintala et al., 2022). 4.4 Dual Impacts of anthropogenic interference and natural barriers on population structure The organization of duck populations is shaped by human-induced and natural influences (e.g., climate change, land cover change, hunting) and natural barriers (e.g., ocean basins, geographic distance). Historical records throughout North America suggest that the ranges of ducks have adapted to changing climate and land cover and show species- and subpopulation-specific autumn and winter northward or southward migration (Verheijen et al., 2023; 2024). Within the subarctic and Arctic, climate change and human activity threaten significant habitats, encouraging elevation in isolation and modifying migration corridors (Karwinkel et al., 2020). Genetic analysis confirms vicariance during the past and recent gene flow are accountable for spatial patterns of duck genes as natural and human-made structures jointly condition differentiation and connectivity (Jiang et al., 2021; Scribner et al., 2024). 5 Adaptive Evolutionary Mechanisms of Ducks in Different Ecological Zones 5.1 Morphological and physiological adaptations under habitat variation Ducks illustrate typical skeleton and physiological specializations to ecological niches. Mallards possess dense and heavy bones adapted for generalized locomotion and utilization of diversified environments, while Green-Winged Teals possess less dense and lighter bones adapted to enable speed in flight in shallow wetland environments. Tufted Ducks, being deep-divers, illustrate heavy and rigid bones adapted to underwater searching (Osiak-Wicha et al., 2024). Duck species that inhabit high altitudes possess physiological specializations towards hypoxia, including structure and function adaptations of hemoglobin to enable the transport of oxygen in hypoxic environments (Graham and McCracken, 2019). 5.2 Genomic-level adaptive differences and functional gene analysis Genomic research establishes adaptive evolution in ducks to involve regulatory and structural genetic innovations. Convergent evolution of high-altitude ducks is observed in hypoxia-inducible factor (HIF) pathway gene EGLN1 and EPAS1, consistent with vertebrate high-altitude adaptation (Graham and McCracken, 2019). Positive selection in tissue repair, immune response, and anti-tumorous activity is observed in the Chinese crested duck, reflecting life's gene compensation and gene stability preservation mechanisms. TAS2R40 harbors a causative crest character mutation in this breed (Chang et al., 2023). 5.3 Evolutionary trends in ecological niche differentiation and behavioral adaptation Phenotypic and behavioral divergence to ecological niche filling causes adaptive radiation in dabbling ducks. Variation in bill shape creates variation in foraging efficiency and prey preference that results in niche partitioning of sympatric species. Aggression and mate preference are other behavioral characters that are involved in ecological speciation and maintenance of species boundaries. Ecological pressures and sexual selection contribute to cause reproductive isolation and phenotypic divergence (Brown et al., 2022).
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