[POS] Evolution and Genetics

[POS-46] Phenotypic Clines Shaped by Gene Flow and Selection Gradients

*Yoshinori Miyake¹, Yuya Fukano², Koichiro Tamura¹, Yuuya Tachiki¹ (1. Tokyo Metropolitan University (Japan), 2. Chiba University (Japan))

Keywords:

Urban evolution,Metapopulation,Adaptive evolution

Urbanization significantly alters ecosystems by imposing novel selective pressures, such as elevated temperatures, pollution, and changing interspecific interactions, which drives evolutionary changes in urban organisms. In addition, habitat fragmentation associated with urbanization reduces gene flow and amplifies genetic drift, potentially constraining adaptive evolution. The interaction among these evolutionary processes along the urban-rural gradient gives rise to geographic patterns in phenotypes, providing insights into both adaptive and non-adaptive evolution. A well-studied example of a phenotypic cline in urban evolution is the hydrogen cyanide (HCN) polymorphism of white clover (Trifolium repens), which is a defensive trait against herbivory. Urban habitats typically less suffer from herbivorous pressure, which is associated with decreased HCN frequency. However, global-scale analyses have revealed deviations from the expected urban-rural pattern, suggesting that a range of factors, including local environmental variability and stochasticity, should influence shaping the patterns. Here, we developed a metapopulation model based on the Wright-Fisher framework to capture the stochastic processes driving urban evolution. The model incorporated geographic gradients in both selection and migration rate among subpopulations. We explain how adaptive clines emerged under restricted gene flow. Especially, when gene flow was severely restricted in urban area, phenotypic cline was reversed adaptive clines. The resulting cline well fitted with an empirical observation, including cases that deviate from the expected urban–rural gradient, and potentially explained the mechanisms in terms of stochastic processes.