![]() For example, local genetic drift in combination with spatially restricted gene flow (i.e. ![]() genetic drift and gene flow) may also generate correlations between phenotype frequencies and environmental gradients. While clines are often interpreted as strong evidence of adaptive evolution, non-adaptive processes (e.g. The multiple evolutionary mechanisms structuring clines have prompted their continued use by evolutionary biologists seeking to explore the relative contributions of non-adaptive and adaptive evolutionary processes in structuring patterns of genetic and phenotypic diversity and differentiation within and between populations. Clines arise and are maintained via the interplay of genetic drift, gene flow and natural selection across an environmental gradient. Studies of heritable phenotypic change in urban populations should generate null models of phenotypic evolution based on the genetic architecture underlying focal traits prior to invoking selection's role in generating adaptive differentiation.Įvolutionary clines-changes in the frequency of a genotype or a heritable phenotype over a geographical area -have long served as model systems in evolutionary biology. Gradients in the strength of drift across a landscape resulted in phenotypic clines with lower frequencies of HCN in strongly drifting populations, giving the misleading appearance of deterministic adaptive changes in the phenotype. Our results demonstrate that the genetic architecture of this trait makes natural populations susceptible to decreases in HCN frequencies via drift. ![]() HCN results from an epistatic interaction between two Mendelian-inherited loci. In this paper, we use spatially explicit simulations modelled according to the cyanogenesis (hydrogen cyanide, HCN) polymorphism in white clover ( Trifolium repens) to examine the formation of phenotypic clines along urbanization gradients under varying levels of drift, gene flow and selection. While the presence of parallel clines in heritable phenotypic traits is often considered strong evidence for the role of natural selection, non-adaptive evolutionary processes can also generate clines, and this may be more likely when traits have a non-additive genetic basis due to epistasis. Urban environments offer the opportunity to study the role of adaptive and non-adaptive evolutionary processes on an unprecedented scale.
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