Parapatric evolution at the population-species interface and the adaptive significance of genetic clines

在一个连续的景观中，沿环境梯度的主要生态适应性假设了parparatric多样化。这个过程产生了遗传变异，其中每个变异的宽度是由选择和基因流动之间的平衡决定的。面对同质化的基因流，导致物种形成的异种多样化是有争议的，但必须包括二次选择，包括积极的分类交配。因此，主要选择和次要选择之间的相互作用应该决定特定分化的命运。本研究将野外资料、实验室实验和遗传分析相结合，综合研究了两个相邻种群之间的遗传变异及其适应意义。本研究探讨了这两个种群在种群和物种之间的连续体中的位置，并分析了基因流在准种群多样化过程中的主要选择和次要选择的相对重要性。该研究引入了基因分型测序来测试整个基因组的遗传差异，量化异常位点的分布。异常位点通常被解释为受分化选择和/或导致生殖隔离的影响，但这很少被直接测试，这是本研究的主要目的。

Parapatric diversification assumes primary, ecological adaptation along an environmental gradient in a continuous landscape. The process results in genetic clines where the width of each cline is determined by a balance between selection and gene flow. In the face of homogenising gene flow, parapatric diversification leading to speciation is controversial but must include secondary selection involving positive assortative mating. The interaction between primary and secondary selection should therefore determine the fate of specific divergence. The present study combines field data, laboratory experiments and genetic analyses in an integrative approach to study the evolution and adaptive significance of genetic clines between two contiguous populations of the tephritid fly Urophora cardui. The study addresses where the two populations are found in the continuum between population and species, and it analyses the relative importance of primary and secondary selection with gene flow in the parapatric diversification process. The study introduces genotyping-by-sequencing to test genetic divergence across the genome, quantifying the distribution of outlier loci. Outlier loci are generally interpreted as being affected by divergent selection and/or causing reproductive isolation but this has rarely been directly tested, which is a major aim of the present study.