Barriers to gene flow between divergent populations result in contact (hybrid) zones. Locations where multiple contact zones overlap can be used in comparative studies asking: what mechanisms maintain barriers; what is the origin of the genetic variation involved; and do differences in life history affect the nature of barriers? In a review of 23 marine species’ genetic divergence over a postglacial salinity gradient, many showed steep genetic clines supported by divergent selection and/or temporal or spatial segregation. Contacts were primary or secondary and shaped by ancestral variation sometimes involving inversions. The dispersal potential of species seemed less important in shaping clines. Studies of multispecies contact zones will increase our understanding of speciation, but we need to address the taxonomic bias and focus more on postzygotic isolation.

基因在不同群体之间流动的障碍导致了接触（杂交）区。可以在比较研究中使用多个接触区域重叠的位置，这些问题询问：什么机制可以维持障碍？涉及的遗传变异的起源是什么？生活史的差异会影响障碍的性质吗？在对冰期后盐度梯度上23种海洋物种的遗传差异的综述中，许多研究表明，陡峭的遗传系受到发散选择和/或时间或空间隔离的支持。接触是主要的或次要的，并且由祖先的变异形成，有时涉及倒置。物种的扩散潜力在塑造氏族中似乎不太重要。对多物种接触区的研究将增进我们对物种形成的理解，