Andreev Victor, Puzey Joshua, Davies Elizabeth, Olson-Manning Carrie, Kreutzmann Sydney, Fishbein Mark
Department of Plant Biology, Ecology, and Evolution, Oklahoma State University, Stillwater, Oklahoma, USA.
Biology Department, College of William and Mary, Williamsburg, Virginia, USA.
Mol Ecol. 2025 Sep;34(18):e70048. doi: 10.1111/mec.70048. Epub 2025 Aug 18.
Hybridisation affects the spatial and temporal patterns of morphological and genetic variation, shaping species evolution. Asclepias speciosa and A. syriaca provide an excellent system for uncovering how these patterns are generated. The ranges of A. speciosa and A. syriaca overlap on the North American Great Plains, and multiple intermediates are observed in this contact zone, consistent with hybridisation. However, other processes, such as preservation of ancestral polymorphism or selective pressure imposed by environmental clines, could explain the presence of morphological intermediates. In this study, we characterised patterns of variation within and between A. speciosa and A. syriaca using morphological and genetic data to validate the hybrid origin of intermediates, evaluate the impact of hybridisation on the parental species and reconstruct the demographic history of hybridisation events. In addition, we explored species-specific associations of genetic variation with climatic variables. We demonstrated that hybridisation best explains the occurrence of large numbers of morphologically intermediate individuals in the contact zone and documented bidirectional and asymmetric genetic introgression. We found a strong relationship between precipitation patterns and genetic variation in A. speciosa and A. syriaca, which suggests that the hybrid zone is maintained by differences in annual precipitation. We discovered that the timing of secondary contact is relatively recent, coinciding with rapid range shifts during the Pleistocene. Our findings provide new insights into the dynamics of hybridisation on the North American Great Plains, the setting for numerous contact zones between taxa affiliated with eastern and western biotas.
杂交会影响形态和遗传变异的空间和时间模式，从而塑造物种进化。美丽马利筋（Asclepias speciosa）和乳草（A. syriaca）为揭示这些模式是如何产生的提供了一个绝佳的系统。美丽马利筋和乳草在北美大平原的分布范围重叠，并且在这个接触区观察到多个中间类型，这与杂交现象相符。然而，其他过程，如祖先多态性的保留或环境渐变施加的选择压力，也可以解释形态中间类型的存在。在本研究中，我们利用形态学和遗传学数据来表征美丽马利筋和乳草内部及二者之间的变异模式，以验证中间类型的杂交起源，评估杂交对亲本物种的影响，并重建杂交事件的种群历史。此外，我们还探究了遗传变异与气候变量的物种特异性关联。我们证明，杂交最能解释接触区大量形态中间类型个体的出现，并记录了双向和不对称的基因渐渗。我们发现降水模式与美丽马利筋和乳草的遗传变异之间存在密切关系，这表明杂交区是由年降水量的差异维持的。我们发现二次接触的时间相对较近，与更新世期间快速的范围变化相吻合。我们的研究结果为北美大平原上杂交的动态过程提供了新的见解，北美大平原是东部和西部生物区系所属类群之间众多接触区的所在地。
