Department of Genetics, University of Georgia, Athens, Georgia, 30602.
Department of Biology, University of Richmond, Richmond, Virginia, 23173.
Evolution. 2021 Mar;75(3):600-613. doi: 10.1111/evo.14105. Epub 2020 Oct 26.
Species are often defined by their ability to interbreed (i.e., Biological Species Concept), but determining how and why reproductive isolation arises between new species can be challenging. In the Mimulus tilingii species complex, three species (M. caespitosa, M. minor, and M. tilingii) are largely allopatric and grow exclusively at high elevations (>2000 m). The extent to which geographic separation has shaped patterns of divergence among the species is not well understood. In this study, we determined that the three species are morphologically and genetically distinct, yet recently diverged. Additionally, we performed reciprocal crosses within and between the species and identified several strong postzygotic reproductive barriers, including hybrid seed inviability, F1 hybrid necrosis, and F1 hybrid male and female sterility. In this study, such postzygotic barriers are so strong that a cross between any species pair in the M. tilingii complex would cause nearly complete reproductive isolation. We consider how geographical and topographical patterns may have facilitated the evolution of several postzygotic barriers and contributed to speciation of closely related members within the M. tilingii species complex.
物种通常通过其能够杂交的能力来定义（即生物物种概念），但确定新物种之间生殖隔离是如何以及为何产生的可能具有挑战性。在拟南芥属 tilingii 种复合体中，三个物种（M. caespitosa、M. minor 和 M. tilingii）在很大程度上是异域分布的，并且仅在高海拔地区（>2000 米）生长。地理隔离在多大程度上塑造了物种之间的分化模式还不太清楚。在这项研究中，我们确定这三个物种在形态和遗传上是不同的，但最近才分化出来。此外，我们在物种内和物种间进行了相互杂交，并鉴定出几种强烈的合子后生殖障碍，包括杂种种子不育、F1 杂种坏死和 F1 杂种雄性和雌性不育。在这项研究中，这种合子后障碍非常强烈，以至于拟南芥属 tilingii 复合体中的任何物种对之间的杂交都会导致几乎完全的生殖隔离。我们考虑地理和地形模式如何促进了几种合子后障碍的进化，并促成了拟南芥属 tilingii 种复合体中密切相关成员的物种形成。
