Suni Sevan S, Hopkins Robin
The Arnold Arboretum of Harvard University, 1300 Centre Street, Boston, MA 02131.
Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA.
Evolution. 2018 May 18. doi: 10.1111/evo.13507.
The process of speciation involves the accumulation of reproductive isolation (RI) between diverging lineages. Selection can favor increased RI via the process of reinforcement, whereby costs to hybridization impose selection for increased prezygotic RI. Reinforcement results in phenotypic divergence within at least one taxon, as a result of costly hybridization between sympatric taxa. The strength of selection driving reinforcement is determined by the cost of hybridization and the frequency of hybridization. We investigated the cost of hybridization by quantifying postmating RI barriers among Phlox species that comprise one of the best-studied cases of reinforcement. We determined if the strength of RI differs among lineages that have and have not undergone reinforcement, how much variability there is within species in RI, and whether RI is associated with phylogenetic relatedness. We found high RI for the species that underwent phenotypic divergence due to reinforcement; however, RI was also high between other species pairs. We found extensive variability in RI among individuals within species, and no evidence that the strength of RI was associated with phylogenetic relatedness. We suggest that phenotypic divergence due to reinforcement is associated with the frequency of hybridization and introgression, and not the cost of hybridization in this clade.
物种形成过程涉及到分化谱系之间生殖隔离（RI）的积累。选择可以通过强化过程促进RI的增加，即杂交成本促使对增加合子前RI进行选择。由于同域分类群之间代价高昂的杂交，强化导致至少一个分类群内出现表型分化。驱动强化的选择强度由杂交成本和杂交频率决定。我们通过量化福禄考属植物物种之间的交配后RI障碍来研究杂交成本，福禄考属植物是强化研究最充分的案例之一。我们确定了经历过强化和未经历过强化的谱系之间RI强度是否不同、物种内部RI存在多大变异性以及RI是否与系统发育相关性有关。我们发现，因强化而发生表型分化的物种具有较高的RI；然而，其他物种对之间的RI也很高。我们发现物种内个体间的RI存在广泛变异性，并且没有证据表明RI强度与系统发育相关性有关。我们认为，在这个进化枝中，因强化而导致的表型分化与杂交和基因渗入的频率有关，而不是与杂交成本有关。
