Data from: The relationship between post-mating reproductive isolation and reinforcement in Phlox

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 post-mating 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（speciation）过程涉及分化谱系间生殖隔离（reproductive isolation, RI）的累积。自然选择可通过强化作用（reinforcement）途径促进生殖隔离的增强：此时杂交带来的适应性代价，会对提升合子前生殖隔离的性状产生选择压力。强化作用可导致至少一个类群出现表型分化，该分化源于同域类群间代价高昂的杂交。驱动强化作用的选择强度，由杂交代价与杂交频率共同决定。
我们以目前研究最为深入的生殖强化案例类群——福禄考属（Phlox）物种为研究对象，通过量化其物种间的交配后生殖隔离屏障，探究杂交代价对生殖强化的影响。我们明确了经历过与未经历过生殖强化的谱系间，生殖隔离强度是否存在差异；测定了物种内生殖隔离的变异程度；并检验了生殖隔离是否与系统发育亲缘关系相关联。
研究发现，因生殖强化出现表型分化的物种间生殖隔离水平较高，但其余物种类群间的生殖隔离程度同样显著。我们还观察到物种内个体间的生殖隔离存在广泛变异，且未发现生殖隔离强度与系统发育亲缘关系存在关联的证据。
本研究认为，在该演化支（clade）中，由生殖强化导致的表型分化与杂交及基因渐渗（introgression）的频率相关，而非与杂交代价相关。