Shifts to earlier selfing in sympatry may reduce costs of pollinator sharing

Coexisting plant congeners often experience strong competition for resources. Competition for pollinators can result in direct fitness costs via reduced seed set or indirect costs via heterospecific pollen transfer (HPT), causing subsequent gamete loss and unfit hybrid offspring production. Autonomous selfing may alleviate these costs, but to preempt HPT, selfing should occur early, before opportunities for HPT occur (i.e. “preemptive selfing hypothesis”). We evaluated conditions for this hypothesis in Collinsia sister species, C. linearis and C. rattanii. In field studies, we found virtually identical flowering times and pollinator sharing between congeners in sympatric populations. Compared to allopatric populations, sympatric C. linearis populations enjoyed higher pollinator visitation rates, whereas visitation to C. rattanii did not differ in sympatry. Importantly, the risk of HPT to each species in sympatry was strongly asymmetrical; interspecies visits comprised 40% of all flower-...同域共存的同属植物（congener）通常会面临激烈的资源竞争。传粉者竞争可通过降低结籽率带来直接的适合度代价，或通过异种花粉传递（heterospecific pollen transfer, HPT）引发间接代价，进而导致配子损耗以及低活力杂交后代的产生。自动自交（autonomous selfing）或可缓解此类代价，但为了抢先阻断异种花粉传递，自交需在异种花粉传递机会出现前提前发生（即"先发制人自交假说"）。我们在柯林草属（Collinsia）的两个姊妹物种——线形叶柯林草（C. linearis）与拉坦氏柯林草（C. rattanii）中，对该假说的适用条件开展了评估。野外研究结果显示，同域种群内的两个同属植物类群，其开花时间几乎完全一致，且共享相同的传粉者。与异域种群相比，同域分布的线形叶柯林草种群拥有更高的传粉者访问频率，而同域分布的拉坦氏柯林草的传粉者访问频率则无显著差异。尤为关键的是，同域种群中两个物种面临的异种花粉传递风险存在显著不对称性；跨物种访花占总访花事件的40%，且……