Data from: Transmission advantage favors selfing allele in experimental populations of self-incompatible Witheringia solanacea (Solanaceae)

The evolution of self-fertilization is one of the most commonly traversed transitions in flowering plants, with profound implications for population genetic structure and evolutionary potential. We investigated factors influencing this transition using Witheringia solanacea, a predominantly self-incompatible (SI) species within which self-compatible (SC) genotypes have been identified. We showed that self-compatibility in this species segregates with variation at the S-locus as inherited by plants in F1 and F2 generations. To examine reproductive assurance and the transmission advantage of selfing, we placed SC and SI genotypes in genetically replicated gardens and monitored male and female reproductive success, as well as selfing rates of SC plants. Self-compatibility did not lead to increased fruit or seed set, even under conditions of pollinator scarcity, and the realized selfing rate of SC plants was less than 10%. SC plants had higher fruit abortion rates, consistent with previous evidence showing strong inbreeding depression at the embryonic stage. Although the selfing allele did not provide reproductive assurance under observed conditions, it also did not cause pollen discounting, so the transmission advantage of selfing should promote its spread. Given observed numbers of S-alleles and selfing rates, self-compatibility should spread even under conditions of exceedingly high initial inbreeding depression.

自花授粉（self-fertilization）的演化是被子植物中最常发生的演化过渡事件之一，对种群遗传结构与演化潜力具有深远影响。本研究以睡茄属物种Witheringia solanacea为研究对象，探究驱动这一过渡过程的影响因素；该物种以自交不亲和（self-incompatible, SI）为主，目前已在其中鉴定出自交亲和（self-compatible, SC）基因型。我们证实，该物种的自交亲和性与S基因座（S-locus）的变异连锁，并在子一代（F1）和子二代（F2）植株中呈现遗传分离。为探究自交的生殖保障（reproductive assurance）与传播优势（transmission advantage），我们将SC与SI基因型植株种植于遗传重复的实验花园中，监测其雌雄生殖适合度，同时记录SC植株的自交率。研究结果显示，即便在传粉者匮乏的条件下，自交亲和性也未提升坐果率或结籽量；且SC植株的实际自交率不足10%。此外，SC植株的果实败育率更高，这与此前报道的胚胎阶段存在强烈近交衰退（inbreeding depression）的证据相符。尽管在本研究观测的条件下，自交等位基因未带来生殖保障，但它也未引发花粉贴现（pollen discounting），因此自交的传播优势应能推动该等位基因的扩散。结合观测到的S等位基因数量与自交率，即便在初始近交衰退程度极高的条件下，自交亲和性也应能够得以扩散。