Rausher Mark D, Augustine David, VanderKooi Amy
Department of Zoology, Box 90325, Duke University, Durham, North Carolina, 27708-0325.
Evolution. 1993 Dec;47(6):1688-1695. doi: 10.1111/j.1558-5646.1993.tb01261.x.
Throughout southeastern North America, the annual morning glory Ipomoea purpurea exhibits a polymorphism at a locus that influences the intensity of floral pigmentation. Previous studies have shown that when rare, the homozygous white genotype has a greater selfing rate than the homozygous dark genotype. In the absence of pollen discounting (a reduction in transmission of pollen to other plants by genotypes that exhibit increased selfing) and inbreeding depression, this increased selfing rate should favor the white allele. Experiments reported here confirm that the white genotype has elevated selfing rates when rare but indicate pollen discounting is not associated with elevated selfing. Rather, white genotypes contribute more pollen to the outcross pollen pool. The disparity between genotypes in both selfing rates and success at pollen contribution to other plants disappears at intermediate to high frequencies of the white allele. Pollinator movements are consistent with the pattern of selfing. These results suggest that elevated selfing and enhanced success at pollen donation contribute to maintenance of the white allele in natural populations of morning glories.
在北美东南部，一年生的紫牵牛（Ipomoea purpurea）在一个影响花色素沉着强度的基因座上表现出多态性。先前的研究表明，当白色纯合基因型罕见时，其自交率比深色纯合基因型更高。在不存在花粉折扣（即表现出自交增加的基因型向其他植物传递花粉的能力降低）和近亲繁殖衰退的情况下，这种增加的自交率应该有利于白色等位基因。本文报道的实验证实，白色基因型在罕见时自交率会升高，但表明花粉折扣与自交率升高无关。相反，白色基因型会向异交花粉库贡献更多花粉。在白色等位基因处于中等至高频率时，基因型在自交率和对其他植物花粉贡献的成功率方面的差异消失。传粉者的活动与自交模式一致。这些结果表明，自交增加和花粉捐赠成功率提高有助于紫牵牛自然种群中白色等位基因的维持。
