Department of Biology, East Carolina University, Mailstop 551, Greenville, NC 27858, USA.
Am J Bot. 2013 Jun;100(6):1002-13. doi: 10.3732/ajb.1200616. Epub 2013 Mar 17.
The roles of hybridization and mating systems in the evolution of angiosperms have been well studied, but less work has focused on their interactions. Self-incompatible and self-compatible species often show asymmetry in heterospecific pollen rejection. Self-fertilization can preempt ovules before opportunities for hybridization. In turn, hybridization might affect mating system evolution through selection for selfing to avoid production of low fitness hybrids. •
AFLP and morphological analyses were used to test for hybrids in a contact zone between species with contrasting breeding systems. Crossing experiments examined the relative contributions to reproductive isolation of pollen-pistil interactions, timing of self-fertilization, and F1 viability and fertility. A diallel cross of siblings tested for an association between heterospecific incompatibility and S-genotype in the self-incompatible species. •
A low frequency of hybrids was detected in the contact zone. Pollen-pistil interactions were partially consistent with the SI × SC rule; some individuals of the self-incompatible species rejected heterospecific pollen, whereas the self-compatible species was fully receptive to it. In the selfing species, individuals with early selfing produced fewer hybrid progeny than did those with delayed self-compatibility when heterospecific pollen was applied after self-pollen. Viability of F1s was high but fertility was low. Variability in heterospecific pollen rejection was not related to S-genotype. •
Both self-fertilization and self-incompatibility are associated with limits to hybridization at this site. The strong effect of timing of selfing on production of low fitness F1s suggests that hybridization might select for early selfing in this population.
杂交和交配系统在被子植物进化中的作用已经得到了很好的研究，但很少有工作关注它们的相互作用。自交不亲和和自交亲和物种在异交花粉排斥方面通常表现出不对称性。自交可以在杂交机会之前预先消耗胚珠。反过来，杂交可能会通过选择自交来避免产生低适合度的杂种而影响交配系统的进化。
使用 AFLP 和形态分析来检测具有不同繁殖系统的物种接触区中的杂种。杂交实验研究了花粉-柱头相互作用、自交时间以及 F1 活力和生育力对生殖隔离的相对贡献。对同胞进行的双列杂交检验了自交不亲和物种中异交不相容性和 S 基因型之间的关联。
在接触区检测到低频率的杂种。花粉-柱头相互作用部分符合 SI × SC 规则；自交不亲和物种的一些个体排斥异交花粉，而自交亲和物种则完全接受它。在自交物种中，当异交花粉在自交花粉后应用时，早自交的个体比延迟自交的个体产生的杂种后代更少。F1 的活力很高，但生育力很低。异交花粉排斥的变异性与 S 基因型无关。
在这个地点，自交和自交不亲和都与杂交的限制有关。自交时间对产生低适合度 F1 的强烈影响表明，在该种群中，杂交可能选择了早期自交。
