Center for Population Biology, One Shields Avenue, University of California, Davis, California 95616 USA.
Am J Bot. 2005 Nov;92(11):1827-35. doi: 10.3732/ajb.92.11.1827.
Polyploid speciation is an ongoing, important source of angiosperm diversity. However, the barriers to polyploid speciation and mechanisms of establishment remain poorly understood for all but a few species. Several factors likely to have influenced tetraploid establishment, including barriers to triploid formation, consequences of mixed-ploidy pollen loads, and the reproductive success of the minority cytotype, were examined in snow buttercups (Ranunculus adoneus) through a series of pollination and transplant experiments. Tetraploid snow buttercups do not have stigmatic barriers to pollen from diploid plants, nor does pollen from tetraploid plants have an advantage over pollen from diploids when on tetraploid stigmas. Tetraploid plants transplanted into a diploid population produced 50% fewer seeds than tetraploid plants in a tetraploid population. Intrinsic barriers to triploid formation were relatively weak, but few triploid seeds formed when mixed-ploidy pollen was present. Fecundity of triploid plants was very low, and no tetraploid offspring resulted. These results indicate that in snow buttercups, a triploid plant will contribute 0.8% of the tetraploid seeds of a minority tetraploid plant making it a minor contributor to the demographics of tetraploid establishment. The reproductive costs facing minority cytotype plants may explain the previously observed spatial segregation in snow buttercups.
多倍体形成是被子植物多样性的一个持续的重要来源。然而，除了少数几个物种外，对于所有物种来说，多倍体形成的障碍和建立的机制仍然知之甚少。通过一系列授粉和移植实验，研究了几种可能影响四倍体建立的因素，包括三倍体形成的障碍、混合倍性花粉负荷的后果，以及少数细胞型的生殖成功率，在雪毛茛（Ranunculus adoneus）中进行了研究。四倍体雪毛茛对来自二倍体植物的花粉没有柱头障碍，四倍体植物的花粉在四倍体柱头上也没有比二倍体花粉更具优势。移植到二倍体种群中的四倍体植物产生的种子比四倍体种群中的四倍体植物少 50%。三倍体形成的内在障碍相对较弱，但当存在混合倍性花粉时，形成的三倍体种子很少。三倍体植物的繁殖力非常低，没有产生四倍体后代。这些结果表明，在雪毛茛中，三倍体植物将贡献少数四倍体植物的 0.8%的四倍体种子，使其成为四倍体建立的种群动态的一个次要贡献者。少数细胞型植物面临的生殖成本可能解释了之前在雪毛茛中观察到的空间分离。
