Gross Karin, Schiestl Florian P
Institute of Systematic Botany, University of Zurich, Zollikerstrasse 107, CH-8008 Zurich, Switzerland.
Institute of Systematic Botany, University of Zurich, Zollikerstrasse 107, CH-8008 Zurich, Switzerland
Ann Bot. 2015 Feb;115(2):263-73. doi: 10.1093/aob/mcu244.
Polyploidization, the doubling of chromosome sets, is common in angiosperms and has a range of evolutionary consequences. Newly formed polyploid lineages are reproductively isolated from their diploid progenitors due to triploid sterility, but also prone to extinction because compatible mating partners are rare. Models have suggested that assortative mating and increased reproductive fitness play a key role in the successful establishment and persistence of polyploids. However, little is known about these factors in natural mixed-ploidy populations. This study investigated floral traits that can affect pollinator attraction and efficiency, as well as reproductive success in diploid and tetraploid Gymnadenia conopsea (Orchidaceae) plants in two natural, mixed-ploidy populations.
Ploidy levels were determined using flow cytometry, and flowering phenology and herbivory were also assessed. Reproductive success was determined by counting fruits and viable seeds of marked plants. Pollinator-mediated floral isolation was measured using experimental arrays, with pollen flow tracked by means of staining pollinia with histological dye.
Tetraploids had larger floral displays and different floral scent bouquets than diploids, but cytotypes differed only slightly in floral colour. Significant floral isolation was found between the two cytotypes. Flowering phenology of the two cytotypes greatly overlapped, and herbivory did not differ between cytotypes or was lower in tetraploids. In addition, tetraploids had higher reproductive success compared with diploids.
The results suggest that floral isolation and increased reproductive success of polyploids may help to explain their successful persistence in mixed-ploidy populations. These factors might even initiate transformation of populations from pure diploid to pure tetraploid.
多倍体化,即染色体组加倍,在被子植物中很常见,并具有一系列进化后果。新形成的多倍体系与它们的二倍体祖先在生殖上隔离,这是由于三倍体不育,但也容易灭绝,因为兼容的交配伙伴很少。模型表明,选型交配和生殖适合度的提高在多倍体的成功建立和持续存在中起着关键作用。然而,对于自然混合倍性种群中的这些因素知之甚少。本研究调查了两个自然混合倍性种群中影响传粉者吸引和效率以及二倍体和四倍体康诺顶冰花(兰科)植物繁殖成功的花部性状。
使用流式细胞术确定倍性水平,还评估了开花物候和食草情况。通过统计标记植物的果实和有活力的种子来确定繁殖成功率。使用实验阵列测量传粉者介导的花部隔离,通过用组织学染料对花粉块进行染色来追踪花粉流。
四倍体比二倍体有更大的花展示和不同的花香组合,但细胞型在花色上仅略有差异。在两种细胞型之间发现了显著的花部隔离。两种细胞型的开花物候有很大重叠,食草情况在细胞型之间没有差异或者在四倍体中较低。此外,与二倍体相比,四倍体有更高的繁殖成功率。
结果表明,多倍体的花部隔离和繁殖成功率的提高可能有助于解释它们在混合倍性种群中的成功持续存在。这些因素甚至可能引发种群从纯二倍体向纯四倍体的转变。