长柱剪秋罗和剪秋罗属间不对称的同种花粉优势。
Asymmetrical conspecific seed-siring advantage between Silene latifolia and S. dioica.
机构信息
Department of Biology, Indiana University, Bloomington, IN 47405, USA.
出版信息
Ann Bot. 2010 Apr;105(4):595-605. doi: 10.1093/aob/mcq013. Epub 2010 Feb 10.
BACKGROUND AND AIMS
Silene dioica and S. latifolia experience only limited introgression despite overlapping flowering phenologies, geographical distributions, and some pollinator sharing. Conspecific pollen precedence and other reproductive barriers operating between pollination and seed germination may limit hybridization. This study investigates whether barriers at this stage contribute to reproductive isolation between these species and, if so, which mechanisms are responsible.
METHODS
Pollen-tube lengths for pollen of both species in styles of both species were compared. Additionally, both species were pollinated with majority S. latifolia and majority S. dioica pollen mixes; then seed set, seed germination rates and hybridity of the resulting seedlings were determined using species-specific molecular markers.
KEY RESULTS
The longest pollen tubes were significantly longer for conspecific than heterospecific pollen in both species, indicating conspecific pollen precedence. Seed set but not seed germination was lower for flowers pollinated with pure heterospecific versus pure conspecific pollen. Mixed-species pollinations resulted in disproportionately high representation of nonhybrid offspring for pollinations of S. latifolia but not S. dioica flowers.
CONCLUSIONS
The finding of conspecific pollen precedence for pollen-tube growth but not seed siring in S. dioica flowers may be explained by variation in pollen-tube growth rates, either at different locations in the style or between leading and trailing pollen tubes. Additionally, this study finds a barrier to hybridization operating between pollination and seed germination against S. dioica but not S. latifolia pollen. The results are consistent with the underlying cause of this barrier being attrition of S. dioica pollen tubes or reduced success of heterospecifically fertilized ovules, rather than time-variant mechanisms. Post-pollination, pre-germination barriers to hybridization thus play a partial role in limiting introgression between these species.
背景与目的
尽管石竹属的二型腺萼组石竹（Silene dioica）和宽叶组石竹（S. latifolia）的开花物候、地理分布和一些传粉者共享存在重叠，但它们只经历了有限的基因渗入。同种花粉优先和在传粉和种子萌发之间起作用的其他生殖障碍可能限制杂交。本研究调查了这一阶段的障碍是否有助于这两个物种之间的生殖隔离，如果是这样，哪些机制是负责的。
方法
比较了这两个物种的花粉在这两个物种的花柱中的花粉管长度。此外，用大多数石竹属宽叶组和大多数二型腺萼组石竹的花粉混合物对这两个物种进行了授粉；然后，使用种特异性分子标记来确定授粉后种子的结实率、种子萌发率和杂种幼苗的杂种性。
主要结果
在这两个物种中，同种花粉的花粉管比异种花粉的花粉管长得明显更长，表明同种花粉优先。与纯同种花粉相比，用纯异种花粉授粉的花朵的结实率较低，但种子萌发率没有降低。在石竹属的花授粉中，混合物种授粉导致非杂种后代的比例过高，但在二型腺萼组石竹的花授粉中则没有。
结论
在石竹属花中发现的花粉管生长的同种花粉优先，但种子产生的父本不是这种情况，这可能是由于花粉管生长速率的变化造成的，这种变化可能发生在花柱的不同位置，也可能发生在领先花粉管和尾随花粉管之间。此外，本研究发现，在授粉和种子萌发之间存在一个杂交障碍，该障碍针对二型腺萼组石竹的花粉，但不针对宽叶组石竹的花粉。研究结果表明，造成这种障碍的原因可能是二型腺萼组石竹花粉管的损耗或异种受精的胚珠成功率降低，而不是时间变化的机制。因此，授粉后、萌发前的杂交障碍在限制这两个物种的基因渗入方面发挥了部分作用。
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